Summary

If you have been following this series of articles about the FreeRTOS FAT SL filesystem, you might have read my post called “FreeRTOS FAT SL – Musings on my Implementation”.  In that post I asked myself “Why do I get the error message ‘undefined reference to xQueueCreateMutex'”.  Here is a screen shot from PSoC Creator

When I traced through the problem I noticed that it comes from this block of code:

#if F_FS_THREAD_AWARE == 1
	{
		extern SemaphoreHandle_t fs_lock_semaphore;

		if( fs_lock_semaphore == NULL )
		{
			fs_lock_semaphore = xSemaphoreCreateMutex();
            
			if( fs_lock_semaphore == NULL )
			{
				return F_ERR_OS;
			}
		}
	}
#endif /* F_FS_THREAD_AWARE */

Which gave me the hint that it had something to do with F_FS_THREAD_AWARE being turned on.  When I got the error message I assumed that it had something to do with the tangled mess of include files that I had created.  This flag is set in config_fat_sl.h

/**************************************************************************
**
**  FAT SL user settings
**
**************************************************************************/
#define F_SECTOR_SIZE           512  /* Disk sector size. */
#define F_FS_THREAD_AWARE       1     /* Set to one if the file system will be access from more than one task. */
#define F_MAXPATH               16    /* Maximum length a file name (including its full path) can be. */
#define F_MAX_LOCK_WAIT_TICKS   20

So, to “solve” the problem I just turned it off, knowing that I would need to come back to it to figure out because for sure if you are using the FreeRTOS FAT SL filesystem in an RTOS, which I am, you had better have the thread awareness turned on.  Specifically what the flag does is create and use a mutex around the actual “disk” to prevent re-entrant code from hosing you.

This morning I sat down and figured it out.  The answer is that I am an idiot.  Almost all of the features of FreeRTOS that you might want to use need to be turned on in the FreeRTOSConfig.h file.  This is true of mutex.  Here is the section of the file with the issue… look at line 19

#define configUSE_PREEMPTION                    1
#define configUSE_PORT_OPTIMISED_TASK_SELECTION 0
#define configUSE_TICKLESS_IDLE                 0
#define configCPU_CLOCK_HZ                      ( ( unsigned long ) CYDEV_BCLK__SYSCLK__HZ )
#define configTICK_RATE_HZ                      1000
#define configMAX_PRIORITIES                    5
#define configMINIMAL_STACK_SIZE                128
#define configMAX_TASK_NAME_LEN                 16
#define configUSE_16_BIT_TICKS                  0
#define configIDLE_SHOULD_YIELD                 1
#define configUSE_TASK_NOTIFICATIONS            1
#define configUSE_MUTEXES                       0 // <=== here is the problem line
#define configUSE_RECURSIVE_MUTEXES             0
#define configUSE_COUNTING_SEMAPHORES           0
#define configUSE_ALTERNATIVE_API               0 /* Deprecated! */
#define configQUEUE_REGISTRY_SIZE               10
#define configUSE_QUEUE_SETS                    0
#define configUSE_TIME_SLICING                  0
#define configUSE_NEWLIB_REENTRANT              0
#define configENABLE_BACKWARD_COMPATIBILITY     0
#define configNUM_THREAD_LOCAL_STORAGE_POINTERS 5

When I turn on the configUSE_MUTEXS things compile just fine and I can get on with my life.