µCL stand for MicroController Language. It has the following basic goals:
This language specification tends to follow the same overall structure as other language specications; namely it discusses lexical issues first, followed by global declarations, procedure declarations, statements, and expressions.
The term "lexical" is a computer science term that roughly corresponds to the character, word, and punctuation rules for a program.
Early programs were done on punched cards using the Hollerith character codes. The unlamented punched cards were eventually replaced with 7-bit ASCII (American Standard Code for Information Interchange.) µCL programs uses an 8-bit character code called Latin-9 which has 7-bit ASCII embedded in its first half and some additional character codes suitible for European languages in its second half. The official name for Latin-9 is ISO-8859-15, where ISO stands for International Standards Organization, 8859 is the number reserved for 8-bit character code standards, and 15 is the standard number used for Latin-9. What this means to the average µCL user is that symbols and strings can contain characters with accents, tildes, and umlauts and there are some additional non-letter symbols such as the Euro currency symbol ('= code 164 decimal) are available for inclusion in string and character constants.
A µCL program is broken into a sequence of lines, where each line is terminated by the LF character (Line-Feed = code 10 decimal.) There are many computer systems that insert an extra CR character (Carriage-Return = code 13 decimal) before each LF character. In µCL, the CR character before each LF character is silently ignored. The CR and CR-LF sequence is called the end of line. The average µCL user does not need to worry about any of this, whenever you need to start a new line, just press the [Enter] key, and the a new line will be started; the underlying editor will deal with the CR and LF stuff appropriately.
In general, each µCL declaration and statement occupies one line. Line comments start with a hash character ('#' = code 35 decimal) and continue to the end of line. A fragment of a µCL program is shown below:
ucl 1.0 # Line 1
# Line 2 (blank)
# Copyright © 2004 by Gramlich # Line 3 (comment)
# Line 4 (blank)
library PIC16F876A # Line 5
Note that this µCL program fragment has the Latin-9 character for copyright ('©' = code 169 decimal.) on the third line.
In addition to treating end of line as a statement and declaration termination, µCL uses indentation to specify nested statements and declarations. The Python programming language has popularized this concept. Some example code with indentation is shown below:
# All procedure declarations start at indentation
# level 0 (i.e. no preceeding white space.)
procedure maximum
# Indentation level 1. All procedure arguments
# and statements start at this level.
argument a byte
argument b byte
returns byte
if a > b
# Indentation level 2. All "then" clause
# statements occur at one indentation level
# greater than parent "if" statement.
return a
# The end of "then" clause reverts to
# previous indentation level.
# Back to indentation level 1.
return b
# End of arguments and statements reverts to
# previous indentation level:
# Back to indentation level 0.
# More declarations follow here with no indenation.
global variable x
global variable y
This example shows an µCL procedure for computing the maximum of two
values. The initial declaration line is not indented at all and
specifies the procedure name -- maximum. All subsequent
procedure declarations (e.g. argument and returns
) and procedure statements (e.g. if and return
) must be indented by at least one level. The if statement
starts at indentation level 1 and has its "then" clause at indentation
level 2. At the end of the "then" clause, indentation returns level 1.
Similarly, the end of the procedure is indicated by a return to
indentation level 0.
The details for figuring out indentation are based on the column number for the first printing character (i.e. not a space or tab) on a line. If a line contains no printing characters, it is treated as a blank line and is ignored by the µCL language for indentation level determination. All lines in a sequence that are at the same column number (ignoring blank lines) are considered to be at the same indentation level.
Determining the column number of a line is complicated by the TAB character (= code 8 decimal.) For µCL, tab stops occur every 8 spaces. The occurrance of a tab advances the column number to the next multiple of 8 plus 1. The beginning of the line is at column 1. A tab at the beginning of a line advances to column 9 (= 8 + 1.) Another tab advances to column 17 (= 2×8 + 1.) A tab at column 13 also advances to column 17. For the average µCL user, if the code looks properly indented on the screen, the compiler will "see" the same indentation and behave accordingly.
Each time the column number for a line is greater than the previous printing line, the indentation level is incremented by one. When the column number for a line is less than the previous printing line, the indentation level reverts back to the last indentation level at that same column number. Some examples of different indentation levels are shown below:
# Column labels:
# A B C D
...
# Indentation level N:
if a < b
# Indentation level N + 1:
if c < d
# Indentation level N + 2:
e := f
else # Indentation level N + 1
# Indentation level N + 2 again:
# Note that it does not line up
# with previous N + 2 level.
# This ugly but legal.
g := h
# Indentationl level N again:
i := j
The first indentation level occurs for lines in column A. The second indentation level occurs for lines in column B. The third indentation level ocurrs in column C for the first occurance and in level D in the second occurance. While this legal µCL code, it is strongly urged that you be consistent with indentation levels. Having each indentation level vary by 4 columns is the recommended style.
The C, C++, and Java programming languages use braces ({ = code 123 decimal and } = code 125 decimal) to indicate statement and declaration nesting. For programmers who type in braces without even thinking, the µCL language permits braces and semi-colons to be inserted into valid µCL programs. The µCL language ignores these characters except for computing column positions for indentation levels. Thus, the following code fragment is also legal µCL program.
if (a < b) {
return a;
} else {
return b;
}
µCL does not attempt to verify that the braces match. No further examples in this language use either braces or semicolons.
In µCL, a program is first broken into a sequence of tokens. Each token is one of the following catagories:
In µCL, a symbol is a sequence of letters ('A'-'Z', 'a'-'z'), digits ('0'-'9'), dollar sign ('$'), and underscore ('_'). The followining restrictions are in place:
As a point of clarification, a letter includes the standard ASCII letters in addition to the Latin-9 letters with embedded punctuation.
Some examples of good symbols are listed below:
a
Z
$c
bunny
StartHere
start_here
test1
Some examples of bad symbols are listed below:
_Special_ # Starts (and ends) with underscore
Micro$oft # Dollar sign in middle
Bad__news # Two underscores in a row
1potato # Starts with digit
By convention, system libraries will tend to define symbols that start with a dollar sign ('$'). This allows µCL programmers to freely pick names without having to worry about accidentally conflicting with a system library symbol.
µCL supports decimal, hexadecimal, and floating point numbers, character constants, and string constants.
A decimal number consists of one or more decimal digits ('0' through '9') inclusive. Some example decimal numbers are shown below:
0
1
9
12
1234567
A hexadecimal number starts with a "0x" or "0X
" prefix. The prefix is followed by one or more hexadecimal digits
('0'-'9', 'A'-'F', and 'a'-'f'.) Some example hexadecimal numbers are
shown below:
0x0
0x1
0x9
0xa
0xA
0xf
0xF
0xf12
0xABE
{Floating point is coming, but it has not been implemented yet. Thus, nothing in this section, 2.2.2.3, acutally works yet.}
A floating point number constant is a decimal number with a decimal point ('.' = 46 code decimal) character in it optionally followed by an exponent in "e" notation. "E" notation is the letter 'e' or 'E' followed by an optional sign, '+' or '-', followed by a decimal number.
0.
.0
0.0
1.
1.2
1.2345
123.45
.1e-6 # .1×10-6
1.23E-12 # 1.23×10-12
9.87E8 # 9.8×108
Please note that 1e9 is not a valid floating point
constant because there is no decimal point in the first number (i.e.
the mantissa.)
