nRF52840 flow control

RE: nRF52840 flow control

Kenneth — Thu, 08 Mar 2018 09:51:22 GMT

How about just supplying a large fixed buffer, e.g. 512bytes, and then the application may just read the RAM location directly? Of course the application then would possible need to handle the case that some bytes in a response may be written at the end of the buffer and continue at the start of the buffer (because the messages likely won't fit exactly in the 512bytes), but I don't expect that is a big problem.

RE: nRF52840 flow control

KV — Wed, 07 Mar 2018 21:17:33 GMT

Thanks for the response. This was very helpful. So my application is command/response communication scheme between master and slave. Size of response depends on the command sent. So would the sequence of TX/RX using the APIs would be as below. I had to call the rx_abort between one TX and the next. Otherwise, the size of buffers gets out of sync.

uint8_t rx_byte[256];
while(1)
{
	// Command 1 (8 byte), Resp 1 (16 bytes)
	while(NRF_SUCCESS != nrf_drv_uart_tx(&app_uart_inst, command_1, 8) );   
	while( NRF_ERROR_BUSY != nrf_drv_uart_rx(&app_uart_inst, rx_byte, 16));
	while( NRF_ERROR_BUSY != nrf_drv_uart_rx(&app_uart_inst, rx_byte, 16));
	if(err_code != NRF_ERROR_BUSY)
	{
		APP_ERROR_CHECK(err_code);
	}       

	nrf_delay_ms(300);

	nrf_drv_uart_rx_abort(&app_uart_inst); // generates a RXDONE event - ignore
	
	// Command 2 (4 byte), Resp 1 (128 bytes)
	while(NRF_SUCCESS != nrf_drv_uart_tx(&app_uart_inst, command_2, 4) );   
	while( NRF_ERROR_BUSY != nrf_drv_uart_rx(&app_uart_inst, rx_byte, 128));
	while( NRF_ERROR_BUSY != nrf_drv_uart_rx(&app_uart_inst, rx_byte, 128));
	if(err_code != NRF_ERROR_BUSY)
	{
		APP_ERROR_CHECK(err_code);
	}       

	nrf_delay_ms(300);

	nrf_drv_uart_rx_abort(&app_uart_inst); // generates a RXDONE event - ignore
			
}

RE: nRF52840 flow control

Kenneth — Wed, 07 Mar 2018 15:56:55 GMT

Hi, if you enable EasyDMA (sdk_config.h) and use the driver directly you should be able to do this without loosing any data. I recommend to always call nrf_drv_uart_rx() until NRF_ERROR_BUSY, this way you ensure the secondary buffer is always ready to receive data when the first is full. Also you should set the buffer length to more than 1, e.g. >10.