Getting ITM to work on Cortex-M3 (STM32) using SWV

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  • Getting ITM to work on Cortex-M3 (STM32) using SWV

    Hello!

    I'm trying to get the ITM 'printf' functionality working on a Cortex-M3 (STM32F103ZE, running at 72Mhz) with a J-Link Ultra, using SWV mode.
    The following code is used to enable the ITM output via TPUI:

    C Source Code

    1. const char mystring[] = "Hello world";
    2. char* s;
    3. CoreDebug->DEMCR = CoreDebug_DEMCR_TRCENA_Msk;
    5. *((uint32_t*)0xE0040010) = 12; //Async Clock Prescaler Register
    6. *((uint32_t*)0xE0040304) = 0; //Formatter and Flush Control Register
    7. *((uint32_t*)0xE00400F0) = 1; // Selected Pin Protocol Register
    8. DBGMCU->CR = 0x00000020; // Set asynchronuous communication via DBGMCU_CR
    9. ITM->LAR = 0xC5ACCE55;
    10. ITM->TCR |= ITM_TCR_ITMENA_Msk | ITM_TCR_SYNCENA_Msk | (1UL << ITM_TCR_ATBID_Pos);
    11. ITM->TER |= 1UL;
    12. ITM->TPR |= 1UL;
    Display All

    I'n not sure about the following settings:
    • Prescale register (72Mhz/12 = 6Mhz, the same as the J-Link, right?)
    • Formatter and flush control register
    • Protocol register (1 == manchester encoded, 2 == NRZ)
    • Maybe some more settings ;(
    Then, in J-Link commander, I use swostart followed by sworead to display the captured data:
    J-Link>sworead
    1 bytes read (1 bytes in host buffer)
    00000000 = 00
    After trying several settings, the above code at least returns some data, although its not what I expect...

    Can anybody help in getting this to work, and is there some way to display the captured SWO data as ASCII, instead of HEX-dump?

    Thanks!

  • Hi,

    below some sample code which has been used with J-Link for some SWO testing on an IAR STM32F103ZE-SK:

    C Source Code

    1. #define ITM_PORT *(volatile unsigned *)0xE0000000
    3. /*********************************************************************
    4. *
    5. * _Delay
    6. */
    7. static void _Delay(int NumLoops) {
    8. volatile int i;
    10. for (i = 0; i < NumLoops; i++);
    11. }
    13. /*********************************************************************
    14. *
    15. * main
    16. */
    17. int main(void) {
    18. int i;
    19. U32 SWOPrescaler;
    20. U32 SWOSpeed;
    22. <Init PLL, set CPU clock to 72 MHz> // Optional, so I do not pos it here
    24. SWOSpeed = 6000000;
    25. *((volatile unsigned *)0xE000EDFC) = 0x01000000; // "Debug Exception and Monitor Control Register (DEMCR)"
    26. *((volatile unsigned *)0xE0042004) = 0x00000027;
    27. *((volatile unsigned *)0xE00400F0) = 0x00000002; // "Selected PIN Protocol Register": Select which protocol to use for trace output (2: SWO)
    28. SWOPrescaler = (72000000 / SWOSpeed) - 1; // SWOSpeed in Hz
    29. *((volatile unsigned *)0xE0040010) = SWOPrescaler; // "Async Clock Prescaler Register". Scale the baud rate of the asynchronous output
    30. *((volatile unsigned *)0xE0000FB0) = 0xC5ACCE55; // ITM Lock Access Register, C5ACCE55 enables more write access to Control Register 0xE00 :: 0xFFC
    31. *((volatile unsigned *)0xE0000E80) = 0x0001000D; // ITM Trace Control Register
    32. *((volatile unsigned *)0xE0000E40) = 0x0000000F; // ITM Trace Privilege Register
    33. *((volatile unsigned *)0xE0000E00) = 0x00000001; // ITM Trace Enable Register. Enabled tracing on stimulus ports. One bit per stimulus port.
    34. *((volatile unsigned *)0xE0001000) = 0x400003FE; // DWT_CTRL
    35. *((volatile unsigned *)0xE0040304) = 0x00000100; // Formatter and Flush Control Register
    37. i = 0;
    38. while (1) {
    39. _Delay(100);
    40. while (ITM_PORT == 0); // Wait while Fifo full
    41. ITM_PORT = i; // Output counter
    42. i++;
    43. }
    Display All


    Hope it helps.


    Best regards
    Alex
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  • Hi Alex,

    Many thanks for your clear example.
    I ran the code exactly on my STM32, but no output is produced at all...
    Do I have to configure anything in J-Link commander before retrieving the output or could something else be wrong?

    Thanks!