UART receive in background without callback on nRF52 SDK11

[puz_md]

Hi, I'm looking for an easy way to use the UART in blocking mode (or something similiar) with a receive buffer that is filled in background:

• If possible using EasyDMA for better performance and easier software design
• TX data may either block until all data has been sent or may return immediately and provide an additional function call to check if all data has been sent successfully.
• RX data shall received in background and stored in a buffer/FIFO. It shall be possible to read data of arbitrary size from the receive buffer without stopping reception.
• No callbacks or event handlers shall be used (synchroneous control flow in application).

In the past, on the nRF51, we used the app_uart library with FIFO support. Looking at the SDK11 documentation on infocenter.nordicsemi.com, I couldn't find any information about this library (although the directory is still there in the SDK11 archive). Is app_fifo still working on SDK11 on nRF52? Does it take advantage of the EasyDMA feature?

Looking at nrf_drv_uart.h, double buffering is mentioned to provide support for continuous data reception in non-bocking mode. But what does happen if the last received data byte does not fill the buffer to 100%? Will the driver wait for more bytes until the buffer is full, not giving any opportunity to receive data from the partially filled buffer? In other words, is there any possibility to receive "byte streams" of arbitrary length using UART with EasyDMA (something like app_uart with FIFO feature using EasyDMA)?

[puz_md]

@bat13: That's the idea I had myself. It would be nice if after a RX abort, if the second buffer would immediately be activated. Just try it out and give me some feedback if it works ;-) Although I fear there is a small risk that data may be lost while the EasyDMA buffers are updated by the driver (maybe they will have to trigger the STOP task, update the buffer, and trigger the START task again. And data transmitted within this interval gets lost.

I have another Idea that I would like to try out: I suppose there shuold be a register containing the current offset within the EasyDMA RX buffer. If this register is readable by software, application code can find out how many bytes have already been received in the current buffer. If you use two adjacent buffers, you could treat them as a circular FIFO and update head and tail each time a RX complete event is triggered. But you can also update the tail and read out some bytes from the active buffer before the event is triggered if you can find out the EasyDMA state. Altough you have to make sure that there are no race conditions when updating the tail (different control flows!). In short, that's what I would like to implement, If I can get some time for this.