nRF52DK nRF52832 UART asynchronous receive

[zazas321]

I am working through the Nordic Developer Academy and got stuck at lesson 4 (UART receive)

https://academy.nordicsemi.com/courses/nrf-connect-sdk-fundamentals/lessons/lesson-4-serial-communication-uart/topic/uart-driver/

In particular, I am confused about this part:

I have created a sample project and connected external CP2102 USB->Serial adapter to P0.06 and P0.08 pins.

The code that I use:

/*
 * Copyright (c) 2012-2014 Wind River Systems, Inc.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr/kernel.h>
#include <zephyr/drivers/gpio.h>
#include "stdio.h"
#include "zephyr/drivers/uart.h"

const struct device *uart = DEVICE_DT_GET(DT_NODELABEL(uart0));

static uint8_t tx_buf[] =  {"nRF Connect SDK Fundamentals Course \n\r"};
static uint8_t rx_buf[10] = {0}; //A buffer to store incoming UART data 

const struct uart_config uart_cfg = {
		.baudrate = 115200,
		.parity = UART_CFG_PARITY_NONE,
		.stop_bits = UART_CFG_STOP_BITS_1,
		.data_bits = UART_CFG_DATA_BITS_8,
		.flow_ctrl = UART_CFG_FLOW_CTRL_NONE
	};

static void uart_cb(const struct device *dev, struct uart_event *evt, void *user_data)
{
	switch (evt->type) {
	
	case UART_TX_DONE:
		printf("transmission complete \n");
		break;

	case UART_TX_ABORTED:
		// do something
		break;
		
	case UART_RX_RDY:
		printf("rx rdy \n");
		if((evt->data.rx.len) != 0){
			printf("data received = %s \n", evt->data.rx.buf[evt->data.rx.offset]);
		}


		
		break;

	case UART_RX_BUF_REQUEST:
		printf("requesting buffer \n");
		// do something
		break;

	case UART_RX_BUF_RELEASED:
		printf("buffer released \n");
		// do something
		break;
		
	case UART_RX_DISABLED:
		printf("rx disabled \n");
		uart_rx_enable(dev, rx_buf, sizeof(rx_buf), 100);
		break;

	case UART_RX_STOPPED:
		// do something
		break;
		
	default:
		break;
	}
}


int main(void)
{	

	if (!device_is_ready(uart)) {
    	return;
	}

	int err;
	err = uart_callback_set(uart, uart_cb, NULL);
	if (err) {
		return err;
	}

	uart_rx_enable(uart, rx_buf, sizeof(rx_buf), 100);


	err = uart_tx(uart, tx_buf, sizeof(tx_buf), SYS_FOREVER_US);
	if (err) {
		return err;
	}



	while(1){
		k_msleep(1000);
	}
	return 0;
}

I am having issues understanding how to properly print out all the received data:

I tried to do:

	case UART_RX_RDY:
		printf("rx rdy \n");
		if((evt->data.rx.len) != 0){
			printf("data received = %s \n", evt->data.rx.buf[evt->data.rx.offset]);
		}

		break;

but when I send the data via UART (using Termite) , the following is printed:

I would appreciate if someone could clarify how to correctly print out all the received data.  Thanks in advance

Just for testing, I have also tried to print:

    case UART_RX_RDY:
        printf("rx rdy \n");
        printf("data: %s \n", rx_buf);
        break;

 

and the logs are as following: (captured using Termite):

 

As you can see, it receives the first message (ping) correctly, but after that, the buffer overflows (rx_buf is 10 bytes size) and then it cannot print out the data correctly)

[AHaug]

Hi,

Could you check the solution in the github repo and see if you're able to resolve what is wrong and then let me know if you're still having issues with resolving it and we'll get right back at to find you a solution? 

https://github.com/NordicDeveloperAcademy/ncs-fund 

Kind regards,
Andreas

[zazas321]

The solution in the repository shows how to toggle an LED when a serial message is received but it does not really show how to receive and print a longer serial message. I am interested in being able to receive and parse a longer serial message. For example when I receive messsage "ping", I want to respond with message "pong".

When I send message "toggle_led1" I want to turn ON the LED1 and so on...  In order for this to work I need to be able to receive and learn how to print the full received message.

The solution uses the following method to check what serial data has been received:

if(evt->data.rx.buf[evt->data.rx.offset] == '1')

So I try something simillar just for testing purposes:

	case UART_RX_RDY:
		printf("received message =  %s",evt->data.rx.buf[evt->data.rx.offset]);
		break;

The serial console logs when I send 2 messages (ping and hello):

As you can see from above, it does not work properly

[Achim Kraus]

> it does not seem to show proper values once I change to second dual buffer.

Maybe that's a misinterpretation of UART_RX_BUF_REQUEST and uart_rx_buf_rsp.

From the docu:

Provide pointer to RX buffer, which will be used when current buffer is filled.

It doesn't switch immediately after uart_rx_buf_rsp is called, but when the previous buffer is filled.

[Achim Kraus]

Unfortunately this forum doesn't really allow to answer to a specific comment. My answer was for the comment 2 days ago with the red lines.

[Achim Kraus]

I'm not sure, if the irritation you see is caused by a very short DMA buffer. I would try to use a larger ones. At least in my experience, the async UART works well. I use buffers with 256 bytes.

[zazas321]

This issue is quite complex and it might not be obvious if you dont look at it close enough. The weird behaviour becomes very clear if you try to run the code and use debugger to monitor (evt->data.rx.len, evt->data.rx.offset and both uart buffers uart_double_buffer[0] and uart_double_buffer[1]

[Achim Kraus]

The weird behaviour disappears, if you run my code with larger buffers ;-).

The point is, if you want a "seamless" DMA transfer in time, you need to request the buffers overlapping. I assume, that e.g. the new buffer is usually requested some bytes  ahead (say 32) so that the app provides the new buffer and the DMA still uses the old. When the old is filled, the DMA switches very fast to the already provided new one.

But with 8 bytes, that's not working ;-).

 

[Achim Kraus]

After checking the implementation in uart_nrfx_uart.c my understanding is, that the new buffer is already requested, when the first buffer is initially used or the buffers are actually swapped. Anyway, I guess, using something larger will help.