Timer, GPIOTE, PPI problem

RE: Timer, GPIOTE, PPI problem

Edvin — Tue, 06 Nov 2018 10:17:23 GMT

Hello,

Sorry for the late reply.

I did some testing. Modified your code to use the macros instead of just numbers, so that they are a bit more easy to read. I am having difficulties reproducing what you are seeing.

Can you test the attached main.c file? It is just modified from the project that I attached earlier.

devzone.nordicsemi.com/.../main.c

BR,

Edvin

RE: Timer, GPIOTE, PPI problem

Marc — Thu, 01 Nov 2018 16:09:51 GMT

Edvin,

The difference between my implementation and yours is that you have two timer compare events for each output pin. One for driving the pin high the other for driving it low.

My understanding of the GPIOTE->CONFIG[n] toggle polarity setting was that the pin is toggled (driven high if low or low if high) with TASK_OUT[n]. That's why I have

NRF_PPI->CH[0].EEP = (uint32_t)&NRF_TIMER1->EVENTS_COMPARE[0];

NRF_PPI->CH[0].TEP = (uint32_t)&NRF_GPIOTE->TASKS_OUT[0];

However, it doesn't appear that the toggle mode works in this way. The TASKS_OUT[0] task triggered by the EVENTS_COMPARE[0] event doesn't toggle the pin. Can you explain?

The following modification to my code based on yours works:

NRF_TIMER1->MODE = 0; //timer mode

NRF_TIMER1->BITMODE = 0; //16 bit timer width

NRF_TIMER1->PRESCALER = 4; //16MHz / 2^4 = 1MHz

NRF_TIMER1->SHORTS = 2; //timer cleared at CC[1]

NRF_TIMER1->CC[0] = 1000; //.001 secs

NRF_TIMER1->CC[1] = 2000; //.002 secs

NRF_GPIOTE->CONFIG[0] = (3 | (PIN << 8) | (3 << 16) | (1 << 20)); //task mode, PIN selected, toggle, PIN high initially

//Configure PPI channels 0 and 1 to drive PIN low on every Timer 1 COMPARE[0] match and high on every Timer 1 COMPARE[1] match

NRF_PPI->CH[0].EEP = (uint32_t)&NRF_TIMER1->EVENTS_COMPARE[0];

NRF_PPI->CH[0].TEP = (uint32_t)&NRF_GPIOTE->TASKS_CLR[0];

NRF_PPI->CH[1].EEP = (uint32_t)&NRF_TIMER1->EVENTS_COMPARE[1];

NRF_PPI->CH[1].TEP = (uint32_t)&NRF_GPIOTE->TASKS_SET[0];

NRF_PPI->CHENSET = (1 << 1) | (1 << 0); //enable PPI channel 0

NRF_TIMER1->TASKS_START = 1;

RE: Timer, GPIOTE, PPI problem

Marc — Wed, 31 Oct 2018 17:13:08 GMT

Your code works. I'll compare it to mine.

Thanks for the help

RE: Timer, GPIOTE, PPI problem

Marc — Wed, 31 Oct 2018 16:35:43 GMT

Thanks, Edvin. I'm looking at it now and will let you know.

RE: Timer, GPIOTE, PPI problem

Edvin — Wed, 31 Oct 2018 16:21:11 GMT

Hello,

Just popping by in the end of the day, so I haven't tested your implementation, but I have a similar project that I tested earlier.

devzone.nordicsemi.com/.../ppi_5F00_double_5F00_channel_5F00_pwm.zip

It was written in SDK14.0.0, but if you want it in another SDK, just use the main.c file in your project.

Compare the implementation with yours, and let me know if you are stuck.

Best regards,

Edvin