Interrupt Execusion Time

billstrong said:

1. Is  the time between an interrupt initiated and the isr executed fixed?

Bill,

I find this useful when talking about interrupt latency - it is taken from the Delfino workshop:

http://processors.wiki.ti.com/index.php/C2000_Delfino_Multi-Day_Workshop

The actual maximum latency will change, as indicated in the image.  Things that can delay an interrupt:

• Are interrupts disabled (INTM)?   When you take an interrupt this is automagically done - so to allow nested interrupts it has to be cleared.
• Is the CPU executing a RPT instruction (single repeat).  This cannot be interrupted.
• Multiple cycle instructions - for example, if the CPU was just executing a loop - each time through the loop a branch would be taken which could delay an interrupt for 4 cycles.   One way to avoid this is to put the CPU into idle so it will be in the same state each time the interrupt comes in.
• Is code execution in waitstated memory
• Is stack in waitstated memory - rare that we have data memory with a waitstate in c2000 but say, just as a weird example, the stack was in external memory (XINTF).
• Is the stack and the code in the same physical memory block

Hope this helps

Lori