Serial on Linux causes the Arduino to reset

[frankvanbever]

Observed behaviour:

• Whenever the application is started or serial communication is lost using a Linux host the microcontroller is reset.
• There is a discrepancy between the behaviour on Linux and Windows. On Windows the reset is explicityly disabled.

AC:

• The microcontroller is not reset whenever the connection is (re)established.

[frankvanbever]

Ok, it seems that setting DTR (Data Terminal Ready) and RTS (Ready To Send) are set in one fell swoop in the Linux CDC ACM kernel (I'm looking at a different version but the logic should be the same).

static void acm_port_dtr_rts(struct tty_port *port, int raise)
{
	struct acm *acm = container_of(port, struct acm, port);
	int val;
	int res;

	if (raise)
		val = ACM_CTRL_DTR | ACM_CTRL_RTS;
	else
		val = 0;

	/* FIXME: add missing ctrlout locking throughout driver */
	acm->ctrlout = val;

	res = acm_set_control(acm, val);
	if (res && (acm->ctrl_caps & USB_CDC_CAP_LINE))
		dev_err(&acm->control->dev, "failed to set dtr/rts\n");
}

This means that either RTS or DTR can trigger DTR high.

The solution might be as simple as setting SerialPort.RtsEnable to false like the code already does with DTR.

@TomBruyneel if you've got the time can you check this? I'll try to get a .Net development environment set up on my Linux machine but that'll take some time.

[TomBruyneel]

If you want to try the csharp daemon code on linux you will need the following:

• .net core 3.1 sdk
• visual studio code with the c# extension from the marketplace

I'll adjusted the code but don't have a linux machine or arduino to test :)

Still, it seemed to me that even without my code running the arduino was reset as soon as it was plugged in

[TomBruyneel]

A new docker image with the rtsEnable set to false is now available