Dubble buffered UARTE reception

RE: Dubble buffered UARTE reception

Thomas — Mon, 21 Oct 2019 18:04:13 GMT

Hi Kasper

Seems I need something very similar to you, Have been struggeling with all the different UART(E) layers for a long time now.

Did you ever find a solution?

RE: Dubble buffered UARTE reception

Kasper Leonhardt — Tue, 25 Jun 2019 10:21:50 GMT

Just like described by Jørgen. I will give it a try.

RE: Dubble buffered UARTE reception

Kasper Leonhardt — Tue, 25 Jun 2019 10:20:46 GMT

Exactly. I will give it a try. I got an unused HW-timer for the purpose. :-)

RE: Dubble buffered UARTE reception

Dmitry — Tue, 25 Jun 2019 09:04:18 GMT

Hi,

to configure double buffering, set ENDRX-STARTRX shortcut and update RXD.PTR to next free buffer on RXSTARTED interrupt (I'm not sure that it can be done with nrf libraries, rather with direct programming of UARTE registers). You should not stop UARTE to manually switch buffers, as you will lose data sometimes. The main problem that you don't know how many bytes actually received. This can be solved by connecting a timer in counter mode to RXDRDY event through PPI - a counter will increment at each received byte.

RE: Dubble buffered UARTE reception

Jørgen Holmefjord — Tue, 25 Jun 2019 06:20:11 GMT

You will get an RXDRDY event when data is received in RXD, but note that the data might not have been transferred to RAM at this point. If you set up and start a timer whenever you start RX for UART, you can use PPI to clear the timer by triggering the CLEAR task. Whenever the timer matches the compare register, you have a pause in your transfer.

RE: Dubble buffered UARTE reception

Kasper Leonhardt — Tue, 25 Jun 2019 05:56:18 GMT

If it was possible to trigger/retrigger a hw-timer each time a byte is recieved, then I have a signal indicating a pause in the reception. If there is a pause it will be for a significant periode.

RE: Dubble buffered UARTE reception

Jørgen Holmefjord — Mon, 24 Jun 2019 15:38:10 GMT

You could write your own driver and use PPI to connect the TO event to the STARTRX task, but this could cause issues and data loss if bytes are received during the timeout period. You will then lose the "up to 4 bytes" that can fit in the HW FIFO if the previous buffer is filled by the first byte, and you do not update the buffer pointer and trigger FLUSHRX before STARTRX.

RE: Dubble buffered UARTE reception

Kasper Leonhardt — Wed, 19 Jun 2019 08:08:18 GMT

The 4 byte HW receive buffer is not much as the soft device has higher priority, and can take the resources in longer time that 4 bytes received on a UART at 921600 baud. I have analysed the behavior when I try to restart the reception after using the RX-abort, when simultaneously receiving data.

"I do not think the double buffering feature is created with variable length transfers in mind.": You are probably right. But I can not be the first one needing this. And I believe that the HW supports it. But the SDK avoids using it.

But it seems to be a problem I must handle elsewhere. :-(

Kasper

RE: Dubble buffered UARTE reception

Jørgen Holmefjord — Tue, 18 Jun 2019 14:29:29 GMT

Hi,

I'm not sure exactly how this should work. The rx_abort function triggers the STOPRX task in the peripheral. The UARTE has a HW FIFO that can receive up to 4 bytes before the TO event. The RX FIFO must be flushed after the timeout, in order to not lose data. There is no shortcut between the timeout event and STARTRX, so you will anyway have to start the RX through using CPU after this event is received.

I do not think the double buffering feature is created with variable length transfers in mind.

Best regards,
Jørgen