String constants are enclosed in double quotes ('"' = code 34 decimal.) Only printing characters and spaces are allowed between the quote characters. A pair of backslash characters ('\' = code 92 decimal) embedded in the string is used to delineate the non-printing characters. The non-printing characters can be expressed as decimal numbers, hexadecimal numbers, or symbolic names. Mulitple non-printing characters have their number separated by a comma. The symbolic names come from the table below:
Symbol Value Symbol Value Symbol Value Symbol Value Symbol Value nul 0 ht 9 dc2 18 esc 27 t 9 soh 1 lf 10 dc3 19 fs 28 n 10 stx 2 vt 11 dc4 20 gs 29 v 11 etx 3 ff 12 nak 21 rs 30 f 12 eot 4 cr 13 syn 22 us 31 r 13 enq 5 so 14 etb 23 sp 32 tab 8 ack 6 si 15 can 24 del 127 bsl 92 bel 7 dle 16 em 25 a 7 dq 34 bs 8 dc1 17 sub 26 b 8 sq 39
The symbols in the table come mostly from the ASCII control code symbols. The single letter codes are from the escape codes used in C and C++. The last three codes are used to encode backslash (bsl = '\'), single quote (sq = "'") and double quote (dq = '"'.) Some string constant examples are shown below:
"" # Empty string
"a" # String containing single letter "a"
" " # String containing single space
"Hello, World!\n\" # "Hello, World" followed by line feed
"No.\tab\Desc.\lf\" # String with tab and line feed in it
"\bsl\" # String containing single backslash
"'" # String containing single quote.
"\sq\" # String containing single quote
"\dq\" # String containing double quote
"\dq\Hi\dq\" # String encloses "Hi" in double quotes
"Done!\10,13\" # String followed by CR and LF
"Done!\r,n\" # String followed by CR and LF
"Done!\cr,lf\" # String followed by CR and LF
Character constants are just like string constants except that they are enclosed in single quotes and they must contain a single character. Some character constant examples are shown below:
'a' # The letter 'a'
' ' # A space
'\tab\' # A tab
'©' # A Latin-9 copyright '©'
The following tokens are used in µCL as binary operators:
Symbol Usage Symbol Usage Symbol Usage +Addition <Less Than <<Shift Left -Subtraction <=Less Than or Equals >>Shift Right *Multiplication =Equals ~Concatenate /Division !=Not Equals &&Conditional AND %Remainder >Greater Than ||Conditional OR &Bitwise AND >=Greater Than or Equals ,Expression Separate |Bitwise OR @Bit Selection ^Bitwise XOR :=Assignment
The following tokens are used as unary operators:
Symbol Usage +Positive -Negative ~Bitwise NOT !Logical NOT
The remaining tokens are:
Symbol Usage Symbol Usage Symbol Usage (Open Parenthesis )Close Parenthesis ?Arithmetic If [Open Bracket ]Close Bracket :Arithmetic If
A comment line starts with a sharp (# = code 35
decimal) character and goes until the end of line. All characters from
the sharp character to the end of line are ignored by the µCL language.
A comment can be placed at the end of any line. Some examples of
comments are listed below:
# This is a one line comment followed by an empty line
# This a sequence of comments that spans a total of
# three lines. Each line is technically treated
# as an independent comment by the compiler.
global x float24 # A comment after a declaration.
Sometimes an expression gets too long to conveniently fit on one line in the editor. Such an expression can be broken into multiple continuation lines using the following rules:
Some examples should help clarify things.
Example 1:
if a * b > c &d + e < f || # Cont. line 1
g != 0 &h /g > 0 # Cont. line 2
a := a + 1
In this example, the if statement expression is broken across two lines. The first line ends in '||' which tells the compiler to look at the next line for the rest of the expression.
Example 2:
call long_procedure_name( # Cont. line 1
expression1, # Cont. line 2
expression2) # Cont. line 3
In this example, the call statement is broken across three lines. The open parenthesis ('(') after 'long_procedure_name' indicates that the first line is continued onto the second. The second line ends in a comma (',') which indicates that the second line continues to the third line. The third line ends in a close parenthesis (')') which is one of the two punctuation characters that does not force a continuation line.
Here are some examples of bad continuation lines:
Example 3:
call long_procedure_name(
expression1, expression2)
In this example, the first line ends in an open parenthesis ('('), but the second line is not indented by more than the first line.
Example 4:
call long_procedure_name(
expression1,
expression2)
In this example, second and third lines are not indented by the same amount.
The µCL language supports the following basic types:
In addition, µCL supports linear arrays of these types.
A bit can contain the values `0' and `1'. Bits can be stored in variables and transfered via assignment statements.
Some examples of bit code are shown below:
local a bit
local b bit
local c bit
a := 1
b := c
c := a &c # a AND c
a := !b # NOT b
The unsigned integer types are listed in the table below:
Name Precision Lowest Value Highest Value Status byte8 Bits 0 255 Implemented unsigned88 Bits 0 255 Unimplemented unsigned1616 Bits 0 65535 Unimplemented unsigned2424 Bits 0 16777215 Unimplemented unsigned3232 Bits 0 4294967295 Unimplemented
The types byte and unsigned8 can be used
interchangeably. On an 8-bit microcontroller, arithmetic using the
higher precisions takes more cycles to compute. Currently only
byte is implemented.
Some example code with bytes is shown below:
variable a byte
variable b byte
variable c byte
a := 23
b := a
c := a + b << 3
The signed integer types are listed in the table below:
Name Precision Lowest Value Highest Value Status signed88 Bits -128 +127 Unimplemented signed1616 Bits -32769 +32768 Unimplemented signed2424 Bits -8388608 +8388607 Unimplemented signed3232 Bits -2147483648 +2147483647 Unimplemented
None of these types are currently implemented.
The floating point type is listed in the table below:
Name Precision Largest Number Smallest Number Digits of Accuracy Status float3232 Bits ±1038 ±10-38 ~7 Unimplemented
Notice that float24 and float32 can
represent the same sized numbers; however, the number of digits of
accuracy varies. Lastly, the floating point arithmetic operations are
significantly slower on the 8-bit microcontrollers. The libraries that
implement the operations take up a substantial amount of code space.
In µCL, a string is a read only string that is stored in program memory; strings can not be modified.
local text string
local chr byte
local length byte
text := "A string literal" # String assignment
chr := text[3] # chr = 't'
length := text.size # length = 16
Any type can be put into an array. Arrays have a fixed size. The array can be indexed into with a byte (i.e. unsigned8) index value. There is no bounds checking when accessing a byte array. The code below shows some examples array types.
Some sample code with byte arrays is shown below:
global buffer[10] array[byte] # Ten byte buffer
global index byte
global size byte
index := buffer.size - 4
buffer[0] := 0
buffer[index] := 8
buffer[index + 1] := buffer[index]
buffer[23] := 17 # Out of bounds!
size := buffer.size
{more here}
All declarations occur at the outer most level in a program. With
the exception of the procedure declaration, all
declarations are listed in alphabetical order in the following
sections.
bind Declaration The bind declaration has three different forms:
- Simple
bindDeclaration- Defines a new variable that is equivalant to a previously defined global variable or register.
- Array
bindDeclaration- Defines a new variable that is equivalent to a specific entry in a global array.
- Bit
bindDeclaration- Defines a new bit variable that is equivalent to a specific bit in a previously defined global variable or register.
All three forms define a new variable that is in some way equivalent to a previously defined variable.
bind
Declaration A simple bind delcaration has the following form:
bindnew_name=old_name
where
- new_name
- is the new symbol name, and
- old_name
- is a previously defined
registerorglobalvariable.
After a simple bind declaration, new_name is a
variable that is equivalent to old_name.
For example, for the following declarations:
global a byte
register b = 0x88
bind aa = a
bind bb = b
the following are equivalant:
Original Equivalent a := 17aa := 17b := 17bb := 17c := a + 1c := aa + 1c := b - 1c := bb - 1
where c is a simple global byte variable (e.g.
global c byte.)
bind
Declaration An array bind declaration has the following form:
bindnew_name=array_name[constant_expression]
where
- new_name
- is the new symbol name,
- array_name
- is a previously defined
register_arrayorglobalarray, and- constant_expression
- is a constant expression.
After an array bind declaration, the new variable is
equivalent to the specified array location.
