PRU R30 jitter

Gigo Dret

Hello,

I'm trying to generate pulses with the fixed duration by PRU on R30 pins on my BBB. I use clpru 2.1.1 for it. Here is my code for polling needed duration:

volatile uint32_t i, m;

..............

pin_high(PIN_GEN);
for (i = 0; i < m; i++);
pin_low(PIN_GEN);

............

void pin_high(uint8_t n) {
__R30 = __R30 | (1 << n);
}

void pin_low(uint8_t n) {
__R30 = __R30 & ~(1 << n);
}

in fact when I want to get 5 us pulse I get it but sometimes pulse is longer (6 or even 7 us).

for some reasons EPWM is not suitable for my task.

I thought that the PRU is jitterless. What is the possible of such behavior?

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi,

I will ask the PRU experts to look at this.

0 Jason Reeder over 9 years ago in reply to Biser Gatchev-XID

TI__Genius 10440 points

Gigo,

Is there a reason that you are specifying variables 'i' and 'm' as volatile? This tells the code that those values could be modified at any time and could cause extra cycles while reading those variables.

If you are just looking to get a 5us delay then you can use the __delay_cycles() function. With the PRU running at 200MHz, each cycle is 5ns. So, you will need to delay 1000 cycles to achieve a 5us delay - __delay_cycles(1000):

pin_high(PIN_GEN);

__delay_cycles(1000);

pin_low(PIN_GEN);

Jason Reeder

0 Gigo Dret over 9 years ago in reply to Jason Reeder

Prodigy 120 points

Hello Jason,

your post helped me to solve the problem. I used __delay_cycles(), also I've replaced function pin_high and pin_low to macroses.

thank you.

0 Jason Reeder over 9 years ago in reply to Gigo Dret

TI__Genius 10440 points

Gigo,

That's good news! Thanks for coming back and verifying the answer.

Jason Reeder

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PRU R30 jitter