Help understanding RX / TX

RE: Help understanding RX / TX

Håkon Alseth — Wed, 21 May 2025 07:58:00 GMT

Hi,

Please note that you are toggling pin P0.13, and not P1.13, in your firmware.

Are you certain that you are connecting everything correctly?

In your overlay, you are using GPIO P1, not P0.

Kind regards,

Håkon

RE: Help understanding RX / TX

Boggibill — Wed, 21 May 2025 07:38:04 GMT

Hi Håkon.

I have tried deleting all builds to be on the safe side, but i still have this problem. But the problem still exists, however a different approach works.

This example works:

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


#define UART_DEVICE_NODE DT_NODELABEL(uart1)
static const struct device *const uart_dev = DEVICE_DT_GET(UART_DEVICE_NODE);

#define RX_BUF_SIZE 64


#define TX_PIN 13  // P1.12
#define GPIO_PORT DT_NODELABEL(gpio0)  // Use gpio0 if using P0.x
const struct device *gpio_dev;
#define BAUD_DELAY_US 104

void uart_send_blocking(const char *msg)
{
    while (*msg) {
        uart_poll_out(uart_dev, *msg++);
        k_busy_wait(100); // Slight delay between characters
    }
}

void bitbang_uart_tx_byte(uint8_t byte)
{
    // Start bit (low)
    gpio_pin_set(gpio_dev, TX_PIN, 0);
    k_busy_wait(BAUD_DELAY_US);

    // Send 8 bits, LSB first
    for (int i = 0; i < 8; i++) {
        gpio_pin_set(gpio_dev, TX_PIN, (byte >> i) & 1);
        k_busy_wait(BAUD_DELAY_US);
    }

    // Stop bit (high)
    gpio_pin_set(gpio_dev, TX_PIN, 1);
    k_busy_wait(BAUD_DELAY_US);
}

void uart_receive_for_10_seconds(void)
{
    uint8_t c;
    char rx_buf[RX_BUF_SIZE];
    int rx_pos = 0;

    int64_t start = k_uptime_get();

    while (k_uptime_get() - start < 10000) {
        if (uart_poll_in(uart_dev, &c) == 0) {
            if (rx_pos < RX_BUF_SIZE - 1) {
                rx_buf[rx_pos++] = c;
                if (c == '\n' || c == '\r') {
                    break;
                }
            }
        } else {
            k_msleep(10); // Avoid busy-looping
        }
    }

    if (rx_pos > 0) {
        rx_buf[rx_pos] = '\0';
        printk("Received: %s\n", rx_buf);
    } else {
        printk("No response received within 10 seconds.\n");
    }
}

int main(void)
{
	printk("UART Polling Example Started\n");

    gpio_dev = DEVICE_DT_GET(GPIO_PORT);
    gpio_pin_configure(gpio_dev, TX_PIN, GPIO_OUTPUT);
    gpio_pin_set(gpio_dev, TX_PIN, 1); // Idle high

	while(true) {
		if (!device_is_ready(uart_dev)) {
			printk("UART device not ready\n");
			return 0;
		}
        bitbang_uart_tx_byte('H');
        bitbang_uart_tx_byte('i');
        bitbang_uart_tx_byte('\r');
        bitbang_uart_tx_byte('\n');

		//uart_send_blocking("Hello from nRF52!\r\n");
		printk("Message sent. Waiting for reply...\n");

		uart_receive_for_10_seconds();
		k_msleep(5000); // Avoid busy-looping
	}

    return 0;
}

So why does this work, and not the other one?

Oh, i don't have any good messuring tools, however a voltmeter seems to have a constant voltage (im not sure if that is of any use).

RE: Help understanding RX / TX

Håkon Alseth — Wed, 21 May 2025 07:09:09 GMT

Hi,

When altering device tree, I recommend that you delete/remove the build folder and re-generate it afterwards, to ensure that there's no stale configurations still active.

Did you try probing the lines to see if there's any problems with the voltage level or similar?

