direct access of Rx Data in asynchron UART

[Hyun-Young]

Hi

I'm using asynchron UART.

For example, I defined idle time to 20us.

It works without any problem.

#define RECEIVE_TIMEOUT 20

static uint8_t rx_buf[512];

ret = uart_rx_enable(uart ,rx_buf, sizeof(rx_buf), RECEIVE_TIMEOUT);

One disadvantage.

If the message is too long, it takes some time to get event "UART_RX_RDY".

I have a thread, which is called every 1ms.

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)?

kind regard

Hyun-Young

[Håkon Alseth]

Hi,

If the message is too long, it takes some time to get event "UART_RX_RDY".

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

 

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)?

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

[Hyun-Young]

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().

[Håkon Alseth]

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

[Hyun-Young]

Hi

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.

[Håkon Alseth]

Hi,

 

Did you read the UARTE behavior when stopping the RX? 

Håkon Alseth said:

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

Hyun-Young said:

- 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.

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

Hyun-Young said:

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

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