UART isue

[Vitaliy Freidovich]

Hi,

I experience a very strange issue with UART.

When I try to send data via /dev/ttyACM0 device it looks like the characters sent are buffered and sent only upon the following transmission,

and in some circumstances the first character gets overwritten.

For instance, using minicom, when I type-in: 1234,
The following output is printed: 

in uart_irq_handler!                                                            
RX is ready!                                                                    
value: ~                                                                        
in uart_irq_handler!                                                            
RX is ready!                                                                    
value: 1                                                                          
in uart_irq_handler!                                                            
RX is ready!                                                                    
value: 2                                                                          
in uart_irq_handler!                                                            
RX is ready!                                                                    
value: 3      

trying afterwards: echo -en "1,abc" > /dev/ttyACM0

I get:

in uart_irq_handler!                                                            
RX is ready!                                                                    
value: 4                                                                        
value: ,                                                                        
value: a                                                                        
value: b                                                                        
value: c                                                                        
in uart_irq_handler!                                                            
RX is not ready! 

Details about my environment:

• nrf52833DK
• nRF Connect SDK 1.7.1
• minicom is configured with 115200, 8N1, Hardware & Software flow control Np
• I have modified the nrf25833,dtsi file to contain the following uart&lpuart sections:

• uart1: uart@40028000 {
  	        compatible = "nordic,nrf-uarte";
  	        current-speed = <115200>;
  	        reg = <0x40028000 0x1000>;
  	        interrupts = <40 5>;
  	        label = "UART_1";
  	        status = "okay";
  	        /delete-property/ rts-pin;
  	        /delete-property/ cts-pin;
  	        /delete-property/ hw-flow-control;
  
  	        lpuart: nrf-sw-lpuart {
  	                compatible = "nordic,nrf-sw-lpuart";
  	                status = "okay";
  	                label = "LPUART";
  	                req-pin = <46>;
  	                rdy-pin = <47>;
  	        };
  		};

Source code:

#include <zephyr.h>
#include <zephyr/types.h>
#include <sys/printk.h>
#include <drivers/uart.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

static void uart_irq_handler(const struct device *lpuart_device, void *context)
{
    int result;

    printk("in uart_irq_handler!\n");
    result = uart_irq_update(lpuart_device);
    if (result != 1) {
        printk("uart_irq_update failed, with error: %d\n", result);
        return ;
    }

	if (uart_irq_rx_ready(lpuart_device)) {
		uint8_t buffer[100];
        char command[100];
		int length;
        printk("RX is ready!\n", result);
		do {
            length = uart_fifo_read(lpuart_device, buffer, sizeof(buffer));
            if (length > 0) {
                sprintf(command, "%c", buffer[0]);
                printk("value: %s\n",command);
                buffer[0] = '-1';
            }
		} while (length > 0) ;
	} else {
         printk("RX is not ready!\n", result);
         uart_irq_update(lpuart_device);
    }
}


void start_uart(void) {

    const struct device *lpuart_device;
    uint8_t buffer[1];

    printk("in start_uart\n");
	lpuart_device = device_get_binding("UART_0");
	if (lpuart_device == NULL) {
        printk("Error! CANNOT get low power UART device!\n");
        return ;
    }
	uart_irq_callback_set(lpuart_device, uart_irq_handler);
	uart_irq_rx_enable(lpuart_device);
    printk("in start_uart, successfully set UART IRQ\n");
}

[Krzysztof Chruscinski]

Hi,

lpuart can only be used with another instance of lpuart on the other side. It implements 2 pin control protocol which replaces CTS/RTS and allows receiver to go to sleep in idle.

You need standard UART with or without flow control in that case.

[Vitaliy Freidovich]

Thanks for your response. I understand from the documentation here https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/drivers/uart_nrf_sw_lpuart.html that LPUART supersedes regular UART, and provides the same communication API & protocol above the HW level.

If this is not the case, can you please point me to documentation regarding using regular UART in the nRF Connect SDK? 
I have not found any reference to regular UART and thought that LPUART is the way to implement UART now.
I'm not using nRF5 SDK so libuarte and the similar will not work for me.

Thanks!

[Vitaliy Freidovich]

I tried picocom with the same parameters, no change in results

How would you advise to proceed?

[Vitaliy Freidovich]

Hi,

Any thoughts on this one?

How would you recommend to proceed?

Thanks!

[Hakon]

I can try to reproduce the issue with an nrf52833 DK. Can you include the entire project here including prj.conf and overlays?

[Vitaliy Freidovich]

Sure!

Here's the source code:
.

