STOPRX task of UARTE during reception of bytes

RE: STOPRX task of UARTE during reception of bytes

Remo — Thu, 23 Aug 2018 05:39:40 GMT

Thank you very much for your answer.

RE: STOPRX task of UARTE during reception of bytes

MartinBL — Wed, 22 Aug 2018 12:04:45 GMT

Hi,

As my colleague run_ar says in that thread, there is no exact answer to that because it depends on whether or not other, higher priority, peripherals are using the same DMA channel. However, the system architect says it will occur "within spec". That is, data should be moved out of the FIFO before the next data arrives, so moving one byte should take less time than it takes to receive one byte at whatever baud rate you are using.

RE: STOPRX task of UARTE during reception of bytes

Remo — Wed, 22 Aug 2018 05:24:57 GMT

Thank you for the clarification.

Is it possible that you can make a generous statement about the maximum duration that is necessary to put a byte from the FIFO to the RAM via EasyDMA?

RE: STOPRX task of UARTE during reception of bytes

MartinBL — Thu, 16 Aug 2018 16:16:46 GMT

Hi,

Yes, you are right. If you are only going to check the amounts of received bytes at ENDRX events you may just as well check RXD.AMOUNT rather than using a counter.

The libUARTE library is still in experimental mode, meaning it is still a work in progress (or at least it's not finished). I have asked around and it seems like libUARTE is put on hold for the time being. I imagine that there is/was a thought behind the counter, but it just hasn't been put to full use yet.

RE: STOPRX task of UARTE during reception of bytes

Remo — Tue, 31 Jul 2018 09:50:25 GMT

Thanks for your answer. I assumed that due to the shortcut, the reception would seamless continue in the second RX buffer. Seems that I was wrong. The solution with the PPI channel and the counter sounds promising.

But I don't quite understand why in the nrf_libuarte.c the capture value of the timer is only retrieved when the ENDRX event occurred. Wouldn't it be easier in this case to check the AMOUNTRX value? Is that correct that the capture value could also be retrieved when the reception is ongoing?

In the thread that you've linked they are talking about the number of clock cycles it takes for a received byte to be written from the FIFO to the buffer. I didn't find this information in the product specification. Is there a maximum time that you can state?

RE: STOPRX task of UARTE during reception of bytes

MartinBL — Mon, 30 Jul 2018 16:38:04 GMT

Hi,

I have seen this method been attempted before, but unfortunately it is not possible to start and stop the UART asynchronously like this without concern for the incoming data stream. When you randomly start and stop the UART midstream like this, you will stop the logic, reset DMA channels, etc. at random times and you are bound to lose some bytes.

In SDK 15 we have what we call the Command Line Interface library where one of the available transport layers are the UARTE. If you look in the source code for that ("SDK_folder\components\libraries\experimental_libuarte\nrf_libuarte.c") you can see how the SDK team has chosen to implement something similar. They don't start and stop the UART like this, but use PPI and a counter to keep track of how many bytes are available in the buffer. Maybe you can try something similar.

Here is a relevant thread: https://devzone.nordicsemi.com/f/nordic-q-a/28420/uarte-in-circular-mode