uart_set_pin() with the same pin for both RX and TX doesn't work! (IDFGH-13954)

[arduino12]

Answers checklist.

• I have read the documentation ESP-IDF Programming Guide and the issue is not addressed there.
• I have updated my IDF branch (master or release) to the latest version and checked that the issue is present there.
• I have searched the issue tracker for a similar issue and not found a similar issue.

IDF version.

v5.3.0

Espressif SoC revision.

ESP32-C3 (revision v0.4)

Operating System used.

Windows

How did you build your project?

VS Code IDE

If you are using Windows, please specify command line type.

PowerShell

Development Kit.

ESP32 C3 Super Mini

Power Supply used.

USB

What is the expected behavior?

Full code demo:

#include "freertos/FreeRTOS.h"
#include "driver/uart.h"
#include "soc/uart_periph.h"
#include "driver/gpio.h"
#include "esp_log.h"


#define BYPASS              (0) // don't use `uart_set_pin`
#define WORKAROUND          (1) // add workaround after calling `uart_set_pin`
#define UART_TX_RX_PIN      (0) // GPIO used for both TX and RX lines - can hook to logic analyzer / USB-UART
#define UART_PORT_NUM       (1)
#define UART_BAUD_RATE      (1000000)
#define UART_BUF_SIZE       (1024)

static const char *TAG = "UART TEST";

void app_main()
{
    uart_config_t uart_config = {
        .baud_rate = UART_BAUD_RATE,
        .data_bits = UART_DATA_8_BITS,
        .parity    = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE,
        .source_clk = UART_SCLK_DEFAULT,
    };

    ESP_ERROR_CHECK(uart_driver_install(UART_PORT_NUM, UART_BUF_SIZE, 0, 0, NULL, 0));
    ESP_ERROR_CHECK(uart_param_config(UART_PORT_NUM, &uart_config));

#if BYPASS
    ESP_ERROR_CHECK(gpio_set_pull_mode(UART_TX_RX_PIN, GPIO_PULLUP_ONLY));
    ESP_ERROR_CHECK(gpio_set_direction(UART_TX_RX_PIN, GPIO_MODE_INPUT_OUTPUT_OD));
    esp_rom_gpio_connect_out_signal(UART_TX_RX_PIN, UART_PERIPH_SIGNAL(UART_PORT_NUM, SOC_UART_TX_PIN_IDX), 0, 0);
    esp_rom_gpio_connect_in_signal(UART_TX_RX_PIN, UART_PERIPH_SIGNAL(UART_PORT_NUM, SOC_UART_RX_PIN_IDX), 0);
#else
    ESP_ERROR_CHECK(uart_set_pin(UART_PORT_NUM, UART_TX_RX_PIN, UART_TX_RX_PIN, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE));
#if WORKAROUND
    esp_rom_gpio_connect_out_signal(UART_TX_RX_PIN, UART_PERIPH_SIGNAL(UART_PORT_NUM, SOC_UART_TX_PIN_IDX), 0, 0);
#endif
#endif

    const char *TX_BUFF = "Test";
    char *rx_buff = (char *)malloc(UART_BUF_SIZE);

    while (1) {
        uart_write_bytes(UART_PORT_NUM, TX_BUFF, sizeof(TX_BUFF));
        int len = uart_read_bytes(UART_PORT_NUM, rx_buff, (UART_BUF_SIZE - 1), 20 / portTICK_PERIOD_MS);
        if (len) {
            rx_buff[len] = '\0';
            ESP_LOGI(TAG, "Echo: %s", rx_buff);
        }
        else {
            ESP_LOGW(TAG, "No echo");
        }
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

I expected:

uart_set_pin(UART_PORT_NUM, UART_TX_RX_PIN, UART_TX_RX_PIN, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE)

to work- but is seems to overwrite the TX output configuration and only the RX pin is configured correctly.

My workaround is to re-write the TX output configuration after the uart_set_pin(..) :

esp_rom_gpio_connect_out_signal(UART_TX_RX_PIN, UART_PERIPH_SIGNAL(UART_PORT_NUM, SOC_UART_TX_PIN_IDX), 0, 0);

I think the uart_set_pin(..) needs to support this case of a single pin for both TX and RX-
(maybe test if rx_pin == tx_pin and if so- apply my workaround?)
I use it to control some single line smart servo motors with open-drain UART bus...

The ESP32 support this common UART configuration (like RS485),
it also support echo-cancellation (may also be nice to have this functionality..)

What is the actual behavior?

When:

#define BYPASS              (0) // don't use `uart_set_pin`
#define WORKAROUND          (0) // add workaround after calling `uart_set_pin`

I get:
W UART TEST: No echo - Bad!

When:

#define BYPASS              (0) // don't use `uart_set_pin`
#define WORKAROUND          (1) // add workaround after calling `uart_set_pin`

or

#define BYPASS              (1) // don't use `uart_set_pin`

I get:
I UART TEST: Echo: Test - Good!

Steps to reproduce.

Compile and run the demo code I made with and without the WORKAROUND..

Debug Logs.

No response

More Information.

No response

[arduino12]

I encountered this bug with MicroPython and opened an issue:
micropython/micropython#16079
(Tested on ESP32-S2, S3, C3)

I finally got here realizing the bug is in uart_set_pin(..)