For example:
global state[12] array[byte]
bind command = state[0]
bind temporary = state[1]
...
bind last = state[11]
defines a bunch of variables that live in an array of bytes. The following statements are equivalent:
Original Equivalent state[0] := 17command := 17state[1] := 17command := 17state[11] := 17last := 17c := state[0] + 1c := command + 1c := state[1] - 1c := temporary - 1c := state[11] & 1c := last & 1
where c is a simple global byte variable (e.g.
global c byte.)
bind
Declaration The bit bind declaration has the following form:
bindnew_name=old_name@constant_expression
where
- new_name
- is the new symbol name,
- old_name
- is a previously defined
registerorglobalvariable, and- constant_expression
- is a constant expression that evaluates to a value between 0 and 7.
A new variable called new_name is defined that is equivalent to the specified bit expression.
For example,
register $intcon 0xb
bind $gie $intcon @ 7
bind $eeie $intcon @ 6
bind $t0ie $intcon @ 5
bind $inte $intcon @ 4
bind $rbie $intcon @ 3
bind $t0if $intcon @ 2
bind $intf $intcon @ 1
bind $rbif $intcon @ 0
defines the various interrrupt enable bits for the $intcon
register for the PIC16F84. For example the following statements are
equivalent
Original Equivalent $intcon@7 := 1$gie := 1$intcon@4 := 0$inte := 0$intcon@1 := 0$intf := 0
code_bank
Declaration The code_bank declaration has the follow form:
code_bank constant_expression
where
- constant_expression
- is an constant expression that evaluates to a valid code bank (typically between 0 and 3.)
This declaration specifies that until further notice, all
procedure declarations are to be located in the specified code
bank.
For example,
code_bank 0
procedure interrupt
...
code_bank 3
procedure main
...
causes the procedure named interrupt to be placed into
code bank 0 and the procedure named main to be placed into
code bank 3.
configure
Declaration The form of the configure declaration is as follows:
configureoption_name=option_value,...
where
- option_name
- is a valid configuration word option name,
- option_value
- is a valid value for the specified configuration option.
This declaration is used to specify the various configuration options required to set up the microcontroller configuration word (or words.)
For example, the configure declarations below set up the configuration options for a PIC16F767:
configure cp=off, cpmx=rc1, debug=off, borv=borv00, boren=off
configure mclre=off, pwrte=off, wdte=off, fosc=hs
configure borsen=off, ieso=off, fcmen=off
Note that configuration options can be changed. Thus, the initial default configuration options can be defined in a library file and the main program can subsequently override them. The options in effect at the end the program are the ones that are actually output to the final output file.
The valid configuration options are listed under the processor
declaration. Thus, all configure declarations must occur
after the processor declaration.
constant
DeclarationThe constant declaration has the following form:
constantnew_name=constant_expression
where
- new_name
- is the name of the constant, and
- constant_expression
- is a expression that evaulates to a constant value.
Some example constant declarations are shown below:
constant crystal_speed = 20000000
constant instructions_per_second = crystal_speed / 4
constant prefix = "Hello "
constant george = prefix ~ "George"
constant alice = prefix ~ "Alice"
constant bottom = -$u2i(8)
constant pi = 3.14151926
constant pi2 = pi / 2.0
note that the constants can be either numerical or string (i.e. string concatenation.)
The constant declarations are evaluated in sequence. No forward references to constants that are defined later on are permitted.
data_bank
Declaration The data_bank declarations has the following form:
bank constant_expression
where
- constant_expression
- is the register bank to select.
Some microcontrollers have more than one bank of memory (e.g. the
PIC1687x). The data_bank declaration is used to select
which memory bank to allocate subsequent variables from.
The programmer is responsible for ensuring that the memory within a given bank are not exhausted. The compiler will generate an error message if the number of registers within a given bank are exhausted.
The compiler is responsible for generating the additional data bank select instructions for accessing variables that located in various different memory banks.
debug Declaration The debug declaration has the following form:
debugprocedure_name,...
where
- procedure_name
- is the name of a procedure.
The declaration declares the procedures for which
additional debugging code will be inserted. Each procedure listed in a
debug declaration can support break points when being used by the
µCL integrated programming environment.
icd2 Declaration The form of the icd2 declaration is as follows:
icd2
This declaration tells the compiler to use the various configurations needed for Microchip In Circuit Debugger 2. Obviously, this declaration is extremely specific to the microchip product line.
icd2_configure
Declaration The form of the icd2_configure declaration is as
follows:
icd2_configureoption_name=option_value,...
where
- option_name
- is a valid configuration word option name,
- option_value
- is a valid value for the specified configuration option.
This declaration is used to specify the various configuration options required to set up the microcontroller configuration word (or words) for the Microchip ICD2. This declaration is very specific to the Microchip product line.
For example, the ICD2 configure declarations below set up the configuration options for a PIC16F767:
icd2_configure cp=off, cpmx=rc1, debug=on, borv=borv00, boren=off
icd2_configure mclre=off, pwrte=off, wdte=off, fosc=hs
icd2_configure borsen=off, ieso=off, fcmen=off
{Note: Fix compiler to use this declaration.}
global Declaration
There are two related forms for the global declaration:
- Simple
globalDeclaration- This declares a simple global variable
- Array
globalDeclaration- This declares a global array.
The defined global variable is accessible from all procedures.
global
Declaration A simple global declaration has the following form:
global variable_name
variable_type
where
- variable_name
- is the name of the new global variable, and
- variable_type
- is the type of the new global variable.
For example,
global trace bit
global command byte
...
procecdure main
...
if trace
call $uart_byte_print(command)
trace := 0
shows the definition of two global variables, trace and
command, where the first is of type bit and
the second is of tyhpe byte. Later on in the procedure
main, both trace and command are
accessed.
global
Declaration The array global declaration has the following form:
globalarray_name[size_expression]array [simple_type]
where
- array_name
- is the variable name for the global array,
- size_expression
- is an expression that evaluates to a constant that specifies the array size, and
- simple_type
- is the type of each element in the global array. Currently, only
byteis allowed.
The defined global variable is an array that is accessable from all procedures.
For example,
global buffer[16] array[byte]
global buffer_in byte
...
procecdure main
...
variable datum byte
...
buffer_in := buffer_in & 0xf
buffer[buffer_in] := datum
shows the definition of the global variable buffer
which is an array of 16 bytes. Later on in the main
procedure, datum is stored into buffer.
library Declaration
The library declaration has the following form:
library library_name
where
- library_name
- is the name of the library to use with the program.
All of the declarations from the library file are included into the main program.
A library named my_library will have a file name of
my_library.ucl. A library file can reside in either the µCL
system directory/folder, or in the directory/folder that contains the
main program. If a file with the same name resides in both
directories/folders, the compiler will complain about the ambiguity and
refuse to load either one. {Actually, I've been burned by this several
times, and I need to add the test!}
When it comes to constant declarations that reside in
an µCL library, care must be taken to ensure that there are no forward
references. Thus, if constant1 is defined in
library1 and constant2 is defined using
constant1 in library2, library1 must be
referenced before library2.
# In library1.ucl:
...
constant constant1 = 1
...
# In library2.ucl:
...
constant constant2 = constant1 * 3
...
# In main.ucl:
...
library library1 # Defines constant1
library library2 # Defines constant2
By convention, library names that start with a dollar sign ('$') are system libraries and library names that do not start with a '$' are user supplied libraries. By convention, system libraries should only define symbols with a dollar sign in them in order to avoid conflicts with user supplied symbols.
Some example code using the library declarations is shown below:
library $pic16f767 # System definitions for PIC16F767
library navigate # User navigation package
The library $pic16f767 contains a whole slew of
constant and bind declarations that declare symbols
that start with a `$'. The librarynavigate is
a user library where symbols start with the letters 'a'
through 'z'.
Libraries can recursively reference other libraries. Thus, the
library $pic16f767 loads the library $pic16f7x7
.
The compiler will only load a library once. If a library is referenced a second time, the compiler silently ignores the second load request. For those of you who know what the word idempotent means, µCL libraries are idempotent.
