When trying to use a cmsis-dap debugger to capture SWO output, I think that the command to change baudrate doesn't send enough bytes to the debug probe. At line 663 of cmsis_dap.c (function cmsis_dap_cmd_dap_swo_baudrate()) it appears that 4 bytes are transferred for this command. I believe it should be 5 total (the command tag 0x19, then the 4-byte baudrate word), as described here <https://arm-software.github.io/CMSIS_5/DAP/html/group__DAP__SWO__Baudrate.html> .
This matches up with an issue I am seeing when using a cmsis-dap probe (to be transparent, this is a probe firmware I am developing myself, and I don't currently have access to a non-custom cmsis-dap probe), where I don't receive a full 4 byte word in the command request buffer from this openocd command; instead the total command length is 4 bytes, the first being the tag and then 3 bytes remaining for the baudrate. OpenOCD Version/Tag: v0.12.0-rc2 Host Probe: custom cmsis-dap firmware Host OS: Windows 10 Target PCB: nucleo l4r5zi Configuration Script: source [find interface/cmsis-dap.cfg] > transport select swd > source [find target/stm32l4x.cfg] > reset_config srst_only srst_nogate connect_assert_srst > $_CHIPNAME.tpiu configure -protocol uart -output swo.out -traceclk > 64000000 -pin-freq 115200 > init > reset run > $_CHIPNAME.tpiu enable
