gpio speed problem

RE: gpio speed problem

hmolesworth — Fri, 02 Dec 2022 16:43:31 GMT

To clarify for William, the cpu clock is different from the i/o pin peripheral clock. Yes the cpu clock can be 64MHz or 128MHz, but the pin peripheral clock is limited to 16MHz regardless of cpu clock so i/o port pin transitions are limited to a shortest interval of 62.5nSec as I noted earlier. Using the DPPI will not increase the peripheral pin clock above 16MHz and so although it will give better stability and predictability the pin can never transition at other than integer multiples of 62.5nSec intervals. The 16MHz i/o pin peripheral clock is synchronous to the 64MHz or 128MHz cpu clock, and so cannot "slide" to other starting positions for the 62.5nSec tick.

RE: gpio speed problem

Kazi Afroza Sultana — Fri, 02 Dec 2022 13:42:53 GMT

Hello William,

I have reproduced the issue and I also have jitter (not stable toggling) for each duty cycle. Since the pins are set with no delay, so we cannot expect stable toggling. To toggle a GPIO without using the CPU, we need to use GPIOTE. CPU and peripheral are on different buses, at different speeds. the peripheral bus is here at 16Mhz, while the CPU is either 128 MHz or 64 MHz.

You need to use either DPPI+TIMER+GPIOTE peripheral or use the PWM peripheral.

You can look at this nrfx sample in zephyr to do that https://github.com/nrfconnect/sdk-zephyr/blob/main/samples/boards/nrf/nrfx/src/main.c .

In prj.conf file, you need to add this CONFIG_NRFX_TIMER2=y also.

Thanks.

Regards,

Kazi

RE: gpio speed problem

William.wei — Fri, 02 Dec 2022 04:47:17 GMT

Thank you Kazi,

Waiting for your reply.

Regards,

William.

RE: gpio speed problem

William.wei — Fri, 02 Dec 2022 04:46:27 GMT

hi,

actually the clock is not 16M when i disable cpu at 128M(which means 64M cpu speed), and this gpio speed is as below:

Regards,

William.

RE: gpio speed problem

Kazi Afroza Sultana — Thu, 01 Dec 2022 06:28:39 GMT

Hello William,

I have reproduced your issue. I will get back to you soon.

Thanks.

Best Regards,

Kazi Afroza Sultana

RE: gpio speed problem

hmolesworth — Wed, 30 Nov 2022 16:42:39 GMT

It is likely that the I/O pin is using the PCLK16M 16MHz clock, so will only transition edges at 62.5nSec intervals. However, I don't see where this is defined in the product spec, or indeed if the PCLK32 or PCLK64 are available for i/o port pin peripheral operation. I/O port pins and PWM may both be limited to 16MHz, whereas TIMER/COUNTER and SPI (for example) can use faster clocks