UART Transmission Issue

[jdorn]

Hello,

I am trying to develop a set of code that will receive data on uart 1 and transmit that data on uart 2, and vice versa.

I have verified via testing printk's that I am receiving and trying to send all of the correct data.
Uart 2 works correctly, but the transmission from uart 1 only provides the first character that I try to send.

I have made sure that flow control is disabled on both (not even pins are assigned to the flow control pins).

I am using XCTU and USB->UART adapters to communicate with the nrf uarts from my computer.

Here is a screenshot of one of my runs. The order of operations was send on left, send on right, send on right, send on left, send on left

blue sections indicate a sent byte. red indicate a received byte.

It seems like when I try to send multiple times from the right one (which is connected to uart 1), the transmission is blocked after the first byte, and no more can be sent until uart 1 receives data, after which it can send one more byte.

note: i am doing this on a nrf9160dk on the 1.6.1 sdk version. I am using the latest VS Code extensions.

/*
 * Copyright (c) 2020 Nordic Semiconductor ASA
 *
 * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
 */

#include <zephyr.h>
#include <drivers/uart.h>
#include <stdio.h>
#include <string.h>

static uint8_t uart_buf_in[1024];
static uint8_t uart_buf_out[1024];
static uint8_t sendbuf[1024];
static uint8_t recvbuf[1024];
struct device *uart2;
struct device *uart1;
int state;
int outside_data_length;
int esp_data_length;
void uart_cb2(struct device *x);
void uart_cb(struct device *x);

void uart_cb(struct device *x)
{
	uart_irq_update(uart1);

	//receive data from uart 1
	if (uart_irq_rx_ready(uart1)) 
	{
		outside_data_length = uart_fifo_read(uart1, uart_buf_in, sizeof(uart_buf_in));
		uart_buf_in[outside_data_length] = 0;
		strcat (sendbuf, uart_buf_in);
	}
	
	if (outside_data_length > 0)
	{
		outside_data_length = 0; //set to zero for flow control	
		uart_fifo_fill(uart2, sendbuf, strlen(sendbuf));
		strcpy(sendbuf, "");
	}
}
void uart_cb2(struct device *x)
{
	uart_irq_update(uart2);
	
	//receive data from uart2
	if (uart_irq_rx_ready(uart2))
	{
		esp_data_length = uart_fifo_read(uart2, uart_buf_out, sizeof(uart_buf_out));
		uart_buf_out[esp_data_length] = 0;
		strcat(recvbuf, uart_buf_out);
	}

	if (esp_data_length >0)
	{
		esp_data_length = 0;
		uart_fifo_fill(uart1, recvbuf, strlen(recvbuf));
		strcpy(recvbuf, "");
	}
}



void main(void)
{
	//initialize variables
	state = 0;
	outside_data_length = 0;
	esp_data_length = 0;
	strcpy(uart_buf_out, "");
	strcpy(uart_buf_in, "");

	//get uart bindings
	uart2 = device_get_binding("UART_2");
	uart1 = device_get_binding("UART_1");

	//bind uarts to callback functions
	uart_irq_callback_set(uart1, uart_cb);
	uart_irq_callback_set(uart2, uart_cb2);
	
	//enable uart interrupts
	uart_irq_rx_enable(uart1);
	uart_irq_rx_enable(uart2);

	printk("UART loopback start!\n");
	while (1) 
	{	

	}
}

prj.conj only has 3 lines:

CONFIG_ASSERT=y

CONFIG_UART_INTERRUPT_DRIVEN=y

CONFIG_AT_HOST_LIBRARY=n

So in short, I am trying to figure out why my two uart_cb functions behave differently.

[Einar Thorsrud]

Hi,

I am not able to explain this right now. Can you share everything I need to reproduce on my end, so also your device tree overlay, and if there are any other things that are also needed?

[jdorn]

Overlay: just changes pins of uart 1 and uart 2. enables them and sets their speed to 9600.

&uart1 {
	status = "okay";
	current-speed = <9600>;
	tx-pin = <13>;
	rx-pin = <14>;
};

&uart2 {
	status = "okay";
	current-speed = <9600>;
	tx-pin = <15>;
	rx-pin = <16>;
};

&i2c2 {
	status = "disabled";
};

I have two external usb->uart devices (I am using diligent's PmodUSBUART board. I have tested other usb->uart devices and confirmed that it is not a hardware issue).

These usb->uart boards connect between my PC and my DK on UART 1 and UART 2.

I am using the serial console built in to XCTU on the PC  to monitor the uart->usb devices on the PC side.

[jdorn]

Hello,

I have determined that 

uart_fifo_fill(uart2, sendbuf, strlen(sendbuf));

is the offending line of code. for some reason, when I call that function the first time, it succeeds. but the second time (and every time after) it always returns 0 bytes sent and does not transmit any data. note: I have verified that both the buffer is populated and the strlen() function returns the expected value via debugging.

the only way i have found to fix this problem is to receive data on the uart 2 fifo_read function. this resets whatever is blocking the fifo_fill and allows another item to be sent.

note: the other device (uart 1) does not have a similar issue.

[Einar Thorsrud]

Hi,

I have not had a chance to test this but I notice you call uart_fifo_fill() without first calling uart_irq_tx_ready(), and from each others event handlers, and that is not how the API is intended to be used. See the uart_fifo_fill() API documentation.

[jdorn]

I tried that, and using either one of or both tx_ready or tx_enable functions completely prevent me from transmitting messages.

[Einar Thorsrud]

Can you elaborate? Also, you should ensure you call uart_irq_tx_ready() and that it returns 1 before you call uart_fifo_fill().