semihosting in stm32f746disco

[mBosc.11]

Hi everyone,

 i want to ask a question about semihosting printing messages in console. I've been using it for some time and it works well. I use it on boards designed by me with various micros and with the ST-LINK/V2 emulator, no problem. I happened to have to use the STM32F746G-DISCO evaluation card, this card already has the emulator integrated on the card... in this case I couldn't get the semihosting to work with console messages. What's different ? Can anyone tell me if he managed to make it work and how?

Thanks

[Peter BENSCH]

You may find the answer in Application Note AN4989, section 7.4.

Hope that helps?

Good luck and regards

/Peter

[Tesla DeLorean]

VCP UART and Pins? SWD PB3 SWO pin? Correct core frequency and HSE_VALUE? 25 MHz not 8 MHz​

[mBosc.11]

thanks for the answer, and the documentation, I checked and did exactly as described, since in other tabs it works.

I found out where the problem is... this micro is an M7 and it has the i cache and the dcache, if I disable these the semihosting works...

But unfortunately I need them because I use ethenet and LWIP, I configured the regions for ethernet (which works). But I don't know what I have to do for semihosting.

can you help me ?

[Tesla DeLorean]

Can only help if you explain method and show related code. Not clear why cache would be a specific issue.

DTCM shouldn't be an issue, not sure how USART would be either.​

Perhaps need to use memory fencing instructions or cache ByAddr maintenance. ​

[Pavel A.]

Confirmed here, with STM32F767 on custom board similar to Discovery-STM32746G.

When D-Cache is NOT enabled, semihosting prints and file opens work well.

After D-Cache enabled, printf prints garbage, opening a file fails.

#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <stdio.h>
extern void initialise_monitor_handles(void);
 
void test_semihosting(void)
{
  initialise_monitor_handles();
  //SCB_EnableDCache(); //<<< if this is commented, semihosting works
  SCB_EnableICache();
  __DSB();
 
  printf("Test semihosting! read big file from host\n");
  char const* fname =  "F:/test/test.bin";
 
  int fd = open(fname, O_RDONLY|O_BINARY);
  if (fd <= 0) {
	  printf("Error open file!\n");
	  return;
  }
......................

 My program runs in RAM, if this matters (and there's another OpenOCD related bug...)