Kind regards,

Håkon

RE: Help understanding RX / TX

Boggibill — Tue, 20 May 2025 10:15:33 GMT

Correct, RXD works with both pins, and TXD works on both pins, if i switch between uart0 and uart1 configuration.

But RX and TX does not work at the same time on any configuration.

Meaning the following:

RXD works on pin1.11 with uart1, but TXD does not work with pin1.12 with uart1 setup

RXD works on pin1.12 with uart1, but TXD does not work with pin1.11 with uart1 setup

TXD works on pin1.11 with uart0, but RXD does not work with pin1.12 with uart0 setup

TXD works on pin1.12 with uart0, but RXD does not work with pin1.11 with uart0 setup

So, I could get two ways communication to if i communicate over uart1 and uart0 at the same time, if possible.

RE: Help understanding RX / TX

Håkon Alseth — Tue, 20 May 2025 10:10:04 GMT

Hi,

[quote user="Boggibill"]However reversing the pins yields the same result.[/quote]

you mean that if you use RXD on P1.12, it works, and then switch over to P1.11, and it still works?

Ie. that the failure follows the TXD functionality and not the pin it is configured to?

Kind regards,

Håkon

RE: Help understanding RX / TX

Boggibill — Tue, 20 May 2025 09:55:40 GMT

Hi Håkon.

I have not tested it with a logic analyzer. However reversing the pins yields the same result.

RE: Help understanding RX / TX

Håkon Alseth — Tue, 20 May 2025 09:51:33 GMT

Hi,

[quote user="Boggibill"]

However, now it seems like it is able to transmit and receive on the pins 11, 12.

For some reason using uart1, im able to receive but not transmit.

But my problem is, using uart0 with the following setup, im able to transmit but not receive, the complete oposite.

[/quote]

uart1 is configured to P1.11 and P1.12, can receive, not transmit.

uart0 is configured to P1.11 and P1.12, can transmit, not receive.

Did you check with a logic analyzer to see if there is a problem with the logic levels or similar?

[quote user="Boggibill"]Any logical reason for that?[/quote]

If you reverse the pins, are you then able to receive but not transmit?

Kind regards,

Håkon

RE: Help understanding RX / TX

Boggibill — Tue, 20 May 2025 09:21:54 GMT

Hi.

Thanks, changing pins solved my issues. Atleast partly, the pins I where using where busy doing other things on the board. And thanks for letting me know about the diagram on the back of the boards.

I have a new setup, which is a bit strange.

overlay:

&uart1 {
    status = "okay";
    current-speed = <9600>;
    pinctrl-0 = <&uart1_default>;
    pinctrl-1 = <&uart1_sleep>;
    pinctrl-names = "default", "sleep";
};

&pinctrl {
    uart1_default: uart1_default {
        group1 {
            psels = <NRF_PSEL(UART_TX, 1, 12)>,
                    <NRF_PSEL(UART_RX, 1, 11)>;
            bias-pull-up;
        };
    };

};

main.c:

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

#define MSG_SIZE 32
K_MSGQ_DEFINE(uart_msgq, MSG_SIZE, 10, 4);

static char rx_buf[MSG_SIZE];
static int rx_buf_pos;
static volatile bool uart_tx_done = true;

#define UART_DEVICE_NODE DT_NODELABEL(uart1)
static const struct device *const uart_dev = DEVICE_DT_GET(UART_DEVICE_NODE);

void serial_cb(const struct device *dev, void *user_data)
{
    uint8_t c;
    if (!uart_irq_update(uart_dev) || !uart_irq_rx_ready(uart_dev)) {
		printk("UART IRQ not ready\r\n");
		return;
	}
	printk("UART RX Ready\n");

    while (uart_fifo_read(uart_dev, &c, 1) == 1) {
		printk("RX: %c\n", c);
        if ((c == '\n' || c == '\r') && rx_buf_pos > 0) {
            rx_buf[rx_buf_pos] = '\0';
            k_msgq_put(&uart_msgq, &rx_buf, K_NO_WAIT);
            rx_buf_pos = 0;
        } else if (rx_buf_pos < (sizeof(rx_buf) - 1)) {
            rx_buf[rx_buf_pos++] = c;
        }
    }
}

