Posted on November 26, 2016 at 15:52
When debugging an application I wondered about a strange value in
TIM8_DMAR
that I had not written there intentionally. In the end it all boiled down to an invocation of
LL_TIM_SetCounterMode (TIM8, LL_TIM_COUNTERMODE_DOWN)
:
822 LL_TIM_SetCounterMode (TIM8, LL_TIM_COUNTERMODE_DOWN);
(gdb) s
LL_TIM_SetCounterMode (TIMx=0x40013400, CounterMode=16) at /home/h/STM32Cube/Repository/STM32Cube_FW_L4_V1.5.2/Drivers/STM32L4xx_HAL_Driver/Inc/stm32l4xx_ll_tim.h:1467
1467 MODIFY_REG(TIMx->CR1, TIM_CR1_DIR | TIM_CR1_CMS, CounterMode);
(gdb) p/x &TIMx->CR1
$27 = 0x40013400
(gdb) p/x TIMx->CR1
$28 = 0x0
(gdb) p/x &TIMx->DMAR
$29 = 0x4001344c
(gdb) p/x TIMx->DMAR
$30 = 0x0
(gdb) s
1468 }
(gdb) p/x TIMx->CR1
$31 = 0x10
(gdb) p/x TIMx->DMAR
$32 = 0x10
(gdb)
After stepping into (line 2) I checked addresses and contents of the peripheral registers
TIM8_CR1
and
TIM8_DMAR
(lines 5 to 12). Everything behaved as expected. No bad defined structures and the contents were still at their reset values. However, the next step (line 13) changed
TIM8_DMAR
to the same value as
TIM8_CR1
(line 18). I checked the definition of
MODIFY_REG
, but it was reasonable:
1.
#define WRITE_REG(REG, VAL) ((REG) = (VAL))
2.
#define READ_REG(REG) ((REG))
3.
#define MODIFY_REG(REG, CLEARMASK, SETMASK) WRITE_REG((REG), (((READ_REG(REG)) & (~(CLEARMASK))) | (SETMASK)))
What is happening here?
#stm32l476rgt6u
