How to choose serial FIFO and buffer sizes

[Tamás]

Hi All,

What is the recommended way to choose FIFO and buffer sizes for the nrf_serial module? I mean the optimal values for the following constants:

SERIAL_FIFO_TX_SIZE
SERIAL_FIFO_RX_SIZE
SERIAL_BUFF_TX_SIZE
SERIAL_BUFF_RX_SIZE

I use nRF SDK 15.

Thanks,
-Tamás

[Simon]

I am not too sure about this, but I will take a shot anyways. The serial buffer and the serial FIFO are virtual (does not use dedicated hardware), thus are stored in memory and takes up space. The larger values you choose for the constants, the more memory it uses.

When sending some data over UART using the nrf_serial module, the data is first fed into the queue (with size equal to SERIAL_FIFO_TX_SIZE), then it is taken out in chunks (with size equal to SERIAL_BUFF_TX_SIZE). The data chucks is then fed into the function nrf_drv_uart_tx(..) function, which belongs to the UART driver. Thus the smaller values you choose, the more overhead and the more calls to nrf_drv_uart_tx(..) is required.

Regarding size, the optimal values depends on your requirements. If memory is an issue, you should choose small buffer and queue sizes.

Best regards Simon