# vTaskSwitchContext not working on PIC32 **URL:** \ **Category:** Kernel\ **Created:** [September 16, 2008, 10:30pm UTC](https://forums.freertos.org/t/vtaskswitchcontext-not-working-on-pic32/5253 "2008-09-16T22:30:53Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [September 16, 2008, 10:30pm UTC](https://forums.freertos.org/t/vtaskswitchcontext-not-working-on-pic32/5253/1 "2008-09-16T22:30:53Z")
**[kg4ysn](https://sourceforge.net/u/kg4ysn/)** wrote on [Tuesday, September 16, 2008](https://sourceforge.net/p/freertos/discussion/382005/thread/e77a02e4/#fc69): Hey all, I posted a message the other day regarding problems with the PIC32 and the MPLAB SIM environment.  As I poked around some more, it turns out that the problem may be more involved. Within a single time slice, prvIdleTask performs as expected – the PC works down through the function to vApplicationIdleHook and then loops.  I was able to confirm this by toggling some GPIO pins and watching them with an oscilloscope. During the evaluation of line 1699 in tasks.c, a “sltiu v0,v0,2” instruction is issued.  The next command should be “bne v0,zero,0x9d0014f4.”  However, the PC instead jumps to 9FC0\_1200, which is the location for portSAVE\_CONTEXT from ISR\_Support.h.  So I’m guessing that some kind of timer triggered off an asynchronous event, and we’re now entering vTaskSwitchContext. vTaskSwitchContext processes through, and as portRESTORE\_CONTEXT is called, we end with our "ERET" instruction at 9D00\_4B78.  But instead of jumping back to where we were at 9D00\_14F4, we jump right back to portSAVE\_CONTEXT and begin the process anew.  This continues ad infinium, causing the simulator to crash (due to a spurious error related to "sd ra,-1(ra)" being processed as NOP) and the real PIC32 board to hang. The full contents of FreeRTOSConfig.h are below.  Anyone have an idea on how to solve this one?  Is this a bug in v5.0.3, or is it a user error? Thanks, Chris #define configUSE\_PREEMPTION            1 #define configUSE\_IDLE\_HOOK                1 #define configUSE\_TICK\_HOOK                0 #define configTICK\_RATE\_HZ                ( ( portTickType ) 1000 ) #define configCPU\_CLOCK\_HZ                ( ( unsigned portLONG ) 80000000UL )  #define configPERIPHERAL\_CLOCK\_HZ        ( ( unsigned portLONG ) 40000000UL ) #define configMAX\_PRIORITIES            ( ( unsigned portBASE\_TYPE ) 5 ) #define configMINIMAL\_STACK\_SIZE        ( 400 ) #define configISR\_STACK\_SIZE            ( 500 ) #define configTOTAL\_HEAP\_SIZE            ( ( size\_t ) 28000 ) #define configMAX\_TASK\_NAME\_LEN            ( 8 ) #define configUSE\_TRACE\_FACILITY        0 #define configUSE\_16\_BIT\_TICKS            0 #define configIDLE\_SHOULD\_YIELD            1 #define configUSE\_MUTEXES                1 #define configCHECK\_FOR\_STACK\_OVERFLOW    2 #define configQUEUE\_REGISTRY\_SIZE        0 #define configUSE\_CO\_ROUTINES             0 #define configMAX\_CO\_ROUTINE\_PRIORITIES ( 2 ) #define INCLUDE\_vTaskPrioritySet        1 #define INCLUDE\_uxTaskPriorityGet        1 #define INCLUDE\_vTaskDelete                0 #define INCLUDE\_vTaskCleanUpResources    0 #define INCLUDE\_vTaskSuspend            1 #define INCLUDE\_vTaskDelayUntil            1 #define INCLUDE\_vTaskDelay                1 #define INCLUDE\_uxTaskGetStackHighWaterMark    1 #define configKERNEL\_INTERRUPT\_PRIORITY        0x01 #define configMAX\_SYSCALL\_INTERRUPT\_PRIORITY    0x03 ---
**Author:** ![rtel](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rtel/32/31_2.png) [@rtel](https://forums.freertos.org/u/rtel)\ **Post date:** [September 17, 2008, 6:42am UTC](https://forums.freertos.org/t/vtaskswitchcontext-not-working-on-pic32/5253/2 "2008-09-17T06:42:40Z")
**[rtel](https://sourceforge.net/u/rtel/)** wrote on [Wednesday, September 17, 2008](https://sourceforge.net/p/freertos/discussion/382005/thread/e77a02e4/#fc69/40f3): Exiting one interrupt then entering another is not necessarily an error - this could be a legitimate execution patter especially if interrupts are nesting. It is my understanding the the simulator is a bit ‘limited’ when it comes to PIC32.  I’m sure it will be improved. Which hardware are you using/do you have access to an Explorer 16?  Ideally can you confirm that you have the demo as provided in the [FreeRTOS.org](http://FreeRTOS.org) download running before making any modifications? If you have different hardware, then can you try a simple LED flashing example first - see [http://www.freertos.org/porting-a-freertos-demo-to-different-hardware.html](http://www.freertos.org/porting-a-freertos-demo-to-different-hardware.html) . The PIC32 port is being used on some quite complex projects so I am as confident as I can be that it is sound, but obviously I cannot guarantee it.  I too have used it quite extensively. Have you checked that you are not overflowing your stacks? Regards. ---
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [September 17, 2008, 3:41pm UTC](https://forums.freertos.org/t/vtaskswitchcontext-not-working-on-pic32/5253/3 "2008-09-17T15:41:43Z")
**[kg4ysn](https://sourceforge.net/u/kg4ysn/)** wrote on [Wednesday, September 17, 2008](https://sourceforge.net/p/freertos/discussion/382005/thread/e77a02e4/#fc69/e3d3): Hi Richard, Thanks for the posting.  There definitely wasn’t any overflowing of stacks; I used an LED-style example to do debugging to determine if this was the case. After comparing against the demo code, I found that I had missed a tiny #pragma config declaration.  Once I corrected that, the timers seemed to fire off correctly, and context switching worked as expected.  So chalk this one up to user error.  🙂 Thanks for taking the time to look into it! Chris