ITM usage and SWO pin

[Davide Michelis]

Posted on June 06, 2018 at 10:25

Good morning,

I am trying to add some trace capabilities to my system: UART is obviously too slow so I would like to use ITM. I report my situation:

I use a STM32F3DISCO board, FreeRTOS, Eclipse with Jlink debugger plugin and AC6 plugin as IDE and JLink when I need it (I don't have a physical JLink probe but I reflash the micro).

I have implemented the code but nothing works: probably I didn't understand everything. The code I use is:

&sharpdefine DEMCRx   (*((unsigned long *) 0xe000edfc))&sharpdefine TRCENA  0x01000000  // enable trace&sharpdefine ITM_STIM0 (*((unsigned long *) 0xe0000000))&sharpdefine ITM_STIM1 (*((unsigned long *) 0xe0000004))&sharpdefine ITM_STIM2 (*((unsigned long *) 0xe0000008))&sharpdefine ITM_STIM3 (*((unsigned long *) 0xe000000c))&sharpdefine ITM_TER   (*((unsigned long *) 0xe0000e00))&sharpdefine ITM_TPR   (*((unsigned long *) 0xe0000e40))&sharpdefine ITM_TCR   (*((unsigned long *) 0xe0000e80))&sharpdefine ITM_LAR   (*((unsigned long *) 0xe0000fb0))&sharpdefine ITM_LAR_ACCESS  0xc5acce55&sharpdefine DBGMCU              ((DBGMCU_TypeDef *) DBGMCU_BASE)

void itm_init(void) {

    uint32_t SWOSpeed = 3000000;    uint32_t SWOPrescaler = (48000000 / SWOSpeed) - 1; // SWOSpeed in Hz

    CoreDebug->DEMCR = 1 << CoreDebug_DEMCR_TRCENA_Pos;

    DBGMCU->CR = 0x00000027;

    *((volatile unsigned *) 0xE00400F0) = 0x00000002;    *((volatile unsigned *) 0xE0040010) = SWOPrescaler;     *((volatile unsigned *) 0xE0000FB0) = 0xC5ACCE55;    *((volatile unsigned *) 0xE0000E80) = 0x0001000D;     *((volatile unsigned *) 0xE0000E40) = 0x0000000F;    *((volatile unsigned *) 0xE0000E00) = 0x00000001;    *((volatile unsigned *) 0xE0001000) = 0x400003FE;     *((volatile unsigned *) 0xE0040304) = 0x00000100;}

int SWO_PrintChar(int ch){

    (void) ITM_SendChar(ch);

    return(ch);

}

void SWO_PrintString(const char *s) {

  while (*s!='\0') {    SWO_PrintChar(*s++);  }}

ITM_SendChar() is already defined in core_cm4.c

I have connected PB3 to pin6 of CN3 because SB10 is not soldered...which utility may I use to see the output of my SWO_PrintString calls?

Thank you in advance.

Best regards

#itm #swd #jlink #freertos #debug #trace #swo

[Davide Michelis]

Posted on June 06, 2018 at 10:48

I have tried in this way just now: I reflashed the firmware stlink->jlink, then using the Jlink SWO viewer i have tried to get data, but nothing happens, no message is shown (PB3 is connected to pin6 of CN3, always with SB10 not connected).

[Tesla DeLorean]

Posted on June 06, 2018 at 12:35

The debugger should do the ITM initialization. The core clock must match SystemCoreClock. For stand alone operation the ST-LINK Utilities SWV Window should work with standard firmware.

I tend to use solder on the bridge rather than attempt to jumper.

[Tesla DeLorean]

Posted on June 06, 2018 at 13:04

https://community.st.com/0D50X00009Xkho5SAB

[Davide Michelis]

Posted on June 06, 2018 at 14:15

Ok then, I'm working on a system where I don't have admin credentials so I have to wait before I can install stlink utility. In the meantime I have tried the solution of Jlink (SEGGER RTT) and it works good: Now I would like to know if there is a way to reduce as much as I can the overhead due to tracing: in fact I have noted that when I add the tracing features the system is slowed down in a visible manner (less than UART but still slowed)...

The solution I want investigate so far are:

UART:really bad, slow but always available and simple to configure

ITM+SWO: to be tried

SEGGER RTT: much faster but requires ram overhead and still affects the system

Thanks for the answer and the help.

Best regards.