PA13 used as USR_SW conflicts with SW debug

[dpgeorge]

Originally opened by @jevers76: When the software initializes PA13 as an input for USR_SW it's use as SWDIO ends. The chip must be erased before SW debbug can be used again. This makes debugging with a jtag or SW like the stlink 2 difficult. Can the PCB be changed? One alternative to changing the PCB would be to only init the pin when needed by calling some py function.

[iabdalkader]

Hi, there's a bit you can check to see if the debugger is attached, maybe something like this can be used as a workaround:

if (CoreDebug->DHCSR & CoreDebug_DHCSR_C_DEBUGEN_Msk) {
    //configure PA13 for SWD
    GPIO_InitTypeDef GPIO_InitStructure;
    GPIO_InitStructure.GPIO_Pin = PYB_USRSW_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_Init(PYB_USRSW_PORT, &GPIO_InitStructure);
    GPIO_PinAFConfig(PYB_USRSW_PORT, PYB_USRSW_PIN, GPIO_AF_SWJ);
} else {
    //use PA13 as user switch
    sw_init();
}

I tried it and it kinda works, but it needs some delay for the debugger to be detected...

See:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka14536.html

[hagenkaye]

It would be nice if the switch was moved to another pin.

I was inspired by your post. So I dug up my bus pirate and thought - "gee I wonder if I can use it to debug the micro python board". After some fiddling, I got debugging to work.

Pins needed by bus pirate to run as a jtag debugger

PA13 - TMS
PA14 - TCK
PA15 - TDO
PB3 = TDI