Data got by calling the k_fifo_get() less than the data received by the UART RX

[Tom.Fu]

Dear Support Team

I test the peripheral_uart sample from NCS(V2.4.0), I found that the data got by calling the k_fifo_get() less than the data received by the UART RX. For example, I sent 208 Bytes to the UART RX but it just printed 200 Bytes by calling the LOG_HEXDUMP_INF()  macro as the screenshots below showing, and UART baud rate I set is 921600.

Below screenshot below shows I send 208 Bytes to the RX. This packet starts with 2c and ends with 2c.

Below screenshot shows the data printed by calling the LOG_HEXDUMP_INF()  macro. It starts with 2c but ends with 77, so there was still 8 bytes haven't been printed.

Why it would loss printing the 8 bytes? How could I print all of the any size of data packet without end with \r or \n received by the UART RX?  Many thanks.

[Sigurd]

Hi,

It might not be printed until the RX buffer is full, or until timeout(https://github.com/nrfconnect/sdk-nrf/blob/main/samples/bluetooth/peripheral_uart/Kconfig#L30C8-L30C32), 50 seconds default.

Try e.g. sending 240 bytes, and see if everything is printed. or maybe try reducing CONFIG_BT_NUS_UART_RX_WAIT_TIME

[Tom.Fu]

Dear Sigurd

I configured the CONFIG_BT_NUS_UART_RX_WAIT_TIME  with value 50, it could print all the 240 bytes after PC sent 240 bytes to UART RX., but it was still loss printing the 8 bytes after PC sent 208 bytes to UART RX.

Is there any other way to get all the data of any size sent to UART RX of nRF52832? Many thanks.

[Jørgen Holmefjord]

Hi,

Tom.Fu said:

Is there any other way to get all the data of any size sent to UART RX of nRF52832? Many thanks.

The timeout should handle this, as long as the data is not sent too fast so it is lost because there is no available buffer.

If you first send 208 bytes, then 32 more bytes afterwards, are you still losing the 8 bytes?

Best regards,
Jørgen

[Ramulous]

I'm having a similar problem.  Either the buffer has to fill up or the timeout has to occur.  If I send a shorter amount of bytes even with \r\n I still have to wait for the timeout.  As a workaround I significantly decreased the timeout CONFIG_BT_NUS_UART_RX_WAIT_TIME  which is a huge improvement but its not the optimal solution.  Race conditions and other nasty things can occur if not careful.  Ideally the data will show up immediately after the \r\n or something.  The way I'm seeing it the data only shows up with either all the data is sent or the timeout.  If that's not correct please let me know.  I think the original post I think maybe Tom Fu has a valid complaint and just reducing the timeout although is a big help its more of a bandage to me and a good solution should come forward.

[Jørgen Holmefjord]

Hi,

Unless you know the exact size of the string before \r\n arrives, it is not possible to get the data before a timeout. The HW does not have any way to know when these characters are received, and it can therefor not inform the application before a timeout occurs. The other alternative is to use only 1 byte buffers for all UART transfers and check each received byte in SW, but this will cause heavy load on the CPU and is not feasible with high throughput on the UART. This will be a tradeoff that the designer makes in the application (frequency of interrupts vs. latency from transfer end until application interrupt).

Best regards,
Jørgen