Buffering UART data

[ftjandra]

I know this has been asked a couple of times, but I haven't been able to find a straight forward answer.

I have a GPS module that spits out data via UART (no flow control). I would like to have the data stored into a buffer until I am ready to ready read it. The buffer might still be empty, partially filled, or full when I read it. Doesn't matter, I just want to read whatever is there whenever I want. If the buffer gets filled, it's fine if the data gets dropped. I plan to make the buffer big enough that that shouldn't happen, but if it does, doesn't matter.

If it makes a difference, I am running the nRF52840 in a mesh network (Mesh SDK 4.1.0 / SDK 16.0.0). Working off the light switch example.

I've read about using app_uart.c, app_uart_fifo.c, the serial library, etc and am just not sure what to use to accomplish this.

Then there is UART vs UARTE. If I understand what I read correctly, UARTE with EasyDMA can directly put the data in a buffer, but I can't go read it until the buffer is full and not before?

Thanks.

[ftjandra]

Ok, I think I got it working. How do I clear/reset the RX buffer before doing another call to nrfx_uart_rx()?

I did not call nrfx_uart_rx_enable().

I only did nrfx_uart_init() followed by nrfx_uart_rx(). Then when I get the NRFX_UARTE_EVT_RX_DONE event I process the data in buffer and then call nrfx_uart_rx() again. But at this point it looks like the 'overflow' from the past is already partially in the RX buffer. I want to start with an empty buffer.

Thanks.

[Einar Thorsrud]

Hi,

I am sorry for the late reply. The UART Rx is enabled when you call nrfx_uart_rx().It is not possible to clear the buffer in the UART peripheral. (If you used UARTE as you mentioned before that would be different since the peripheral copies data into RAM using DMA).

[ftjandra]

Oops, I mistyped. I am using nrfx_uarte_init() and nrfx_uarte_rx().

And, I was on the wrong infocenter page when I was reading about nrfx_uart_rx_enable(), which I see has nothing to do when using UARTE.

Thanks.

[ftjandra]

Still trying to figure out how to clear the RX buffer when using nrfx_uarte so that it starts with an empty buffer on calling nrfx_uart_rx().

Thanks.

[Einar Thorsrud]

Hi,

In this case, the Rx data is copied into normal RAM, so I assume that is what you refer to as the RX buffer in this case? If so, and you want to initialize it, you would just need to use memset() on the buffer before calling nrfx_uart_rx().