µCL libraries can contain procedure declarations. The
compiler delays producing code for these loaded procedures until after
it has produced code for the main procedures. The library_bank
declaration allow you to load libraries into different code banks.
library_bank
Declaration The library_bank declaration has the following form:
library_bank bank_expression
where
This declaration specifies that any procedures loaded from a library will be loaded into the bank_expression code bank.
For example,
...
library_bank 2
library $float32
library_bank 3
library $trig
origin Declaration
The origin declaration has the following form:
origin constant_expression
where
- constant_expression
- is the a constant expression that specifies where subsequently generated code is to be placed.
The origin declaration is used to retarget code
placement.
For microcontrollers that have the concept of code banks (e.g. the PIC1687x), the origin declaration uses the high order bits of the origin to implicitly set the code bank. It is up to the programmer to manage the placement of procedures within code banks using the origin declaration. The compiler will generate an error if the procedures within a given code bank spill over into another code bank.
The compiler is responsible for generating the appropriate additional instructions for placing calls from procedures in one code bank to procedures in a different code bank.
package Declaration
The package declaration has the following form:
packagename=> pin_declarations ... <=
where
- name
- is the name of the desired package, and
- pin_delcarations
- is an indented list of
pindeclarations.
The package declaration selects which integrated
circuit package is being used for a particular microcontroller project.
The subsequent nested pin declarations further identify
how the various pins on the microcontroller are being used. Using this
information, the compiler generates the appropriate initialization code
for specified pin usages.
Many microcontrollers are supplied more than one package (e.g. DIP,
SOIC, SSOP, etc.) For example, the PIC16F87 comes in an 18-pin dual
in-line package (DIP), an 18-pin small outline integrated circuit
(SOIC), a 20-pin small shrink outline package (SSOP), and a 28-pin quad
flat no leads package (QFN). When you select a particular package for
your project, the package declaration helps capture the
relevant information about how the package is being used.
pin Declaration The pin declarations has the following form:
pinpin_number=pin_usage,new_name=usage,...
where
- pin_number
- is the decimal pin number being selected,
- pin_usage
- is the pin usage,
- name
- is a new variable or constant, and
- usage
- is one of
name,bit, ormask.
Everything up to the first comma is required; everthing from the
comma onwards is optional. The pin_number and pin_usage
must match the corresponding information in the processor
declaration. If they do not match, the compiler generates a fatal
error.
The table below summarizes what happens for name,
bit, and mask binding:
pinSyntaxIs Equivalent To new_name = namebindnew_name=port_name@bit_numbernew_name = bitconstantnew_name=bit_numbernew_name = maskconstantnew_name=1 << bit_number
package Example The example below shows an example of a package
declaration:
library $pic16f676
package pdip
pin 1 = power_supply
pin 2 = clkin
pin 3 = an3
pin 4 = mclr
pin 5 = rc5_out, name=coil0a, mask=coil0a_mask
pin 6 = rc4_out, name=coil0b, mask=coil0b_mask
pin 7 = rc3_out, name=coil1a, mask=coil1a_mask
pin 8 = rc2_out, name=coil1b, mask=coil1b_mask
pin 9 = rc1_in, name=step
pin 10 = rc0_in, name=dir
pin 11 = ra2_in, name=mode
pin 12 = ra1_in
pin 13 = an0
pin 14 = ground
In this example, the microcontroller being used is the PIC16F676.
The processor declaration is in the $pic16f676
library. The 14-pin plastic DIP (pdip) package is being
used for this particular project. Pin 1 and 14 are used for the power
supply and ground respectively. Pin 2 is used as an oscillator input
and pin 4 is used for master clear. Pins 5 through 8 are used as
digital outputs on port C bits 2 through 5. Pins 9 through 12 are
digital inputs on port C bits 0 and 1 and port A bits 1 and 2. Pin 3
and 13 are analog inputs for A/D selects of 0 and 3. All of the digital
I/O pins are given names (i.e. coil0a, coil0b
, coil1a, coil1b, step, dir
, and mode.) The digital output pins also have bit masks
defined (i.e. coil0a_mask, coil0b_mask,
coil1a_mask, coil1b_mask.) As you can see, there is
quite a bit of documentation about the project embedded into the
package declaration.
processor
Declaration The package declaration has the following form:
processorname=> processor_declarations ... <=
where
- name
- is the processor name, and
- processor_delcarations
- is an indented list of processor declarations.
The processor_declarations are listed in alphabetical order in the sections that follow.
code_bank
Declaration The code_bank declaration has the following format:
code_bankstart_address:start_address
where
- start_expression
- is the address of the first instruction location in the code bank, and
- end_expression
- is the address of the last instruction location in the code bank.
This declaration specifies the starting address and ending address of one code bank for the processor. For the PIC16 series of processors, most code banks are 2K words in size.
configure_address Declaration The configure_address declaration has the following
format:
configure_address address_expression
where
- address_expression
- is a constant expression that specifies the address in the Intel Hex file at which the configuration word is located.
The address specified by this declaration is used by all following
configure_fill and configure_option declarations.
A configure_address declaration can occur more than
once. Each configure_address declaration remains in effect
until superceeded by the next configure_address
declaration. Multiple configure_address declarations are
only needed for microcontrollers that have more than one configuration
word (e.g. the PIC16F7x7 series.)
configure_fill
Declaration The configure_fill declaration has the following
format:
configure_fill fill_mask_expression
where
- fill_mask_expression
- is a constant expression of a value that is always OR'ed into the current configuration word.
This declaration is used to set one or bits of the current configuration word to a 1.
configure_option Declaration The configure_option declaration has the following
format:
configure_optionfield_name:option_name=option_value
where
- field_name
- is the name of the configuration word field that is being specified,
- selection_name
- is the name of the configuration selection, and
- option_value
- is a constant expression that specifies what bits to OR into the configuration word if selected.
Each configuration_option specifies a possible value
for a configuration word field. The configure declaration
is used to set up the configuration word (or words) for project.
data_bank
Declaration The data_bank declaration has the following format:
data_bankstart_address:end_address
where
- start_address
- is the address of the first memory address in the data bank, and
- end_address
- is the address of the last memory address in the data bank.
This declration specifies the first and last addresses of a processor data bank. For the PIC16 series of microcontrollers, data banks are typically 128 bytes in size.
global_region
Declaration The global_region declaration has the following format:
global_regionstart_address:end_address
where
- start_address
- is the address of the first memory address of a global memory region, and
- end_address
- is the address of the last memory address of the same global memory region.
The compiler uses a global region to allocate variables from (i.e. global variables, procedure arguments, local varaibles, temporary variables, etc.)
icd2_global_region Declaration The icd2_global_region declaration has the following
format:
icd2_global_regionstart_address:end_address
where
- start_address
- is the address of the first memory address of a global memory region, and
- end_address
- is the address of the last memory address of the same global memory region.
The compiler uses a global region to allocate variables from (i.e. global variables, procedure arguments, local varaibles, temporary variables, etc.) When the In Circuit Debugger 2 is enabled, this global region is used for allocation instead.
icd2_shared_region Declaration The icd2_shared_region declaration has the following
format:
icd2_shared_regionstart_address:end_address
where
- start_address
- is the address of the first memory location where is sharable across multiple data memory banks, and
- end_address
- is the address of the last memory location where is sharable across multiple data memory banks.
This declaration identifies a region of shared variables to be used when the In Circuit Debugger 2 (ICD2) is enabled.
interrupts_possible Declaration The interrupts_possible declaration has the following
format:
interrupts_possible
When this declaration is present, it specifies that interrupts are
supported by the microntroller. Thus, an interrupt procedure named
interrupt is allowed.
osccal_at_address Declaration The osccal_at_address declaration has the following
format:
osccal_at_address address_expression
where
- address_expression
- is the address address at which the oscillator callibration RETLW instruction is located.