void print_uart(char *buf)
{
    for (int i = 0; buf[i] != '\0'; i++) {
        uart_poll_out(uart_dev, buf[i]);
        k_busy_wait(100);
    }
}

void send_uart_async(const char *msg)
{
    if (!uart_tx_done) {
        printk("UART busy, skipping TX\n");
        return;
    }

    uart_tx_done = false;
    int ret = uart_tx(uart_dev, msg, strlen(msg), SYS_FOREVER_MS);
    if (ret != 0) {
        printk("uart_tx failed with error: %d\n", ret);
        uart_tx_done = true; // reset flag so we don't block forever
    }
}

int main(void)
{
    printk("UART Echo Started\n");

    if (!device_is_ready(uart_dev)) {
        printk("UART device not ready\n");
        return 0;
    }

    uart_irq_callback_user_data_set(uart_dev, serial_cb, NULL);
    uart_irq_rx_enable(uart_dev);

    print_uart("Hello from echo bot\r\n");
	printk("Hello sent\r\n");

	while(true) {
		print_uart("Hello from nrf52\r\n");
		printk("Sending data to TX\r\n");
		k_sleep(K_SECONDS(1));
    }

    return 0;
}

prj.conf:

CONFIG_SERIAL=y
CONFIG_UART_INTERRUPT_DRIVEN=y
CONFIG_UART_ASYNC_API=y

CONFIG_UART_CONSOLE=n
CONFIG_CONSOLE=n

CONFIG_USE_SEGGER_RTT=y
CONFIG_RTT_CONSOLE=y
CONFIG_LOG=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_PRINTK=y

However, now it seems like it is able to transmit and receive on the pins 11, 12.

For some reason using uart1, im able to receive but not transmit.

But my problem is, using uart0 with the following setup, im able to transmit but not receive, the complete oposite.

&uart0 {
    status = "okay";
    current-speed = <9600>;
    pinctrl-0 = <&uart0_default>;
    pinctrl-1 = <&uart0_sleep>;
    pinctrl-names = "default", "sleep";
};

&pinctrl {
    uart0_default: uart0_default {
        group1 {
            psels = <NRF_PSEL(UART_TX, 1, 12)>,
                    <NRF_PSEL(UART_RX, 1, 11)>;
            bias-pull-up;
        };
    };
};

Any logical reason for that?

RE: Help understanding RX / TX

Håkon Alseth — Tue, 20 May 2025 06:30:02 GMT

Hi,

If you still have issues, please try any unused GPIO pair. flip the kit over, and you can see which pins are already connected on the DK itself.

[quote user="Boggibill"]psels = <NRF_PSEL(UART_TX, 0, 6)>,
<NRF_PSEL(UART_RX, 0, 8)>;[/quote]

Those pins are normally used for uart0. Is uart0 disabled in this case?

Kind regards,

Håkon

RE: Help understanding RX / TX

Boggibill — Tue, 20 May 2025 06:24:37 GMT

Hi.

But this means it should work with P0.06 and P0.08, right?

With this configuration:

pinctrl {
uart1_default: uart1_default {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 6)>,
<NRF_PSEL(UART_RX, 0, 8)>;
};
};

uart1_sleep: uart1_sleep {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 6)>,
<NRF_PSEL(UART_RX, 0, 8)>;
low-power-enable;
};
};
};

And it does not. What am I missing?

RE: Help understanding RX / TX

Håkon Alseth — Mon, 19 May 2025 13:40:28 GMT

Hi,

P0.09 and P0.10 are NFC-pins, and require handling as such, by adding this to the overlay:

&uicr {
	nfct-pins-as-gpios;
};

If you are using the nRF52840-DK, you will also need to adjust some resistors on the board itself:

https://docs.nordicsemi.com/bundle/ug_nrf52840_dk/page/UG/dk/hw_nfc_if.html#d45e110

Kind regards,

Håkon

RE: Help understanding RX / TX

Boggibill — Fri, 16 May 2025 12:16:35 GMT

Oh, and I have also connected P0.09 and P0.10.