direct access of Rx Data in asynchron UART

RE: direct access of Rx Data in asynchron UART

Håkon Alseth — Mon, 17 Jun 2024 09:16:10 GMT

Hi,

Did you read the UARTE behavior when stopping the RX?

[quote userid="2115" url="~/f/nordic-q-a/111826/direct-access-of-rx-data-in-asynchron-uart/487501"]

The reason why it takes longer when you're actively receiving data is due to how the hardware peripheral works:

https://docs.nordicsemi.com/bundle/ps_nrf52840/page/uarte.html#ariaid-title4

[/quote]

[quote userid="116449" url="~/f/nordic-q-a/111826/direct-access-of-rx-data-in-asynchron-uart/489029"]

- I have to read DMA from UART Rx every 1ms.

Problem is if I use asynch, the Call Back Event occurs after the idle time expires.

[/quote]

You can potentially be blocked by higher priority threads, thus this might be skewed in time.

[quote userid="116449" url="~/f/nordic-q-a/111826/direct-access-of-rx-data-in-asynchron-uart/489029"]Problem is if I use asynch, the Call Back Event occurs after the idle time expires.[/quote]

This is also expected, as a reception is timed out after 1 ms, and if there's more bytes; the above linked UARTE behavior will also skew your timing.

If I've understood you correctly; It sounds like you need to do polling per-byte, not use the async UART library functionality, as you want to fetch each byte as quick as possible for processing.

Kind regards,

Håkon

RE: direct access of Rx Data in asynchron UART

Hyun-Young — Mon, 17 Jun 2024 08:50:06 GMT

I think, you don't understand what I want to do.

What I want to just do:

- I have to read DMA from UART Rx every 1ms.

Problem is if I use asynch, the Call Back Event occurs after the idle time expires.

It can be less than 1ms or more than 1ms.

Is there any function just like "dma_get_data(UART)"?

Thank you.

RE: direct access of Rx Data in asynchron UART

Håkon Alseth — Fri, 07 Jun 2024 11:55:40 GMT

Could you explain in detail what you're trying to achieve?

The behavior, in terms of event process, of the uart async API is described in the docs here:

https://docs.zephyrproject.org/latest/hardware/peripherals/uart.html#asynchronous-api

Do I understand correctly when you always want to return every 'n' ms? If yes, is there a specific reason why?

Normally, one would run the serial communication in a dedicated thread, which then yields for the remainder of the system, and combined with a signalling/k_poll functionality; you can share the communicated data on-demand between threads/functions.

Kind regards,

Håkon

RE: direct access of Rx Data in asynchron UART

Hyun-Young — Fri, 07 Jun 2024 06:46:16 GMT

Do you mean, I can call "uart_rx_enable(..)" every 1 ms? Doesn't it disturb the running receive buffer? I thought, I may call uart_r_enable() either at beginning or after uart_rx_disable().

RE: direct access of Rx Data in asynchron UART

Håkon Alseth — Wed, 05 Jun 2024 11:54:05 GMT

Hi,

[quote user=""]If the message is too long, it takes some time to get event "UART_RX_RDY".[/quote]

The reason why it takes longer when you're actively receiving data is due to how the hardware peripheral works:

https://docs.nordicsemi.com/bundle/ps_nrf52840/page/uarte.html#ariaid-title4

[quote user=""]

In that thread, I want to check Rx-Data for example every 1ms.

How can I get the data and length every 1ms ?

Zephyr offers just one trigger "idle time".

Is there any other trigger for example (every X ms)?

[/quote]

You can run the uart_rx_enable in a dedicated thread, with a timeout of 1 ms for instance. Or am I misunderstanding your scenario here?

Kind regards,

Håkon