nrf_delay_us and adc conversion time off by ~ 2X

[Kcecil]

Using nRF52811, Segger SES, and SDK 16.0, I have some times that seem to be off by ~2X.

I'm timing by setting a gpio before and after the event and capturing with a scope.

Using ADC with tacq = 10us, the gpio shows ~23us.

Using nrf_delay_us of 100us, the gpio shows ~230us

nrf_delay_us of 35us, gpio shows ~81us

nrf_delay_us of 10us, gpio shows ~23us.

Using the app timer for waking up from sleep, the delay times are correct.

The SPI clock freq set to 500KHz is also correct.

I've tried both a custom board and the BMD-360 with the same result.

The project is based off the ble_app_template example project.

Any help would be appreciated.  I don't want to just adjust the tacq and nrf_delay_us times to get the correct timing.

[Nguyen Hoan Hoang]

How do you toggle gpio ? to measure 10us delay you need to toggle 5us to 1 and 5 us to 0.  If you do 10us at 1 and 10u at 0, then you get a 20us period. hence the 2X