#include <zephyr.h>
#include <device.h>
#include <drivers/uart.h>

#include <string.h>

/* change this to any other UART peripheral if desired */
#define UART_DEVICE_NODE DT_CHOSEN(zephyr_shell_uart)

#define MSG_SIZE 32

/* queue to store up to 10 messages (aligned to 4-byte boundary) */
K_MSGQ_DEFINE(uart_msgq, MSG_SIZE, 10, 4);

static const struct device *uart_dev = DEVICE_DT_GET(UART_DEVICE_NODE);

/* receive buffer used in UART ISR callback */
static char rx_buf[MSG_SIZE];
static int rx_buf_pos;

/*
 * Read characters from UART until line end is detected. Afterwards push the
 * data to the message queue.
 */
void serial_cb(const struct device *dev, void *user_data)
{
	uint8_t c;

	if (!uart_irq_update(uart_dev)) {
		return;
	}

	while (uart_irq_rx_ready(uart_dev)) {

		uart_fifo_read(uart_dev, &c, 1);

		if ((c == '\n' || c == '\r') && rx_buf_pos > 0) {
			/* terminate string */
			rx_buf[rx_buf_pos] = '\0';

			/* if queue is full, message is silently dropped */
			k_msgq_put(&uart_msgq, &rx_buf, K_NO_WAIT);

			/* reset the buffer (it was copied to the msgq) */
			rx_buf_pos = 0;
		} else if (rx_buf_pos < (sizeof(rx_buf) - 1)) {
			rx_buf[rx_buf_pos++] = c;
		}
		/* else: characters beyond buffer size are dropped */
	}
}

/*
 * Print a null-terminated string character by character to the UART interface
 */
void print_uart(char *buf)
{
	int msg_len = strlen(buf);

	for (int i = 0; i < msg_len; i++) {
		uart_poll_out(uart_dev, buf[i]);
	}
}

void main(void)
{
	char tx_buf[MSG_SIZE];

	if (!device_is_ready(uart_dev)) {
		printk("UART device not found!");
		return;
	}

	/* configure interrupt and callback to receive data */
	uart_irq_callback_user_data_set(uart_dev, serial_cb, NULL);
	uart_irq_rx_enable(uart_dev);

	print_uart("Hello! I'm your echo bot.\r\n");
	print_uart("Tell me something and press enter:\r\n");

	/* indefinitely wait for input from the user */
	while (k_msgq_get(&uart_msgq, &tx_buf, K_FOREVER) == 0) {
		print_uart("Echo: ");
		print_uart(tx_buf);
		print_uart("\r\n");
	}
}

prj.conf:

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=4096

# BT configuration 
CONFIG_BT=y
CONFIG_BT_DEBUG_LOG=y
CONFIG_BT_SMP=y
CONFIG_BT_SIGNING=y
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_DIS=n
CONFIG_BT_ATT_PREPARE_COUNT=5
CONFIG_BT_BAS=n
CONFIG_BT_HRS=n
CONFIG_BT_PRIVACY=y
CONFIG_BT_DEVICE_NAME="AAA"
CONFIG_BT_DEVICE_APPEARANCE=833
CONFIG_BT_DEVICE_NAME_DYNAMIC=y
CONFIG_BT_DEVICE_NAME_MAX=128
CONFIG_BT_KEYS_OVERWRITE_OLDEST=y
CONFIG_BT_SETTINGS=y
CONFIG_BT_L2CAP_TX_MTU=252
CONFIG_BT_BUF_ACL_RX_SIZE=256

CONFIG_FLASH=y
CONFIG_FLASH_PAGE_LAYOUT=y
CONFIG_FLASH_MAP=y
CONFIG_NVS=y
CONFIG_SETTINGS=y

CONFIG_PRINTK=y
CONFIG_LOG_PRINTK=y
CONFIG_LOG=y
CONFIG_LOG_MODE_IMMEDIATE=y
CONFIG_LOG_MAX_LEVEL=4
CONFIG_USE_SEGGER_RTT=y
CONFIG_RTT_CONSOLE=y
CONFIG_UART_CONSOLE=y

CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_SECURE_BOOT=y
CONFIG_MCUMGR=y
CONFIG_MCUMGR_CMD_OS_MGMT=y
CONFIG_MCUMGR_CMD_IMG_MGMT=y
CONFIG_MCUMGR_SMP_BT=y
CONFIG_MCUMGR_SMP_BT_AUTHEN=n

CONFIG_IMG_MANAGER=y

CONFIG_NRFX_TEMP=y

CONFIG_SERIAL=y
CONFIG_UART_INTERRUPT_DRIVEN=y
CONFIG_UART_USE_RUNTIME_CONFIGURE=y
CONFIG_USB_CDC_ACM=n

rv32m1_vega_ri5cy.overlay:

/*
 * Copyright 2019 NXP
 *
 * SPDX-License-Identifier: Apache-2.0
 */

&lptmr1 {
	interrupt-parent = <&intmux0_ch2>;
};

&intmux0_ch2 {
	status = "okay";
};

&intmux0_ch3 {
	status = "okay";
};

&generic_fsk {
	interrupt-parent = <&intmux0_ch3>;
	status = "okay";
};

Please let me know how it behaves for you and what you see.

Thanks!

[Hakon]

Thank you, I'll have a look.