Bug in app_uart in SDK 10

RE: Bug in app_uart in SDK 10

Primož Kralj — Mon, 21 Mar 2016 11:42:37 GMT

It is still causing HARDFAULTS sometimes, even with the new diff. My app hangs in app_uart_put(): sometimes at app_fifo_put(), sometimes at nrf_drv_uart_tx() and other times it works :(

RE: Bug in app_uart in SDK 10

Susheel Nuguru — Sun, 06 Mar 2016 14:27:12 GMT

This helped me in one scenario, Thanks Petter.

RE: Bug in app_uart in SDK 10

Petter Myhre — Mon, 29 Feb 2016 13:19:17 GMT

Sorry for the late reply.

There is a bug.

But it's not the lack of checking if the FIFO is empty before calling nrf_drv_uart_tx. nrf_drv_uart_tx will return NRF_ERROR_BUSY as long as there is something in the FIFO, since new bytes are fetched from the FIFO and passed to the driver in the interrupt handler.

There is a race condition in app_uart_put. When nrf_drv_uart_tx returns NRF_ERROR_BUSY and the transmission finishes right after that but before the new byte is actually put into the FIFO, then this new byte will linger in the FIFO until app_uart_put is called again (non-empty FIFO won't trigger a new transmission, nrf_drv_uart_tx must be called for this to happen). And the byte passed to this call is transmitted before this one from the FIFO, thus the order is incorrect. This can be observed when some delay is added in app_uart_put, right before app_fifo_put.

This will be fixed in SDK 11 which will be released in the start of March.

For SDK 11.0.0-2.alpha it is possible to replace nrf_drv_uart.c, nrf_drv_uart.h and app_uart_fifo.c with the files from this zip. Here is also the diff with the changes.

RE: Bug in app_uart in SDK 10

Jordan Archer — Fri, 19 Feb 2016 19:28:38 GMT

Any update?

RE: Bug in app_uart in SDK 10

Petter Myhre — Fri, 18 Dec 2015 15:04:26 GMT

Thank you for reporting this. We will look into it and update this when we have something.