Language Syntax#

simpPRU is a procedural programming language.
It is a statically typed language. Variables and functions must be assigned data types during compilation.
It is type-safe, and data types of variables are decided during compilation.
simPRU codes have a .sim extension.

Datatypes#

int - Integer datatype
bool - Boolean datatype
char / uint8 - Character / Unsigned 8 bit integer datatype
void - Void datatype, can only be used a return type for functions

Constants#

<any_integer> - Integer constant. Integers can be decimal, hexadecimal (start with 0x or 0X) or octal (start with 0)
'<any character>' - Character constant. These can be assigned to both int and char/uint8 variables
true - Boolean constant (True)
false - Boolean constant (False)
Px_yz - Pin mapping constants are Integer constant, where x is 1,2 or 8,9 and yz are the header pin numbers.

Operators#

{,} - Braces
(,) - Parenthesis
/,*,+,-,% - Arithmetic operators
>,<,==,!=,>=,<= - Comparison operators
~,&,|,<<,>> - Bitwise operators: not, and, or and bitshifts
not,and,or - Logical operators: not, and, or
:= - Assignment operator
Result of Arithmetic and Bitwise operators is Integer constant.
Result of Comparison and Logical operators is Boolean constant.
Characters are treated as integers when used in Arithmetic expressions.
Only Integer constants can be used with Arithmetic and Bitwise operators.
Only Integer constants can be used with Comparison operators.
Only Boolean constants can be used with Logical operators.
Operators are evaluated following these precedence rules.

Correct: bool out := 5 > 6;
Wrong:   int yy := 5 > 6;

Variable declaration#

Datatype of variable needs to be specified during compile time.
Variables can be assigned values after declarations.
If variable is not assigned a value after declaration, it is set to 0 for integer and char/uint8 and to false for boolean by default.
Variables can be assigned other variables of same datatype. ints and chars can be assigned to each other.
Variables can be assigned expressions whose output is of same datatype.

Declaration#

int var;
char char_var;
bool test_var;

Assignment during Declaration#

int var := 99;
char char_var := 'a';
uint8 short_var := 255;
bool test_var := false;

Assignment#

var := 45;
short_var := var;
test_var := true;

Variables to be assigned must be declared earlier.
Datatype of the variables cannot change. Only appropriate expressions/constants of their respective datatypes can be assigned to the variables.
Integer and Character variable can be assigned only Integer expression/Integer constant/Character constant.
Boolean variable can be assigned only Boolean expression/constant.

Arrays#

Arrays are static - their size has to be known at compile time and this size cannot be changed later.
Arrays can be used with bool, int and char.
Arrays do not support any arithmetic / logical / comparison / bitwise operators, however these operators work fine on their elements.

Declaration and Assignment#

The data type has to be specified as data_type[size].
Array of char can be initialized from a double quoted string, where the length of the array would be at least the length of the string plus 1.

int[16] a; /* array of 16 integers */
char[20] string1 := "I love BeagleBoards";

Indexing:#

Arrays are zero-indexed.
The index can be either a char or an int or an expression involving chars and ints.
Accessing elements of an array:

int a := arr[4]; /* Copy the 5th element of arr to a */

Changing elements of an array:

arr[4] := 5; /* The 5th element of arr is now 5 */

int i := 4;
arr[i] := 6; /* The 5th element of arr is now 6 */

char j := 4;
arr[j] := 7; /* The 5th element of arr is now 7 */

arr[i+j] := 1; /* The 9th element of arr is now 1 */

/* Declaring and initializing an array with all zeros */
int[16] arr;
for: i in 0:16 {
    arr[i] := 0;
}

Comments#

simpPRU supports C style multiline comments.

/* This is a comment */

/* Comments can span
multiple lines */

Keyword and Identifiers#

Table 132 Reserved keywords#
``true``	``read_counter``	``stop_counter``
``false``	``start_counter``	``pwm``
``int``	``delay``	``digital_write``
``bool``	``digital_read``	``def``
``void``	``return``	``or``
``if``	``and``	``not``
``elif``	``continue``	``break``
``else``	``while``	``in``
``for``	``init_message_channel``	``send_message``
``receive_message``	``print``	``println``

Valid identifier naming#

An identifier/variable name must be start with an alphabet or underscore (_) only, no other special characters, digits are allowed as first character of the identifier/variable name.

product_name, age, _gender
Any space cannot be used between two words of an identifier/variable; you can use underscore (_) instead of space.

product_name, my_age, gross_salary
An identifier/variable may contain only characters, digits and underscores only. No other special characters are allowed, and we cannot use digit as first character of an identifier/variable name (as written in the first point).

length1, length2, _City_1

Detailed info: https://www.includehelp.com/c/identifier-variable-naming-conventions.aspx

Expressions#

Arithmetic expressions#

=> (9 + 8) * 2 + -1;
33
=> 11 % 3;
2
=> 2 * 6 << 2 + 1;
96
=> ~0xFFFFFFFF;
0

Boolean expressions#

=> 9 > 2 or 8 != 2 and not( 2 >= 5 or 9 <= 5 ) or 9 != 7;
true
=> 0xFFFFFFFF != 0XFFFFFFFF;
false
=> 'a' < 'b';
true

