CONFIDENCE & CONFIG Settings

[Jim Logsdon]

Each time I attempt to use a Zephyr API on my NORDIC device, I face the mystery of what CONFIG setting are required to go with it.  For example:

To make the Async UART API work, I consulted the Nordic's API page: docs.nordicsemi.com/.../group_uart_async.html

It doesn't mention any CONFIG settings.   After a GOOGLE search, I found a user that said these CONFIG settings are required:

#For UART

CONFIG_SERIAL=y

CONFIG_UART_ASYNC_API=y

CONFIG_UART_0_ASYNC=y

CONFIG_UART_0_NRF_HW_ASYNC=y

CONFIG_UART_0_NRF_HW_ASYNC_TIMER=2

CONFIG_NRFX_TIMER4=y

And sure enough, that made it work.   Out of curiosity, I commented out all but two of those, and it still seems to work.  I think?

#For UART

CONFIG_SERIAL=y

CONFIG_UART_ASYNC_API=y

#CONFIG_UART_0_ASYNC=y

#CONFIG_UART_0_NRF_HW_ASYNC=y

#CONFIG_UART_0_NRF_HW_ASYNC_TIMER=2

#CONFIG_NRFX_TIMER4=y

My point is that I'm "guessing" at CONFIG settings, hoping that they are correct.  That is not engineering. 

How can I take the guess work out of using Nordic with Zephyr when it comes to CONFIG settings?

Thank you

 

[Håkon Alseth]

Hi,

 

For the device that you use, which seems to be a nRF52832, that only has one UART instance, it will automatically select that instance if this is set:

CONFIG_UART_ASYNC_API=y

Then this is default y:

CONFIG_UART_0_ASYNC=y

However, these are not default y:

CONFIG_UART_0_NRF_HW_ASYNC=y

CONFIG_UART_0_NRF_HW_ASYNC_TIMER=2

As the first one does not have a default 'y' in its definition:

https://docs.nordicsemi.com/bundle/ncs-latest/page/kconfig/index.html#CONFIG_UART_0_NRF_HW_ASYNC

Nor does the async timer instance:

https://docs.nordicsemi.com/bundle/ncs-latest/page/kconfig/index.html#CONFIG_UART_0_NRF_HW_ASYNC_TIMER

 

So, why is there multiple configurations here? The problem lies with the NRF_UARTE peripheral itself.

https://docs.nordicsemi.com/bundle/ps_nrf52832/page/uarte.html#d955e183 

It does not give you the "on-going" amount of bytes received directly in hardware (nRF54L-series gives this in the UARTE.RX.CURRENTAMOUNT register), so to be able to count the amount of bytes you're receiving, you need to use the byte-for-byte event RXDRDY.

 

By looking at the configuration for the "_HW_ASYNC" feature, it uses dedicated hardware peripherals (PPI and TIMER instance) to count the incoming bytes as compared to using k_timer instance(s) for timeout.

The UARTE hardware peripheral on nRF52832 will effectively be able to count each incoming byte with the RXDRDY event, and using a TIMER to count + PPI will be more efficient (and accurate) as compared to manually incrementing a byte-counter variable in a ISR.

 

If you have a TIMER instance available, the best option is to enable:

CONFIG_UART_0_NRF_HW_ASYNC=y

CONFIG_UART_0_NRF_HW_ASYNC_TIMER=2

I agree with your conclusion:

My point is that I'm "guessing" at CONFIG settings, hoping that they are correct.  That is not engineering. 

The choices that you are presented with are not explained properly, which I will bring up internally.

  

Kind regards,

Håkon

[Jim Logsdon]

Thank you