Some of the PIC16 microcontrollers store an osscillator callibration value in program memory as a RETLW instruction. This declaration informs the compiler that the currently defined processor does this and where in program memory the RETLW instruction is located.
osccal_in_w
Declaration The osccal_in_w declaration has the following format:
osccal_in_w
When this declaration is present, it specifies that the oscillator callibration value is loaded into the W register at the beginning of processor start up. The compiler will take this value and stuff it into the appropriate oscillator callibration register.
osccal_register_symbol Declaration The osccal_register_symbol declaration has the
following format:
osccal_register_symbol
osccal_register_name
where
- osccal_register_name
- is the name of the oscillator callibration register.
The compiler uses this register name when generating code for the
osccal_in_w or oscal_at_address declaration.
packages
Declaration The packages declaration has the following format:
packagespackage_name=number_of_pins,...
where
pin Declaration The pin declaration has the following format:
pinpin_usage,...=> pin_declarations ...
where
- pin_usage
- is the name an acceptable pin usage for the pin, and
- pin_declarations
- is an indented list of pin declarations.
The various pin_declarations are listed alphabetically in the sections below.
bind_to
Declaration The bind_to declaration has the following form:
bind_toport_name@bit_number
where
- port_name
- is the name of the port associated with the pin, and
- bit_number
- is the bit number in the port associated with the pin.
or_if
Declaration The or_if declaration has the following form:
or_if pin_usage register_name
or_value
where
- pin_usage
- is one of the pin usage names listed by the
pindeclaration one level up,- register_name
- is a register name to OR an initalization value into, and
- or_value
- is the value that is value that is OR'ed in.
pin_bindings
Declaration The pin_bindings declaration has the following form:
pin_bindingspackage_name=pin_number,...
where
- package_name
- is a valid package name, and
- pin_number
- is the pin number assoicated with the pin for the specified package.
{more goes here}
shared_region
Declaration The shared_region declaration has the following format:
shared_regionstart_address:end_address
where
- start_address
- is the address of the first memory location where is sharable across multiple data memory banks, and
- end_address
- is the address of the last memory location where is sharable across multiple data memory banks.
processor Example
An example processor declaration for the 8-pin
PIC12C675 is shown below:
processor pic12f675
The name of the processor, pic12f675, immediately
follows processor.
configure_address 0x2007 configure_fill 0x0
Next, the configuration word is declared. There is one configuration
word that is at address 0x2007 as specified by the
configuration_address declaration. The configuration word has 8
fields starting with bg through fosc. While 3
bits of the configuration word are unimplemented, the microcontroller
specification sheet says that they should be written as zeros; thus,
configuration_fill is set to 0.
configure_option bg: bg11 = 0x3000 configure_option bg: bg10 = 0x2000 configure_option bg: bg01 = 0x1000 configure_option bg: bg00 = 0x0000 configure_option cpd: on = 0x000 configure_option cpd: off = 0x100
Only 2 fields are shown to keep the example size down. The bg
field has four possible values of bg11, bg10,
bg01, and bg00 with configuration word mask
values of 0x3000, 0x2000, 0x1000, and 0 respectively. The cpd
field has two possible values of on and off
with values of 0x000 and 0x100 respectively.
code_bank 0x0 : 0x3ff
There is one code bank of 1024 (0x400) words in size.
data_bank 0x0 : 0x7f
data_bank 0x80 : 0xff
There are two data banks, where the first data bank is from 0 through 0x7f and the other is from 0x80 through 0xff.
shared_region 0x20 : 0x5f
This microcontroller is a little strange because all of its memory
is accessible from both data banks. Thus, there are no
global_region declarations.
interrupts_possible
This microcontorller supports interrupts.
osccal_register_symbol $osccal
osccal_at_address 0x3ff
The oscillator callibration value is stored as a RETLW instruction
at program memory address 0x3ff as spciffied by the
osccal_at_address. The register that contains the oscillator
callibration value is $osccal as specified by the
osccal_register_symbol declaration.
packages pdip=8, soic=8, dfn_s=8
This microcontroller comes in 3 different packages -- pdip
, soic, and dfn_s. All three packages have 8
pins each.
pin vdd, power_supply
pin_bindings pdip=1, soic=1, dfn_s=1
The power supply pin is called either vdd or
power_supply. It is located on pin 1 for all three packages as is
listed in the pin_bindings declaration.
pin gp5_in, gp5_out, t1cki, osc1, clkin, gp5_unused
pin_bindings pdip=2, soic=2, dfn_s=2
bind_to $gpio@5
or_if gp5_in $trisio 16
or_if gp5_out $trisio 0
or_if t1cki $trisio 16
or_if osc1 $trisio 16
or_if clkin $trisio 16
or_if gp5_unused $trisio 16
The GP5 pin can be called gp5_in, gp5_out,
t1cki, osc1, clkin, or
gp5_unsused. The pin_bindings declaration binds
these names to pin 2 on all three packages. When used as a digital
input or output, the pin is connected to bit 5 of the $gpio
register as specified by the bind_to declaration. The six
or_if declarations specify what value to OR into the
$trisio register depending upon how the pin is used. In general,
by setting the $trisio bit 5 to a 1, sets it as an input.
Only when gp5_out is specified, does the $trisio
bit 5 get set to 0.
As you can see there a a lot of information to specify for each new microcontroller, but once it is specified, the end-user does not need to be worry about it.
register
Declaration The register declaration has the following form:
registername=address,...
where
- name
- is the name of the register, and
- address
- is a memory address that accesses the register. There can be multiple addresses for those registers that accessible from different data memory banks.
An example of some register delcarations is listed
below:
register $indf = 0, 0x80
The $indf register is accessible from both data memory
banks at address 0 and 0x80.
register $tmr0 = 1
The $tmr0 register is accessible from the first memory
bank at address 1.
register $pcl = 2, 0x82
register $status = 3, 0x83
Both the $pcl and $status registers are
accessible from both memory banks.
register_array
Declaration The register_array declaration has the following form:
register_array name start_address
size_expression
where
- name
- is the name of the register array,
- first_constant_expression...
- is a constant expression that evaluates to the address of the first register, and
- size_expression
- is a constant expression that specifies how many registers are in the array.
The register_array specifies an array of bytes at
specific address for a specific size. Frankly, it is kind of a hack and
I need to figure out a better way of accomplishing the task.
string Declaration
The string declaration has the following form:
stringstrings_name=string_expression
where
- strings_name
- is a name of the string, and
- string_expression
- is the value of the string.
This declaration defines a global string that can accessed from any procedure.
The following example shows a string declaration and
some code that access the string:
...
string hello = "Hello world!\cr,lf\"
...
procedure main
...
local index byte
...
index := 0
loop_exactly hello.size
call $uart_byte_put(hello[index])
index := index + 1
...
The string hello is declared to have a value of
"Helloworld!\cr,lf\" in the string declaration.
Later on, the code prints out the string value using a
loop_exactly loop. The size of the string is accessed via
hello.size. Individual characters are accessed via
hello[index].
ucl Declaration The ucl declaration has the following form:
uclmajor.minor
where
- major
- is the µCL major version number, and
- minor
- is the µCL minor version number.
procedure
Declaration The procedure declaration has the following form:
procedurename=> argument_declarations return_declaration optional_exact_delay_declaration local_declarations statement_declarations ... <=
where
- name
- is the procedure name,
- arguement_declarations
- is either an
arugments_nonedeclaration or one or moreargumentdeclarations,- return_declaration
- is either a
returnsdeclaration, orreturns_nothingdeclaration,- optional_exact_delay_declaration
- is an optiona
exact_delaydeclaration,- local_declarations
- is one or more
localvariable declarations, and- statement_declarations
- is one or more statement declarations.
Everything after the first line is indented by one level.
There are currently two special procedure names -- main
and interrupt. The main procedure is the
where program execution starts. The compiler places register
initialization code into the beginning of the main
procedure. The interrupt procedure is called each time an
interrupt occurs. The compiler adds code to save and restore both the W
and status registers for the interrupt procedcure.
