UARTE receive timeout (RXTO)

RE: UARTE receive timeout (RXTO)

Jørgen Holmefjord — Thu, 05 Apr 2018 14:20:05 GMT

Timeouts should be available using the Serial Port library. There are also a new library, nrf_libuarte in the SDK, please see the examples in examples/peripheral/experimental_libuarte directory.

RE: UARTE receive timeout (RXTO)

thefool — Wed, 04 Apr 2018 15:39:56 GMT

Hi Jørgen,
I could not find any direct reference to this in the changelog for SDK15, now that that's out. Is this feature now available in SDK 15?

RE: UARTE receive timeout (RXTO)

Jørgen Holmefjord — Mon, 08 Jan 2018 11:50:32 GMT

Yes, as you see from the timing diagram, there are a possibility that bytes can be received in the timeout period after triggering STOPRX task. If you start a new RX immediately after STOPRX, these bytes will be overwritten in the buffer. The UARTE peripheral support double-buffering, meaning you can setup a new buffer right after receiving TXSTARTED/RXSTARTED events: "The .PTR and .MAXCNT registers are double-buffered. They can be updated and prepared for the next RX/TX transmission immediately after having received the RXSTARTED/TXSTARTED event."

RE: UARTE receive timeout (RXTO)

thefool — Mon, 08 Jan 2018 10:11:23 GMT

is there a risk of losing incoming bytes by calling STOPRX, and immediately starting a new RX, without waiting for the RXTO or ENDRX events? (i.e. what happens if new bytes are coming in during the FLUSHRX task?)

RE: UARTE receive timeout (RXTO)

Jørgen Holmefjord — Mon, 08 Jan 2018 09:38:44 GMT

From the description in the page I linked above, this should explain this: "After the RXTO event is generated the internal RX FIFO may still contain data, and to move this data to RAM the FLUSHRX task must be triggered." It is the FLUSHRX task that triggers the ENDRX event after the RXTO event.

Unfortunately, there is no way of knowing what have been written to RAM by DMA before getting the ENDRX event, indicating that all the data is written and valid.

RE: UARTE receive timeout (RXTO)

GK solutions — Fri, 05 Jan 2018 15:42:49 GMT

In the meantime I was testing something else and noticed that I get the RXTO when I abort...although honestly, I don't really see the point in that, given that we also get the ENDRX event.

On a similar note, is it possible to somehow get the amount of bytes already copied by the dma to our buffer (or pointer to the "head" or something similar) while the DMA is still running, to be able to abort when I get the end of message byte in our protocol? I know the RXD.AMOUNT is only valid (copied from the actual register used) on the ENDRX event. Thanks

RE: UARTE receive timeout (RXTO)

Jørgen Holmefjord — Fri, 05 Jan 2018 14:28:47 GMT

Unfortunately, this has not yet been added to the SDK. We have put some work into this, but it is not completed and tested yet. We previously shared some code in another DevZone thread that might be of interest.

RE: UARTE receive timeout (RXTO)

thefool — Fri, 05 Jan 2018 13:12:36 GMT

So this: "A solution is to connect GPIOTE IN event to the UARTE RX pin and reset a timer when there is any activity on the pin. If the timer reaches a certain timeout, you know that there have been no data received for that time and you can flush the DMA buffer.

We are working on implementing this in the SDK driver."

from here has not yet happened?

RE: UARTE receive timeout (RXTO)

Jørgen Holmefjord — Fri, 05 Jan 2018 11:38:16 GMT

Hi,

RXTO event should only be generated by forced stop via STOPRX task, as shown in timing diagram in Figure 4. UARTE reception with forced stop via STOPRX. Are you triggering the STOPRX task?

Best regards,

Jørgen