serial.end() doesn't work

[aster94]

Description:

Serial.end() should free the serial pins and leave the user the ability to do digitalWrite() on them, but it doesn't work. Instead to drive the TX pin to a LOW state i need to reset the board.

I tested the code below with the following cores:

• last stable release from platformio
• master branch
• master + HardwareSerial bugfix & improvement #3713

I also made three logic analyzer captures: la.zip
An example from one of these, as you can see it shows that the pin is driven low only once (after upload of the code or reset)

Sketch:

#include <Arduino.h>

HardwareSerial ser(2);
#define TX_PIN 17

void setup(){}

void loop()
{
    pinMode(TX_PIN, OUTPUT);
    delay(10);

    digitalWrite(TX_PIN, HIGH);
    delay(50);
    digitalWrite(TX_PIN, LOW);
    delay(300);
    digitalWrite(TX_PIN, HIGH);
    delay(50);

    ser.begin(9600);
    delay(10);

    for (uint8_t n = 1; n < 5; n++)
    {
        ser.write(n);
        delay(10);
    }
    ser.end();
    delay(300);
}

NOTE: looks like that the problem was here before #3713 and #3664

[aster94]

@lbernstone do you have any idea about what can cause this behaviour?

[lbernstone]

Turn on verbose debugging so you can see if any errors are shown.
Serial2 is instantiated by default. Why are you not using it?
Make your delays longer- a full second whenever you attach or detach pins.
Try manually detaching after the ser.end:
gpio_matrix_out(TX_PIN, 0x100, false, false);

[lyusupov]

One more ticket related to this issue:
#3563 (comment)

[aster94]

@lbernstone looks like you solved it 😁

At first, I tried as you suggested to put big delays, then slowly I removed all of them and no problem showed up in about 5 minutes running this sketch

#include <Arduino.h>

#define TX_PIN 17

void setup(){}

void loop()
{
    pinMode(TX_PIN, OUTPUT);

    digitalWrite(TX_PIN, HIGH);
    delay(50);
    digitalWrite(TX_PIN, LOW);
    delay(1000);
    digitalWrite(TX_PIN, HIGH);

    Serial2.begin(9600);

    for (uint8_t n = 1; n < 5; n++)
    {
        Serial2.write(n);
        delay(50);
    }
    Serial2.end();
    gpio_matrix_out(TX_PIN, 0x100, false, false);
}

Also, note that after the begin no bytes are lost

I think it is an easy fix if the maintainers need I can make a PR @me-no-dev just tell me if the gpio_matrix_out(TX_PIN, 0x100, false, false); needs a special position in these lines or everywhere would work:

arduino-esp32/cores/esp32/HardwareSerial.cpp

Lines 82 to 89 in 0f77227

	void HardwareSerial::end()
	{
	if(uartGetDebug() == _uart_nr) {
	uartSetDebug(0);
	}
	uartEnd(_uart);
	_uart = 0;
	}

And to make it error-proof I would add _txPin to the protected variables of the HardwareSerial class, and finally add here
_txPin = txPin;

Here the LA log:
log.zip

[lbernstone]

The gpio_matrix disconnect is already buried in the end method. It just isn't working for some reason. I'll see if I can track down where it is dropping the ball.

[marcmathys]

Saw that you are interested in a flutter app to standardize access to BT wearables - did you get anywhere. I also find this interesting and would contribute.

[stale]

[STALE_SET] This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[stale]

[STALE_DEL] This stale issue has been automatically closed. Thank you for your contributions.

[SuGlider]

Issue solved with PR #5385