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HAL_AFIO does not handle changes to JTAG/SWD properly

Question asked by brestel.dean.001 on Nov 22, 2017
Latest reply on Mar 22, 2018 by Imen D

At least on the SMT32F103x parts, the SWJ_CFG bits in the AFIO_MAPR register are write only.  Reading these bits is undefined.  All of the __HAL_AFIO_REMAP macros in stm32f1xx_hal_GPIO_ex.h do read/modify/write operations to this register.  This can cause wild behavior.


For example, on the STM32F103VET6:





This first sets AFIO_MAPR to 0x02000000 to disable the JTAG pins.  Then, while remapping TIM4 it sets AFIO_MAPR to 0x04001000 which both remaps TIM4 and completely disables JTAG and SWD.  This happens because the undefined read of the SWJ_CFG bits gets written back to the AFIO_MAPR.


Workaround are to cache the state AFIO_MAPR locally and write that, or use the Bit-Band memory to operate on individual bits.