{Eventually, it will save and restore the FSR register as well.}
argument
Declaration The argument declaration has the following form:
argument name type
where
- name
- is the argument name, and
- type
- is the argument type -- currently one of
bitorbyte.
There is one argument declaration for each procedure
argument passed in.
arguments_none
Declaration The arguments_none declaration has the following form:
arguments_none
This specifies that the procedure has no arguments.
exact_delay
Declartion The exact_delay declaration has the following form:
exact_delay cycles_expression
where
- cycles_expression
- is the exact number of processor that the procedure should take.
This declaration that takes exactly cycles_expression cycles to execute. This means that conditional code generated for `if', `and `||' will be padded with NOP instructions to ensure that each path taken through the code takes exactly the same number of instruction cycles.
local Declaration The local declartion has two possible forms:
- Simple
localDeclaration- This form defines a simple local variable. Currently, on type of
bitandbyteare supported.- Array
localDeclaration- This form define a local array variable. Currently, only an array of bytes is supported.
local
Declaration The simple local declaration has the following form:
local name type
where
- name
- is the local variable name, and
- type
- is the local variable type -- currently one of
bitorbyte.
All local declaration defines a variable that is local
to the procedure body. It is not possible for one procedure to directly
access the local variables of another procedure. There are no nested
variables in this language.
local
Declaration The array local declaration has the following form:
localname[size_expression] array [type]
where
- name
- is the local array variable name,
- size_expression
- is the array size, and
- type
- is the type of each array element. Currently, only of
byteis supported.
All `variable' statements defines a variable that is local to the procedure body. It is not possible for one procedure to directly access the local variables of another procedure. There are no nested variables in this language. A variable that occures deep within a some nested statements is accessible through out the entire procedure.
returns Statement
The returns declaration has the following form:
returnstype,...
where
- type...
- is the type for each returned value.
This declaration lists one or more return types. Unlike most other programming languages, µCL allows for the return of more than one value from a procedure call.
returns_nothing
Declaration The returns_nothing declaration has the following form:
returns_nothing
This declaration specifies that the procedure returns no values.
Statements can only occur within the body of procedure
declaration. The various statements are listed alphabetically below.
assemble Statement
The assemble statement has the following form:
assemble=> assembly_lines ... <=
where
- assemble_lines
- is a list of assembly statements to insert into the code.
The assembly lines have one of the following forms:
Form Descripton opcode Instruction with no operands opcode operand Instruction with one operand opcode operand1, operand2 Instruction with two operands :labelLabel definition (note that :is before label name)definename=expressionConstant definition
The following instruction opcodes are currently supported:
Opcode Operands Description Operation addlw k ADD k to W W := W + k addwf f, d Add W and f W|f := W + f andlw k AND k to W W := W & k andwf f,d AND W and f W|f := W & f bcf f, b Bit clear f f@b := 0 bsf f, b Bit set f f@b := 1 btfsc f, b Bit test f, skip if clear if !f@b then skip btfss f, b Bit test f, skip if set if f@b then skip call a Call subroutine at a call a() clrf f Clear f f := 0 clrwdt Clear watchdog timer clrwf Clear W W := 0 comf f d Complement f W|f := ~f decf f, d Decrement f W|f := f - 1 decfsz f d Decrement f, skip if 0 W|f := f - 1; if W|f = 0 then skip goto a a Go to address a goto a incf f, d Increment f W|f := f + 1 incfsz f, d Increment f, skip if 0 W|f := f + 1; if W|f = 0 then skip iorwf f, d Inclusive OR W and f W|f := W | f iorlw k Inclusive k to W W := W | k movf f, d Move f W|f := f movwf f Move W to f f := W movlw k Move k to W W := k nop No Operation option Option instruction retfie Return from interrupt retlw k Return from subroutine with k in W W := k ; return return Return from subroutine return rlf f, d Rotate left through carry rrf f, d Rotate right through carry sleep Enter low power mode sublw k Subtract W from k W := k - W subwf f, d Subtract W from f W|f := f - W swapwf f, d Swap nibbles in f W|f := ((f & 0xf) << 4) | ((f >> 4) & 0xf) xorwf f, d Exclusive OR W and f W|f := W ^ f xorlw k Exclusive OR k to W W := W ^ k
The example below shows the assemble statement in
action:
...
procedure left_rotate
argument value byte
returns_nothing
# This procedure will return the value of
# rotation value to the left by 8 bits.
# {value} is sitting in W:
$c := value@7
assemble
rlf left_rotate__value, w
return
This procedure will take an 8-bit byte value and rotate it left in
8-bits. The first statement will set the carry bit ($c) to
the the high order bit of value. The assemble
statement executes an RLF instruction. The full name of the argument is
the procedure name left_rotate, followed by two
underscores __, followed by the argument name value
, resulting in left_rotate__value. The result is in the W
register, so a simple RETURN instruction ends the procedure.
The assignment statement has two possible forms:
- Simple Assignment
- Simple assignment takes the result of an expression and assigns it to a variable.
- Multiple Assignment
- Multiple assignme takes several results from an expression and assigns it to two or more variables.
The assignment statement is unique in that it is the only statement
that does not start off with keyword. Instead, the parser prescans the
line and if it encounters an assignment operator (:=), it
assumes the entire statement is an assignment statement.
The simple assignement statement has the form:
variable := expression
where
- variable
- is either a simple variable or an array variable (e.g. array_name[index_expression]), and
- expression
- is an evaluated expression that is assigned into variable.
The multiple assignement statement has the form:
variable1,...,variablen:=multiple_expression
where
- variablei
- is either a simple variable or an array variable (e.g. array_name[index_expression]), and
- multiple_expression
- is an evaluated expression that that has multiple values.
The type of the variables and expressions must match up.
The following example shows a simple multiple assignment:
procedure main
...
local a byte
local b byte
...
# Swap A and B:
a, b := b, a
Another example is shown below:
procedure $uart_byte_read
argurment usec_wait byte
returns bit, byte
while ...
value := ...
# No time out:
return 0, value
# Time out:
return 1, 0
procedure main
...
local command byte
local time_out bit
...
time_out, command := $uart_byte_read(100)
if time_out
...
else
...
For this code fragment, there is a procedure called
$uart_byte_read that takes a single argument usec_wait
that specifies the maximum wait time for read a byte form the UART
(Universal Asynchronous Receiver Transmitter). If a byte is recevied
before the time out period has elapsed, the time out bit is returned a
0 and the UART value is returned as they byte value. Otherwise, a time
out has occured and the time out bit is returned as a 1 and the value
is returned as 0. Later on in the main procedure,
$uart_byte_read is invoked and its two return values are assigned
to the local variables time_out and command
via a multiple assignment.
call Statement The call statement has the following form:
callprocedure_name(argument_expressions)
where
- procedure_name
- is the name of the procedure to be called, and
- argument_expressions
- is a list of zero, one, or more expressions to be evaulated and passed as arguments to the procedure.
The number and type of each argument expressions must match the procedure types.
The call statement is used to call procedures that have
no return values (i.e. returns_nothing). In addition, the
call statement can be used to invoke a procedure that returns
values, but where the return values are not needed.
delay Statement The delay statement has the following form:
delayexpression=> statements ... <=
where
- expession
- is a constant expression that specifies the exact number of instruction cycles to be to be executed, and
- statements
- is a nested sequence statements that are executed. Each statement in statements is compiled to have uniform execution time. Conditional code, like `if', `and `||', is padded with nop instructions to cause the excution time to be uniform.
Each procedure called in statements must have a
exact_delay declartion in its procedure declaration.
The example below delays for 50 µSec
# 5 cycles per microsecond
constant usec = 5
procedure main
...
