high speed control interrupt with RTOS

Justin Walraven

Hi Everyone!

I've been playing around with TI-RTOS, and it's wonderful for development! However, I need to run an interrupt at 200kHz (5us) for control, so the 10us latency inherent in the BIOS on the F28069 at 90Mhz for interrupts simply won't work. I've taken the interrupt out of the RTOS with Hwi_plug, and the latency seems to be better, but the jitter is now up at about 1us. In bare metal, the jitter is a fraction of that.

The conclusion that I've come to is that the timer2 interrupt that the RTOS uses is pre-empting my timer0 interrupt, and the timer1 interrupt seems to be locked out. Even if it wasn't, I need to be able to use lower priority PIE level interrupts like PWM and ADC.

http://www.ti.com/lit/an/spraax9/spraax9.pdf

This app note for this indicates that the worst case lock out is 88 cycles, or .97us, which is exactly what I saw.

Is there any way to make it so that the RTOS doesn't lock me out of my control interrupt for a variable time?

Justin

over 10 years ago

0 ToddMullanix over 10 years ago

TI__Guru* 96960 points

Hi Justin,

There are a couple things that you can try.

1. Configure the kernel to not use a timer. Instead you can have it be basically tickles (so you cannot do timeouts/sleeps with a value other than 0 or BIOS_WAIT_FOREVER).

2. Configure the kernel to not use a timer but you drive the Clock by calling Clock_tick instead. This allows you to use timing services in the kernel. Note: you cannot make kernel calls from an interrupt that is not managed by the kernel though.

Todd

0 Justin Walraven over 10 years ago in reply to ToddMullanix

Intellectual 300 points

Thanks Todd!

Um... how would I do the second?

Justin

0 ToddMullanix over 10 years ago in reply to Justin Walraven

TI__Guru* 96960 points

You can have your non-kernel managed timer interrupt trigger an kernel managed interrupt that calls Clock_tick().

To have the kernel not use a timer, set the following in the .cfg file (or do it graphically on the Clock Module page)

Clock.tickSource = Clock.TickSource_USER;

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high speed control interrupt with RTOS