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global variable corruption on at90can128Posted by sebamz on November 12, 2013 Hi, I'm having a problem with a global variable I use in my main.c. I use CANFIFO as a buffer to store measured data. When I start the debugger and the program counter is at the beginning of main, there are already values different from zero in CANFIFO. The amount of values already written in CANFIFO seems to be dependent on how many tasks I create. E.g. if I create only one task, about four values in CANFIFO are written and the rest can be used as intended for buffering data. If I create more tasks, there are only a few elements left in which data is stored in the course of the program. I'm not sure whether my problem is only a compiler issue or about FreeRTOS. Could someone please give me a few ideas on what could be the cause of this effect? Please pardon the german comments in my code. Best regards. compiler: avrgcc 4.5.1 (AVR Studio 4.19) debugger: Olimex AVR-JTAG-USB main.c <!-- HTML generated using hilite.me --> /* FreeRTOS V7.5.2 - Copyright (C) 2013 Real Time Engineers Ltd. global variable corruption on at90can128Posted by richardbarry on November 12, 2013 If this happens before you have started the scheduler then I doubt it is an RTOS problem, and is most likely a simple linker script problem. When you create a task FreeRTOS will call pvPortMalloc() to allocate some RAM. Where that RAM comes from is dependent on which memory allocator you have included in your project. http://www.freertos.org/a00111.html Are you using heap1.c, heap2.c or heap_4.c? If so then the RAM will come from a statically allocated array, and if writing to that array is also writing into your CAN buffer then there is a problem with the memory map/linker script. You can configure a malloc() failed hook function with these to trap running out of memory in the static array. If instead you are using heap_3.c then the memory will come from the heap as allocated by GCC when the standard GCC malloc() is called. In this case your build files must allocate a heap that is large enough. Often with GCC an overflowed heap is not detectable. Your code does not show what a struct Buffer type is. Are you sure it is itself actually allocating a buffer and not just a pointer to a buffer that you should be allocating yourself? Regards. global variable corruption on at90can128Posted by sebamz on November 12, 2013 Hi Richard, thank you for the fast response. I'm using heap_2.c and in my settings heap size for tasks should be way enough for about ten tasks. <!-- HTML generated using hilite.me --> #define configMINIMALSTACKSIZE ( ( unsigned short ) 85 ) #define configTOTALHEAPSIZE ( (size_t ) ( 3500 ) ) this is struct Buffer defined in buffer.h <!-- HTML generated using hilite.me --> struct Buffer { uint16t data[BUFFERSIZE]; uint8t read; uint8t write; }; You're right, I'm not sure if I'm introducing CANFIFO the right way (in this case I don't really know what I'm doing, which is bad...). I'll try to force the compiler to allocate memory for CANFIFO before allocating memory for other purposes. Best regards.
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