STM8S interrupt latency

rg1540 · ‎2013-02-11

Posted on February 12, 2013 at 01:29

What is the interrupt latency on STM8S MCUs? I am new to STM8 and the few docs I have read do not mention it.

fggnrc2 · ‎2013-02-11

Posted on February 12, 2013 at 06:41

PM0044 - STM8 CPU Programming Manual - contains the answer.

Figure 2 of Chapter 3 shows that an interrupt takes nine clock cycles to be serviced.

elil · ‎2013-02-14

Posted on February 15, 2013 at 07:15

It's correct but one can see a different time, much larger, due to a problem with ST FW library.

I work with STM8L151, EWSTM8. On entry to RTC wakeup ISR I put a pin toggling and connected oscilloscope probe. Another probe I connected to CCO, routing HSI. MCU is moving to Active Halt mode for a certain time and then - waking up. Looking at the both probes, I saw a difference of 7.5us between the wakeup and getting into RTC ISR, which is the interrupt latency, you're asking about. If the project is built with Cosmic or with IAR, but without ST lib, then, indeed, the mentioned 9 cycles are seen.

rg1540 · ‎2013-02-22

Posted on February 23, 2013 at 04:50

Thanks for your replies.

I found my answer the next day, I guess I was looking in the wrong places 🙂

dyzy · ‎2014-05-27

Posted on May 27, 2014 at 12:38

Dear RobG,

Could you share your solution? I can't find my own. I'm not using ST FW lib at all except header files.

Regards, Dmitry.