I try to get some debug output using the SWO pin with openocd version 0.10.0+dev-00512-gfd044600 and gdb-multiarch.
I compiled the firmware with the ARMToolchain_8-2018-q4 with the flags --specs=nosys.specs --specs=nano.specs --specs=rdimon.specs, put the function call initialise_monitor_handles(); in the main(). My .gdbinit looks like that:
target extended-remote localhost:3333
monitor reset halt
monitor arm semihosting enable
monitor tpiu config internal ../bin/swo.log
load
break main
I installed the call to ITM_SendChar() in the _putchar() function like that:
void _putchar(char c) { ITM_SendChar(c) };
The chip is STM32L432KC and the openocd command is:
openocd -f board/stm32l4discovery.cfg
When I print "Test\r\n" string I get some extra characters in the swo.log file (output from xxd -b swo.log):
000032e8: 00000001 01010100 00000001 01100101 00000001 01110011 .T.e.s
000032ee: 00000001 01110100 00000001 00001101 00000001 00001010 .t....
The string "Test\r\n" is there but with some extra rubbish. How can I get rid of that?
My workaround now is to cut the nonprintable characters with:
tail -f ../bin/swo.log | tr -cd '\11\12\15\40-\176'
ITM channel can handle 8-, 16- and 32-bit data.
ITM_SendChar() uses 8-bit (1-byte) stream so you have 1 in every other byte as length of subsequent data portion.
For swo.log decoding one can use perl script from this post.