DS80C400 reentrant multi tasking function calls with Keil compiler

Hi there,

I'm looking for some tips on how to correctly use C functions marked as 
reentrant under a Keil development environment (C51 V7.08) on a Dallas 
DS80C400.   I believe the startup400.a51 file is configured correctly 
with USE_REENTRANT_STACK=1.  I have included example source at end of 
the email.

Specifically I'm trying to call a reentrant function from multiple tasks 
and an unable to do so without corrupting local function variables - 
perhaps what I'm trying to do is inappropriate, but I'd like to know if 
its possible and what I'm doing wrong.

I have successfully managed to demonstrate that recursive, reentrant 
calls to an example reentrant function behave correctly, thus calls to 
oozlum_bird() from a single task work as expected. ie output

-> oozlum_bird() PID:01 localfncvar: 0 anumber: 0
-> oozlum_bird() PID:01 localfncvar: 1 anumber: 1
-> oozlum_bird() PID:01 localfncvar: 2 anumber: 2
-> oozlum_bird() PID:01 localfncvar: 3 anumber: 3
<- oozlum_bird() PID:01 localfncvar: 3 anumber: 4
<- oozlum_bird() PID:01 localfncvar: 2 anumber: 3
<- oozlum_bird() PID:01 localfncvar: 1 anumber: 2
<- oozlum_bird() PID:01 localfncvar: 0 anumber: 1

This shows a local function variable being set  to anumber.   anumber is 
incremented and passed as the input parameter to oozlum_bird().  
oozlum_bird() returns after a number of recursive calls.  anumber is one 
greater than it was initially as expected.

Calls to a non-reentrant version of the function give the expected 
results of localfncvar being affected.

-> non_oozlum_bird() PID:01 localfncvar: 0 anumber: 0
-> non_oozlum_bird() PID:01 localfncvar: 1 anumber: 1
-> non_oozlum_bird() PID:01 localfncvar: 2 anumber: 2
-> non_oozlum_bird() PID:01 localfncvar: 3 anumber: 3
<- non_oozlum_bird() PID:01 localfncvar: 3 anumber: 4
<- non_oozlum_bird() PID:01 localfncvar: 3 anumber: 4
<- non_oozlum_bird() PID:01 localfncvar: 3 anumber: 4
<- non_oozlum_bird() PID:01 localfncvar: 3 anumber: 4

However, when I create two tasks to call the same function,  localfncvar 
is affected between tasks as can be seen by the following output fragment:

-> oozlum_bird() PID:29 localfncvar: 1 anumber: 1
-> oozlum_bird() PID:53 localfncvar: 2 anumber: 2
-> oozlum_bird() PID:29 localfncvar: 3 anumber: 3
-> oozlum_bird() PID:53 localfncvar: 4 anumber: 4
<- oozlum_bird() PID:29 localfncvar: 4 anumber: 5
<- oozlum_bird() PID:53 localfncvar: 2 anumber: 3
<- oozlum_bird() PID:29 localfncvar: 1 anumber: 2
<- oozlum_bird() PID:53 localfncvar: 0 anumber: 1
<- oozlum_bird() PID:53 localfncvar: 0 anumber: 0


Any pointers to where I'm going wrong would be greatly appreciated.

Richard

Example code follows.


#include <stdio.h>             #include <string.h>            #include 
"rom400_init.h"
#include "rom400_task.h"

//
// Some defines for the program run.
//
#define RAM_START             0x14000
#define RAM_END               0x6F000



void oozlum_bird(int anumber) reentrant;

#define CALL_DEPTH_LIMIT 4



/*
* This function should preserve automatic variables as it burrows down 
into itself
*/
void oozlum_bird(int anumber) reentrant
{
 // I want this var to be unaffected by calls to function for different 
tasks
 volatile unsigned localfncvar = 0;

 task_wait(0, 0, 2000);

 task_entercritsection();
   localfncvar = anumber;
   printf("-> oozlum_bird() PID:%b02x localfncvar: %d anumber: %d \r\n", 
task_getcurrent(), localfncvar, anumber++);
 
 task_leavecritsection();

 // recursively call oozlum_bird() upto a call depth limit
 if (CALL_DEPTH_LIMIT > anumber)
 {
   oozlum_bird(anumber);
 }

 task_wait(0, 0, 2000);

 task_entercritsection();
   printf("<- oozlum_bird() PID:%b02x localfncvar: %d anumber: %d \r\n", 
task_getcurrent(), localfncvar, anumber);
 task_leavecritsection();
}

/*
* Non reentrant version of oozlum_bird()
*/
void non_oozlum_bird(int anumber)
{

 volatile unsigned localfncvar = 0;

 task_wait(0, 0, 2000);

 task_entercritsection();
   localfncvar = anumber;
   printf("-> non_oozlum_bird() PID:%b02x localfncvar: %d anumber: %d 
\r\n", task_getcurrent(), localfncvar, anumber++);
 
 task_leavecritsection();

 // recursively call oozlum_bird() upto a call depth limit
 if (CALL_DEPTH_LIMIT > anumber)
 {
   non_oozlum_bird(anumber);
 }

 task_wait(0, 0, 2000);

 task_entercritsection();
   printf("<- non_oozlum_bird() PID:%b02x localfncvar: %d anumber: %d 
\r\n", task_getcurrent(), localfncvar, anumber);
 task_leavecritsection();
}


/*
* Spawn of process that repeatedly calls oozlum_bird()
*/
void spawn_test() reentrant
{
   unsigned int result;


   task_entercritsection();   // make sure we don't task swap before we 
can get the result out
   result = task_fork(NORM_PRIORITY, ROM_SAVESIZE);

   if (result==0xFFFF)
   {
       task_leavecritsection();
       printf("Attempt to fork failed\r\n");
       return;
   }
   //else result is 0 for the child process, else it is the child PID

   if (result==0)
   {
       // This is the stuff that happens in the task just generated by 
the fork call

     while(1)
     {
         oozlum_bird(0);
         task_wait(0, 0, 2000);
     }
   }
   else
   {
     // This is the parent task
     task_leavecritsection();
 
   }
}



void main(void)
{
   unsigned char ch;
 
   printf("\r\n Reentrant call investigation\r\n\r\n");

   printf("DS80C400 Initialization Library Version %d\r\n", 
init_version());
   printf("DS80C400 Scheduler Library Version      %d\r\n", 
task_version());

   printf("About to perform an init of the rom...\r\n\r\n");
   init_rom(RAM_START, RAM_END);

   task_settickreload(RELOAD_14_746);



   while (1)
   {
       //let's implement a menu system for this thing...
       printf("\r\n*********************************************\r\n");
       printf("       Reentrant call investigation             *\r\n");
       printf("                                                *\r\n");
       printf(" s - SPAWN an oozlum_bird process               *\r\n");
       printf(" o - Make call to oozlum_bird (recursive)       *\r\n");
       printf(" n - Make call to non_oozlum_bird               *\r\n");

       printf("Enter your choice: ");
       ch = getchar();
       printf("\r\n");
                     switch(ch)
       {


           case 's' : spawn_test();
                      break;

           case 'o' : oozlum_bird(0);
                       break;
           case 'n' : non_oozlum_bird(0);
                       break;
           default  : printf("Huh???\r\n");
       }
   }

   printf("\r\nThe program will now freeze.");

   while(1)
   {
   };
}








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