# Delay for 50 usec:
delay 50 * usec
do_nothing
delay_set Statement
The delay_set statement has the following form:
delay_setexpression=> statements ... <=
where
- expression
- is a constant expression that sets the delay value that the compiler will use for the nested statements, and
- statements
- is a nested sequence of statements.
This statement is used to tell the compiler exactly how many cycles a give chunk of code is supposed to take.
do_nothing
Statement The do_nothing statement has the following form:
do_nothing
In fact, this statement does not do anything.
if Statement The if statement has the following form:
ifbit_expression=> statements ... <= else_ifbit_expression=> statements ... <= else=> statements ... <=
where
- bit_expression
- is an expression that evaluates to a bit value, and
- statements
- is a nested sequence of statements to be executed if bit_expression evaluates to 1 (i.e. true.)
There can be zero, one or more else_if clauses. The
else clause is optional. The first if clause and its
nested statement block is required.
At most, only one nested statement block is executed. The first
bit_expression that evaluates to 1 (i.e. true) causes the
associated statement block to be executed. If none of the
bit_expression's evaluate to 1, the else clause
statement block is executed (if present.)
loop_exactly
Statement The loop_exactly statement has the following form:
loop_exactlyexpression=> statements ... <=
where
- expression
- is the number of times the expression is executed, and
- statements
- is the nested statement block that is executed each iteration through the loop.
Note that expression must evaluate to a non-zero value. {This is a bogus restriction and needs to be fixed.}
loop_forever
Statement The loop_forever statement has the following form:
loop_forever=> statements ... <=
where
- statements
- is a nested statement block that is continuosly executed.
For embedded applications, the main procedure typically
has a loop_forever statement, since it never makes sense
to return from main.
return Statement The return statement has the following form:
returnexpression,...
where
- expression
- is an expression that is evaluated and returned from the procedure.
The number and type of expressions in the return
statement must match the types in the returns clause for
the enclosing procedure declaration. If the
procedure declaration has a returns_nothing clause,
the return statement must not have any expression.
switch Statement The switch statement has the following form:
switchswitch_expression=> case_maximummaximum_expressioncasecase_expression 1=> statements ... <= ... casecase_expression N=> statements ... <= default=> statements ... <= <=
where
- switch_expression
- is an expression is used to steer the switch,
- maximum_expression
- is a constant expression that specifies the maximum possible value of switch_expression,
- case_expressioni
- is a constant expression, and
- statements
- is a nested statements block.
The switch_body consists of a sequence of one or more case_clause's, followed by an optional default_clause. The expression is evaluated and control is transfered to one of the clauses. Only case_clause's, a default_clause, comments and blank lines can occur inside of switch_body.
An example switch statement is shown below:
switch command >> 5
case_maximum 7
case 0
# First command:
...
case 1, 2
# Second and third commands:
...
case 3
# Forth command:
...
default
# All other commands are undefined:
...
watch_dog_reset
Statement The watch_dog_reset statement has the following form:
watch_dog_reset
This statement generates the code to reset a watch dog timer in a microcontroller.
while Statement The while statement has the following form:
whilewhile_expression=> statements ... <=
where
- while_expression
- is an expression the returns a bit value,
- statements
- is the indented statemenst for the while loop.
This statement will evaluate while_expression and if it evaluates to 1 (i.e. true) it will execute the indented statement block statements. It will do this repeatabley until while_expression evaluates to 0 (i.e. false.)
Expressions in µCL are modeled after expressions in ANSI-C. There are a few differences between µCL expressions and C expressions.
If you do not know C-expressions, you should probably skip reading this section.
The differences from C-expressions itemized below:
This section is for reference purposes for those people who are not familiar with the concept of operator precedence.
In regular arithmetic expressions like `1 + 2 × 3 - 4 ×5 + 6', the `operator has a higher precedence than the `+' and `-' operator. Thus, multiplication and division are performed before addition and subtraction. This can be made more explicit by adding parenthesis as follows -- `1 + (2 × 3) - (4 ×5) + 6'. In many programming languages, there are usually a couple of dozen operators and each of them have different precedences.
As usual, parenthesis are used to change the order operation execution. Thus, `(1 + 2) × (3 - 4) ×(5 + 6)' causes the addition and subtraction to occur before the multiplication.
The sections below list operators in µCL expressions from lowest procedence to highest prcedence. The lowest precedence operators are performed after all higher precedence operators have been done.
:=
)The assigment operator is:
- `:='
- Straight assignment (L := R)
µCL supports multiple assignment. In mulitple assignment, a list of expressions to the right are assigned to a list of variables on the left. All of the expressions to the right are evaluated and stored in temporary varaibles before any of the assignments take place. The example below will swap the contents of the `a' and `b' variables:
a, b := b, a
which is equivalent to:
T1 := b
T2 := a
a := T1
b := T2
where T1 and T2 are temporaries.
Another form of multiple assignment occurs when a procedure returns
more than on value. An example should help clarify this. Let us assume
that the procedure plus_minus(a, b) returns a+b
and a-b. This procedure would be written as follows:
procedure plus_minus
argument a byte
argument b byte
returns byte byte
return a + b, a - b
and we can invoke `plus_minus' as follows:
a_plus_b, a_minus_b := plus_minus(a, b)
The first value returned from plus_minus is a+b
and it is assigned to the variable a_plus_b. The second
value returned from plus_minus is a-b and it
is assigned to the variable a_minus_b.
,) The comma operator , does not perform any computation
per se. All it does is cause other expressions of higher precedence to
be executed in left-to-right order. It is used to separate variables
and expressions in multiple assignment statements (e.g. a, b :=
b, a) and it is used to separate the arguments passed to
procedures.
A lot of C programmers have programmed in C for years without realizing that in C most implementations use right-to-left order of execution. The C language specification does not mandate either left-to-right or right-to-left execution order. However, the first implementations of C pretty uniformly implemented right-to-left execution in order to support variadic (i.e. many variables) functions like `printf'. Pretty much all subsequent C implementations after that have followed the same rule. The order of execution only crops up when the expressions involve side effects. For example, in C:
(void)printf("first:%d second:%d\n", get_byte(), get_byte())
does not do what most people think it does. The first call to `get_byte' is the right-most one followed by the left-most one. Thus, in the example above, the first byte that is read is actually printed as the decimal number next to `second' and vice verce. This is probably not what the C programmer had in mind.
In µCL, execution order is always left-to-right and there are no suprises like there are in C.
||) The expresion L || R returns 1
if either L or R evaluate to 1 It is a
conditional OR because it will not execute R if L
returns a 1.
Consider the code fragment below:
if (denominator = 0 || numerator/denominator = 0) {
# ...
}
In this example, it would erroneous to divide the numerator by zero, so we can check for zero beforehand and only if it is non-zero does the division take place.
If it is desirable to always execute the left and the right side
before computing the OR, the bitwise OR (|) operator can
be used.
&&) The expresson L && R returns 1
if both L and R evaluate to 1. It is a
conditional AND because, it will not bother to execute R if
L returns a 0. Consider the code fragment below:
if (denominator != 0 && numerator/denominator > 0) {
# ...
}
In this example, it would erroneous to divide the numerator by zero, so we can check for zero beforehand and only if it is non-zero does the division take place.
If it is desirable to always execute the left and the right side before computing the AND, the bitwise AND (`&') operator can be used.
The precedence of `&&' is higher than `||'. Thus,
A && B || C && D
would be executed as
(A && B) || (C && D)
As usual, it never really hurts to add parentheses to improve readability.
<, =, >
, <=, !=, >=, @)There is one bit selection operator and six relational operators:
- L
@N- The N'th bit of L.
- L < R
- L less than R
- L = R
- L equal to R
- L > R
- L greater than R
- L <= R
- L less than or equal to R
- L != R
- L not equal to R
- L R
- L greater than or equal to R
The equality operators (= and !=) work for
operands of type byte and bit and all the
other opertators (<, >, <=,
>=, and @) only work for operands of type `byte'.
