Re: Semaphore support

Altera_Forum · ‎08-22-2005

Hi,

I'm currently trying to initialize a semaphore by making a call to sem_init(), but instead of returning a non-zero value and printing a error condition, Nios II reboots.

struct sem_t *msem
if (sem_init(msem, 0, 0) != 0)
   printf("Semaphore not initialized\n");

Is there something specific that needs to be configured in the kernel that provides support for semaphores?

Any feedback would be appreciated.

Altera_Forum · ‎08-23-2005

Hi bjskill,

The sem_init() routine initializes the semaphore object that the first argument points to. So you're passing

in an un-initialized pointer ... and something ends up getting trashed. Try:

/*struct sem_t *msem */

struct sem_t msem

/*if (sem_init(msem, 0, 0) != 0)*/

if (sem_init (&msem, 0, 0) != 0)

printf("Semaphore not initialized\n");

Regards,

--Scott

Altera_Forum · ‎08-23-2005

Hi smcnutt,

I made some errors when I made my original post. When SemInit() is called something seems to get trashed and cause Nios to reboot:

SemInit(myThreadName, &mySem, "mySemaphore");

void SemInit(char *who, sem_t *mSem, char *label)
{
   printf("%s is initializing %s\n", who, label);  // Debug message
   if (sem_init(mSem, 0, 0) != 0)
      printf("Failed when initializing semaphore.\n");  // Error message
   printf("%s has initialized %s\n", who, label);  // Debug message
   return;
}

I don't see either the debug or error messages displayed before the reboot.

Thanks for your help.

Altera_Forum · ‎08-23-2005

I'm not sure if this is the problem, but you may need to turn on IPC support in the kernel in order for semaphore support to work.

Take a look at:

.../altera/kits/nios2/examples/software/linux/apps/samples/thread

for an example of semaphores...

Altera_Forum · ‎08-23-2005

Hi Ken,

I think that might be the problem. However, I only get an "undefined reference to 'sem_init'" error from the linker when DEBUG=1 and it attempts to generate the .gdb file. When DEBUG=0, the linker does not report any errors or warnings when it generates the application.

What path do I need to follow within the kernel configuration menu to check and see if IPC support is turned on? The only choice in the menu options that I found that was related to semaphores is "General Setup --> POSIX message queues". Is that right?

I'll also take a look at those linux examples to make sure I'm initializing the semaphores correctly.

Thanks for your help.

UPDATE: (8/24/05):

I enabled the "General Setup -> POSIX message queues" from the kernel configuration menu, performed a new build, and downloaded the new vmlinux.bin file. However, the application still causes a Nios2 reboot as soon as sem_init() is called. Is there something else I'm missing?

Altera_Forum · ‎08-29-2005

Sorry for the late reply, how about you post your full code and I'll run it on my board to see what happens?