delay introduction and example stm32f407

[mohamad_armoon]

Posted on June 29, 2014 at 10:04

hi guys i have discovery board (stm32f407) and in my code i have some tasks which have to execute in specific time . so i have to have a accuratedelay , i used to use this :

void
Delay(__IO uint32_t nCount)
{
while
(nCount--)
{
}
}

but i think it's not accurate , i need a function to specify this by millisecond. can you explain how many methods is there to do that and make an example ?? thank

[Tesla DeLorean]

Posted on June 29, 2014 at 12:32

Well there are a lot of reasons it can be unpredictable, like interrupts and cache (tight loops probably not so much). To generate exact timing one should try to use hardware.

To make a spin loop more predictable consider using a free running counter, like DWT_CYCCNT

https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/compensating%20latencies%20on%20STM32F4%20interrupts&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B&cu...

Pass in clock ticks in processor clocks. 1 second = SystemCoreClock, 1 ms =SystemCoreClock / 1000, ideally using a constant You might want to calibrate the loop finely as it acts more like f(x) = mx + c