Note : Expressions are evaluated following the operator precedence <#operators>

If-else statement#

Statements in the if-block are executed only if the if-expression evaluates to true. If the value of expression is true, statement1 and any other statements in the block are executed and the else-block, if present, is skipped. If the value of expression is false, then the if-block is skipped and the else-block, if present, is executed. If elif-block are present, they are evaluated, if they become true, the statement is executed, otherwise, it goes on to eval next set of statements

Syntax#

if : boolean_expression {
    statement 1
    ...
    ...
}
elif : boolean_expression {
    statement 2
    ...
    ...
    ...
}
else {
    statement 3
    ...
    ...
}

Examples#

int a := 3;

if : a != 4 {
    a := 4;
}
elif : a > 4 {
    a := 10;
}
else {
    a := 0;
}

This will evaluate as follows, since a = 3, if-block (3!=4) will evaluate to true, and value of a will be set to 4, and program execution will stop.

For-loop statement#

For loop is a range based for loop. Range variable is a local variable with scope only inside the for loop.

Syntax#

for : var in start:stop {
    statement 1
    ....
    ....
}

Here, for loop is a range based loop, value of integer variable var will vary from start to stop - 1. Value of var does not equal stop. Here, increment is assumed to be 1, so start will have to less than stop.
Optionally, start can be skipped, and it will automatically start from 0, like this:

for : var in :stop {
    statement 1
    ....
    ....
}

Optionally, increment can also be specified like this. Here, stop can be less than start if increment is negative.

for : var in start:stop:increment {
    statement 1
    ....
    ....
}

Note : var is a integer, and start, stop, increment can be arithmetic expression, integer or character variable, or integer or character constant.

Examples#

int sum := 0;

for : i in 1:4 {
    sum = sum + i;
}

int mx := 32;
int nt;

for : j in 2:mx-10 {
    nt := nt + j;
}

int sum := 0;

for : i in in 10:1:-2 { /*10, 8, 6, 4, 2*/
    sum = sum + i;
}

While-loop statement#

While loop statement repeatedly executes a target statement as long as a given condition is true.

Syntax#

while : boolean_expression {
    statement 1
    ...
    ...
}

Examples#

Infinite loop

while true {
    do_something..
    ...
}

Normal loop, will repeat 30 times, before exiting

int tag := 0;

while : tag < 30 {
    tag := tag + 1;
}

Control statements#

Note : break and continue can only be used inside looping statements

break#

break is used to break execution in a loop statement, either for loop or while loop. It exits the loop upon calling.

Syntax#

break;

Examples#

for : i in 0:9 {
    if : i == 3 {
        break;
    }
}

continue#

continue is used to continue execution in a loop statement, either for loop or while loop.

Syntax#

continue;

Examples#

for : j in 9:19 {
    if : i == 12 {
        continue;
    }
    else {
        break;
    }
}

Functions#

Function definition#

A function is a group of statements that together perform a task. You can divide up your code into separate functions. How you divide up your code among different functions is up to you, but logically the division usually is such that each function performs a specific task. A function declaration tells the compiler about a function’s name, return type, and parameters. A function definition provides the actual body of the function.

Warning : Function must be defined before calling it.

Syntax#

def <function_name> : <data_type> : <data_type> <param_name>, <data_type> <param_name>, ... {
    statement 1;
    ...
    ...

    return <data_type>;
}

Note

If return data type is void, then return statement is not needed, and if still it is added, it must be return nothing, i.e., something like this return ;

Warning

return can only be present in the body of the function only once, that too at the end of the function, not inside any compound statements.

Danger

return inside a compound statement, this syntax is not allowed.

def test : int : int a {
if : a < 4 {
return a;
}
}

Correct : return is not inside compound statements, It should be placed only at the end of function definition

def test : int : int a {
int gf := 8;
if : a < 4
{
gf := 4;
}
return gf;
}

Examples#

Examples according to return types

Integer

def test_func : int : int a, int b
{
   int aa := a + 5;
   if : aa < 3 {
        aa : = 0;
   }

   return aa + b;
}

Character

def next_char : char : char ch, int inc {
   char chinc := ch + inc;
   return chinc;
}

Boolean

def compare : bool : int val {
   bool ret :=false;
      if : val < 0 {
         ret := true;
      }
      return ret;
   }

Void

def example_func_v : void : {
    int temp := 90;

    return;
}

Function call#

Functions can be called only if, they have been defined earlier. They return data types according to their definition. Parameters are passed by value. Only pass by value is supported as of now.

Syntax#

function_name(var1, var2, ..);

Examples#

Integer int a := 55; int ret_val := test_func(4, a);
Character char a := 'a'; char b := next_char(a, 1);
Boolean bool val := compare(22); compare(-2);
Void example_func(false); example_func_v();

Testing or Debugging#

For testing or debugging code, use the –test or -t flag to enable print, println and stub functions. Use –preprocess to stop after generating the C code only. Then run the generated C code (at /tmp/temp.c) using gcc.

Print functions#

print can take either a string (double quoted) or any int / char / bool identifier.

println is similar to print but also prints a newline (\n).

Examples

print("Hello World!");
int a := 2;
print(a);
a := a + 2;
print(a);
println("");

Stub functions#

PRU specific functions will be replaced by stub functions which print function_name called with arguments arg_name when called.