Posted on March 12, 2014 at 16:05Setup:
I've just generated code for stm32f407 using the latest STM32CubeMX. Here's the generated code for delay function in file stm32f4xx_hal.c:
void HAL_Delay(__IO uint32_t Delay)
{
uint32_t timingdelay;
timingdelay = HAL_GetTick() + Delay;
while(HAL_GetTick() < timingdelay)
{
}
}
It's fairly simple,
HAL_GetTick
returns a value of
uwTick
- variable that is incremented in SysTick interrupt handler.
Bug Description:
When the value of variable
uwTick
becomes large enough (i.e. adding Delay will overflow uint32) delay function will not work correctly, because expression ''
HAL_GetTick() < timingdelay
'' will immediately be false.
That results in no delay at all.
Example: Consider
uwTick = 0xFFFF FF00
and
Delay = 0x101
Then
:
timingdelay = 0xFFFF FF00 + 0x101 == 0x01
Then
while(HAL_GetTick() < timingdelay)
is
(
0xFFFF FF00
< 0x01 ).
This is already false and while is not executed. No delay is performed!
Comment:
This bug can be real pain, because it will work only when overflow of
uwTick
is near (or delay is really large). If one had
uwTick
incremented every millisecond (seems to me like a reasonable value), bug
can accure in about 47 days from reset.
Solution:
That's easy enough:
uint32_t startTime = HAL_GetTick();
while( HAL_GetTick() - startTime <= Delay);
If we compare the differencies between moments of time and Delay - we are okay (as long as Delay is not bigger than
0xFFFF FFFF
, but that's sort of unrealistic and can be guaranteed by assert); overflow will not affect it.
#bug-stm32-timeout-hal_gettick #bug #hal #hoist-by-their-own-petard #spl
