SWD调试在STM32中REMAP调试的深入探究

rookie 2019-08-14

展开全文

首先说一下问题的现象，如果有这种现象的同学可以看看博主的这篇博文

程序download一次后，第二次download就提示no target connect，除非长按reset键才能继续下载程序

首先上一组stm32的TIM2的端口使用组合有下面四种：

1.当不重映射时，默认TIM2四个的IO口是PA0、PA1、PA2、PA3

开启重映射__HAL_AFIO_REMAP_TIM2_ENABLE()

2.要使用PA15、PB3、PA2、PA3的端口组合，要调用下面的语句进行部分重映射：

__HAL_AFIO_REMAP_TIM2_PARTIAL_1()

3.要使用PA0、PA1、PB10、PB11的端口组合，要调用下面的语句进行部分重映射：

__HAL_AFIO_REMAP_TIM2_PARTIAL_2()

4.要使用PA15、PB3、PB10、PB11的端口组合，要调用下面的语句进行完全重映射：

__HAL_AFIO_REMAP_TIM2_ENABLE()

同时还要禁用JTAG功能，PA15、PB3、PB10、PB11才会正常输出。

那么使用了重映射之后会导致一个问题，程序download一次后，第二次download就提示no target connect，除非长按reset键才能继续下载程序。

该问题讨论可在此问答中找到答案

https://electronics./questions/260757/timer1-remap-cause-debug-crash-on-stm32f103

从该帖子找到的精辟回答如下

The problem is that the STM32F1 series has one register AFIO_MAPR which contains thesettings for remapping various peripherals and for enabling/disabling the JTAG/SWD connectionto your debugger. And to makethis more complicated, the bits in that register which enable/disable theJTAG/SWD settings (bits 24-26) arewrite-only so their existing state cannot be read.

See this extract from the STM32F1Reference Manual:

This means that any attempt to change the settings of thevarious "peripheral remap" bits, by doing a read-modify-writesequence to this register, could read differentvalues instead of the real current valuesin the JTAG/SWD bits. Then, when the write to the register is done, your debugger access stopsbecause whatever was read from those JTAG/SWD bits, is written back to them.(Other effects have also been reported, but I won't go into that now).

From what I could find without installing the HAL, the macrosused are:

#define __HAL_AFIO_REMAP_TIM1_ENABLE() MODIFY_REG(AFIO->MAPR, AFIO_MAPR_TIM1_REMAP, AFIO_MAPR_TIM1_REMAP_FULLREMAP)

and MODIFY_REG is:

#define MODIFY_REG(REG, CLEARMASK, SETMASK) WRITE_REG((REG), (((READ_REG(REG)) & (~(CLEARMASK))) | (SETMASK)))

So as you see, MODIFY_REG isdoing a read-modify-write and you don't know what values it will read fromJTAG/SWD bits 24-26 andhence what values it will write back to there! The values read from those bitsare "undefined" (to quote ST) and I know I have read different valuesfrom the same STM32F1 at different times.

The "fix" I have used with the SPL, is to change anyremapping code to specifically set the JTAG/SWD bits which you want, wheneveryou write to the AFIO_MAPRregister. You will need to figure out how you want to do the same with the HALcode. One way is to use a temporary variable so, from memory, the sequencebecomes:

· Read AFIO_MAPR register intotemp variable

· Change desired peripheralremap bits in the temp variable

· Mask out bits 24-26 in thetemp variable

· Set bits 24-26 in the tempvariable to whatever I wanted (therefore ignoring whatever their, likelyincorrect, "read" value was)

· Write temp variable toAFIO_MAPR

基本上导致这个问题的原因在于SWJ_CFG[2]位是Write Only的，
__HAL_AFIO_REMAP_I2C1_ENABLE()中会执行类似reg |= xxx_enable的操作
该操作会读寄存器，然后或上某个使能位
然而由于SWJ_CFG[2]位的Write Only特性，导致寄存器读出来后不是实际的值

解决方法：在使用了引脚复用的宏之后需要调用一次__HAL_AFIO_REMAP_SWJ_NOJTAG()，该宏的解释如下：

/**

* @brief Enable the Serial wire JTAG configuration

* @note NOJTAG: JTAG-DP Disabledand SW-DP Enabled

* @retval None

#define__HAL_AFIO_REMAP_SWJ_NOJTAG() do{CLEAR_BIT(AFIO->MAPR, AFIO_MAPR_SWJ_CFG); \

SET_BIT(AFIO->MAPR, AFIO_MAPR_SWJ_CFG_JTAGDISABLE); \

}while(0U)

我们追一下CLEAR_BIT(AFIO->MAPR,AFIO_MAPR_SWJ_CFG);

可以发现#defineCLEAR_BIT(REG, BIT) ((REG) &=~(BIT))

继续追该宏使用的参数AFIO->MAPR,AFIO_MAPR_SWJ_CFG，其中MAPR为复用寄存器，而AFIO_MAPR_SWJ_CFG追到最后为0x07000000(过程比较多，就不赘述了)，再通过&= ~(BIT)操作，得出&=~(0111000000000000000000000000)

最后结果为&=11111000111111111111111111111111