Posted on March 26, 2014 at 13:01Hi all, your thoughts on this would be appreciated.
I have a need to re-configure the SWCLK pin on the STM32F103C8 (PA14) as an input with pull-up. By default on power up it is input puul-down. I still intend to use as SWCLK for my SW Debug.
I tried reprogramming the GPIOA_CRH and GPIOA_ODR registers to set this, but it had no affect on what the pin physically did.
As an experiment, I changed the MAPR to completely disable JTAG, thus release PA14. Now, changing GPIOA_CRH and GPIO_ODR correctly affects what the pin does.
OK, so I can accept that whilst the JTAG is enabled, that modifying the PulUp/PullDown status may not take affect, but what is strange is that if I:
Disable JTAG
Set PA14 as Pull Up
Re-enable JTAG
then the SWCLK pin retains the state I re-programmed it to.
Indeed after this sequence I can change the mode of the pin as I wish.
So taking this one step further i tried
Disable JTAG
Re-enable JTAG(SWD only)
Modify PA14 input mode
and this works as expected.
So it appears you have to disable jtag, then re-enable before you can modify the input mode of the pin.
This seems very odd does it not?
EDIT
Have now realised that disabling the JTAG pins then re-enabling the SWD pins doesn't work - it appears theat when I do this, the SWD interface is non functional (unless the SWD tries to communicate wilst NRST is active, which I cannot do). Almost as if once you turn the pins off, they remain off until reset!
Nick
#stm32f103-swd-swclk-afio-mapr
