Calling a SWI_post takes too much CPU time

DSP_KungFu_Master

Hello,

I have a hardware INT1 interrupt executed 8000 times per second. Inside the interrupt if some conditions are met I call SWI_post().

When that happens I can see that the normal interrupt execution time which is exactly 12uS gets extended to 30-65uS (random value), which takes almost half of my inter-sample time..

Can anyone answer why is calling a SWI_post() taking so much time?

I did try a simple test and I removed all the code in the SWI routine which is associated with the SWI_Post(). In that case SWI_post() takes very little time. How is this related?

It looks like when I do SWI_post() then SWI routine gets executed immediately and then code returns to INT1 interrupt, which should not happen since INT1 has highest priority and should not be interrupted.

Any ideas?

over 13 years ago

0 DSP_KungFu_Master over 13 years ago

Intellectual 705 points

Hello,

I just confirmed that calling SWI_Post executes the SWI routine immediately. How can I prevent this? I tried using SWI_Disable at the beginning of int1 and SWI_Enable at end but still SWI is being executed immediately after SWI_post.

Please help!

0 ScottG over 13 years ago in reply to DSP_KungFu_Master

TI__Mastermind 26780 points

To call SWI_post() from an ISR you need to either use the HWI_enter/HWI_exit macros, or the HWI dispatcher. These will prevent the SWI scheduler from immediately switching to the posted SWI - within the HWI context - which you are observing.

This is described in section 4.2 “Hardware Interrupts” in the DSP/BIOS User’s Guide (http://www.ti.com/lit/ug/spru423h/spru423h.pdf).

Scott

0 DSP_KungFu_Master over 13 years ago in reply to ScottG

Intellectual 705 points

Great! I tested the solution and it works!

You are the man!

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Calling a SWI_post takes too much CPU time