In C, multicore function declaration question

twm47099 · 2013-12-29 11:01

In the tutorial C - Functions Multicore Example, the following is used to declare and define the function that is used in the new cog:

void adder(void *par);

I've looked through some of the c-libraries and see the same parameter when starting a function in a new cog. From reading my C text (void *par) is an untyped pointer to par. What does that do in relation to the function in the new cog? Is par a reserved variable name that is used any time a function is started in a different cog? In other words, if I am starting a different function in each of 3 cogs, would I use (void *par) as the parameter for each function?

Related question: Can I pass other parameters to a cog in a function call? If so what does the declaration of the function look like, and is void *par still one of the parameters?

Thanks again
Tom

jazzed · 2013-12-29 14:03

In "void adder(void *par);" the par is whatever you want it to be.

The name par is not special; it's just a declaration. It can be called "MarilynMonroll" if you like - a most interesting Sushi dish in Rocklin.

Some examples (code has not been test compiled):

int stack[200/4]; // 200 bytes of stack should be global.

volatile int parnum = 10; // par should be volatile to keep compiler from optimizing away code.
volatile int pararray[4];
typedef struct mystruct {
  volatile int request; volatile int response;
} MyST;

MyST *parstvar;

void adder1(void* num)
{
  int number = (int) num;
}

void adder2(void* numptr)
{
  int number = *(int*) numptr;
}

void adder3(void* array)
{
  int n;
  int *myArray = (int*) array;
  for(n = 0; n < 4; n++) {
    myArray[n] = n;
  }
}

void adder4(void* stptr)
{
  MyST sp = (MyST*) stptr;
}

int main(void) {
  cogstart(adder, (void*) parnum, &stack, sizeof(stack)); // passes the value in parnum to the function - not recommended.
  cogstart(adder, &parnum, &stack, sizeof(stack)); // passes the address of parnum to the function.
  cogstart(adder, &pararray[0], &stack, sizeof(stack)); // passes the address of pararray[0] to the function. 
  cogstart(adder, &parstvar, &stack, sizeof(stack)); // passes the address of pararray[0] to the function.
  return 0;
}

Reference: https://sites.google.com/site/propellergcc/documentation/libraries/propeller-h-library#TOC-cogstart

Tymkrs · 2014-01-02 17:13

I believe we go into each line of the code and explain what it is and what can be done with each line if you're interested twm:

http://www.tymkrs.com/shows/episode/firstc-episode-011/

In C, multicore function declaration question

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