NOTE: bit equals and not-equals is not imlemented yet. The work
around is quite ugly -- A && B || !A && !B for equality
and A && !B || !A && B for inequality.
It is not permissible to stick an extra space between any of the two
character relational operators (<=, !=, and
>=).
The bit selection operator is not present in C and is unique to µCL.
A @ N is the N'th bit of A
. Both A and N must be of type byte. The
result is of type bit. A@0 selects the least
significant of A. B@7 selects the most
significant bit of B.
NOTE: Currently, the right operator of bit selection must be a
constant. A reasonable work around would be A & 1 << N != 0
which is grouped as (A & (1 << N)) != 0; unfortunately,
1<<N where N is not a constant is also
unimplemented. Sigh.
C programmers should note that the equality operator consists of a
single = not the double == used in C.
In C, the char type usually stands for a byte. The
ANSI-C standard allows char to be either signed
or unsigned. This ambiguity causes all sorts of grief when
porting C code between C compilers. There is no such ambiguity in µCL,
the byte type is always represents non-negative numbers
between 0 and 255 inclusive. Thus, in µCL, 128 is always
greater 127 whereas in C (char)128 is
sometimes less than (char)127 and sometimes greater.
The precedence of the relation operators is greater than both
conditional AND (&&) and conditional OR (||).
Thus, the following code fragment
0c'a' <= c && c <= 0x'z'
is grouped as
(0c'a' <= c) && (c <= 0x'z')
+, -) The addition operator is + and the subtraction operator
is -. These operators are only defined for expressions of
type byte. The order of execution is strictly left to
right. Thus,
a + b - c + d
is evaluated as:
((a + b) - c) + d
Currently, µCL does not implement 16-bit or 32-bit arithmetic. You can use the following work-around:
variable a_lo byte
variable a_hi byte
variable b_lo byte
variable b_hi byte
variable c_lo byte
variable c_hi byte
c_hi := a_hi + b_hi
c_lo := a_lo + b_lo
if $c
c_hi := c_hi + 1
The precedence of addition and subtraction is higher than the relational operators. Thus,
a + b > 20
is grouped as
(a + b) > 20
The more complicated expression
a + b > 20 && c - d <= e + f
is grouped as
((a + b) 20) && ((c - d) <= (e + f))
*, /, and %
)NOTE: Currently, none of these operators are implemented for generated code. It is permissible to use them in constant expressions though.
The multiplication operator is *, the division operator
is /, and the modulo operator is %. The
modulo operator returns the remainder of a division. These operators
are only defined for expressions of type `byte'. The order of execution
is strictly left to right. Thus,
a * b / c * d
is evaluated as:
((a * b) / c) * d
The precedence of multipliation and division is higher than addition and subtraction. Thus,
a * b + c / d
is grouped as
(a * b) + (c / d)
The more complicated expression
a * b + c > 20 && d / e - f < 30
is grouped as
(((a * b) + c) > 20) && (((d / e) - f) < 30)
|) The expression A | B computes the
bitwise OR of A and B. A and B must
both be the same type. This operation is defined for both type
bit and byte. Execution order is strictly left to
right.
NOTE: Currently, bitwise OR of type bit is not
implemented. Usually, you can make do with the conditional OR operator
(||).
The precedence of bitwise OR is higher than multiplication, division, addition, subtraction and all relational operators.
a | 1 + b | 2 * c | 3
is grouped as
(a | 1) + ((b | 2) * (c | 3))
The expression
a | 1 >= b | 2
is grouped as
(a | 1) >= (b | 2)
In C, this expression would group as
(a | (1 >= b)) | 2
which is pretty counter-intuitive.
&) The expression A & B computes the
bitwise AND of A and B. A and B
must both be the same type. This operation is defined for both type
bit and byte. Execution order is strictly left to
right.
NOTE: Currently, bitwise AND of type bit is not
implemented. Usually, you can make do with the conditional AND operator
(&&).
The precedence of bitwise AND is higher than bitwise OR, multiplication, division, addition, subtraction and all relational operators.
a & 1 | b & 2 | c & 4
is grouped as
((a & 1) | (b & 2)) | (c & 4)
The expression
a & 0xf = 0xb
is grouped as
(a & 0xf) = 0xb
In C, this expression would group as
a & (0xf >= b)
which is pretty counter-intuitive.
^) The expression A ^ B computes the
bitwise XOR (eXclusive OR) of A and B. A and
B must both be the same type. This operation is defined for both
type bit and byte. Execution order is
strictly left to right.
NOTE: Currently, bitwise XOR of type bit is not
implemented.
Bitwise XOR is used to toggle bits. If you want to complement the third bit in a register, try the following:
a := a ^ 4
The precedence of bitwise XOR is higher than bitwise AND, bitwise OR, multiplication, division, addition, subtraction and all relational operators. This means you can twiddle bits, mask them off, the then assemble them together without having to fight the operator precedence. For example,
a ^ 9 & 0xf | 0xa0
is grouped as
((a ^ 9) & 0xf) | 0xa0
and toggles the first and forth bits of a, masks off the four high order bits, and sets the fifth and seventh bits.
>>,
<<) The shift right operator is >> and the shift left
operator is <<. Order of operation is strictly left to
right. A << N causes A to be
shifted left by N bits with 0 being shifted into the least
significant bits. B >> N causes B
to be shifted right by N bits with 0 being shifted into the
most significant bits. Both the left and right operands the shift
operators must be of type byte. Thus, A <<
1 is equivalent to efficiently multiplying by 2 and
A << 2 is equivalent to multiplying by 4
. Similarly, B >> 1 is equivalent to dividing by 2
and B >> 2 is equivalent to dividing by 4.
NOTE: Currently, the code for shifting by a non-constant expression has not been implemented.
The precedence of the shift operators is greater than the bitwise operators. Thus,
a >> 4 | a << 4
is grouped as
(a >> 4) | (a << 4)
Incidently, this piece of code results in a value where the nibbles of a have been exchanged.
-,
!, ~)There are three unary operators:
-R- Minus R
~R- Bitwise NOT of R
!R- Logical NOT of R
The minus (-) and bitwise NOT (~byte. The
logical NOT operator (!) only works on a operand of type
bit
The precedence of the unary operators is higher than all the arithmetic and bit twiddling operators. Thus,
-a - b
is grouped as
(-a) - b
and
~a & b
is grouped as
(~a) & b
NOTE: Currently, there is a bug in the expression parser such
that a & ~b is not properly parsed.
NOTE: I've often thought that logical NOT (!)
should have a precedence between && and bit selection (
@). Thus, !A@N would group as !(A@N)
rather than (!A)@N. Similarly, I've often thought that
that unary minus should have a precedence right above multiplication (
*).
...[...]
)The array operator looks as follows:
Lwhere L is an expression that evaluates to either a string or a byte array, and R is an expression that evaluates to a byte. When the array operator occurs to the left of an assignment, a byte value is stored into the array; otherwise, a byte value is fetched.[R]
L.size)Currently, the dot operator has only one forms:
- L
.size- Fetch the size of L where L is an expression that evaluates to either a string or byte array.
P(...)) Procedure invocation is the act invoking a procedure using its
return value (or values) in an expression. P() invokes a
procedure P with no arguments, P(A1) inovkes
a preocedure with a single argument expression A1, and
P(A1, A2) invokes procedure P with argument
expressions A1 and A2.
The arguments to the procedure are evaluated in strict left to right order.
It is an error to invoke a procedure that does not return any return
value (i.e. returns_nothing) in an expression.
It is legal to invoke a procedure in an expression that returns
multiple values, provided the returned values are directly passed on as
arguments to another procedure invocation (or a multiple assignment.)
For example, assume that swap(a, b) returns b, a
. Further assume that p3 is a procedure that takes three
arguments. p3(swap(a, b), c) is legal and equivalent to
p3(b, a, c).
The precedence of procedure invocation is higher than all other operators.