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

[AHaug]

Noted!

Thank you for clarifying that the issue was not simply to get the lesson to work. I will have a look at it and return to you when I have something more constructive for you, however that might not be until early next week. 

I hope the delay does not cause too much of a problem for you

Kind regards,
Andreas

[zazas321]

Thats perfectly fine. Thanks :)

[zazas321]

Hello. Maybe you have any feedback regarding this issue? :)

[AHaug]

Hi, 

Apologies for the long response time.

Unfortunately I could not find a simple sample that showcase how to do this, so my best current suggestion is to investigate the peripheral UART and Central uart BLE samples and see how it is done in these samples 

Starting at L129 in peripheral_uarts main.c you can see how the UART_RD_RDY case is handled

case UART_RX_RDY:
		LOG_DBG("UART_RX_RDY");
		buf = CONTAINER_OF(evt->data.rx.buf, struct uart_data_t, data);
		buf->len += evt->data.rx.len;

		if (disable_req) {
			return;
		}

		if ((evt->data.rx.buf[buf->len - 1] == '\n') ||
		    (evt->data.rx.buf[buf->len - 1] == '\r')) {
			disable_req = true;
			uart_rx_disable(uart);
		}

		break;

and bt_receive_cb() L465 peripheral, ble_data_received() L83 in Central_uart should show how the uart messages are handled with regards to writing.

Kind regards,
Andreas

[zazas321]

Hello. I had a look at the zephyr/samples/drivers/uart/echo_bot sample and that sample works exactly how I want it to work. Please look at the serial terminal logs below:

*** Booting Zephyr OS build v3.3.99-ncs1 ***
Hello! I'm your echo bot.
Tell me something and press enter:
hello
Echo: hello
ping
Echo: ping
test
Echo: test
apple
Echo: apple

I can easily echo any message that I send. However this sample uses different UART method (polling) and thats not what I want. I want to be able to echo the whole buffer using ASYNC uart method.

Being able to echo the whole buffer is the most basic requirement for any UART program, it is really hard for me wrap my head around why is this so complicated using the ASYNC method. Would you be able to help any further?. Being able to print a whole received buffer should be as simple as 1 line of code..

I have posted a ticket on zephyr git :

https://github.com/zephyrproject-rtos/zephyr/issues/64115

Perhaps my question is more suited for zephyr instead of here :) 

[AHaug]

Of course the echo_bot sample is what I should've suggested immediately That sample was not on my mind at all this morning! 

But as you state there is a difference in using polling and the async method, and the lesson you started with from the academy course uses Async. Have you attempted to merge the lesson you started with, i.e https://academy.nordicsemi.com/courses/nrf-connect-sdk-fundamentals/lessons/lesson-4-serial-communication-uart/topic/uart-driver/, into the echo_bot?

PS: Unless you've already been recommended by users on the discord to create a ticket on the github, you can also find Zephyrs discord at zephyrproject.org, which might be an even easier way to communicate with other developers using Zephyr

 

Kind regards,
Andreas