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Missed PWM-interrupts on ADSP21369 / ADSP2136x

Question asked by tonschrat on Jul 8, 2010
Latest reply on Jul 26, 2010 by tonschrat

Hej Engineers,

I'm having an issue dealing propably with missed PLM interrupts on 21369.

For my application, I need to reproduce a PLM-Sequence at low speed precisely. The switching-rate (=frequency of updating the pwm via ISR) is: f_sys=100MHZ devided with the maximum devider of 0xefff, gives f_switch~ 2.54kHz. Should not make too many dificulties.

This works flawlessly for 50-80 cycles, then the ISR does not update the PWM-counter for ~10cycles before it returns to another 50-80cyles of normal operation (and so on). If Optimization is set to max, 2-3 cycles are missed every ~30cycles.

I assumed, there is another (higher) interrupt with higher priority as source for the missed interrupts, so I stripped down my programm to:

- empty main loop

- disable all peripherals except SDRAM

- running from flash to avoid interference from the debugger

- loading the PWM-Values from a circular buffered array from pm

 

The problem is persistend. The statistical profiling gives ~9% execution time for the ISR und ~87% for the interrupt-controller, which sounds a bit weird to me, but may be OK (empty main loop).

 

Init and ISR are written in C. I am using one of the Hardware-PWM-Units, not a general purpose timer. Hardware is rev 3A on EZlite.

Any hint is appriciated.

 

Cheers,

Jan.

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