K3Engraver ACK handling wrong?

[mgmax]

The code for the ACK handling of K3Engraver looks wrong.

I would have expected the following behavior in waitForACK():

• wait until the expected ACK response is received or a timeout occurs
• on timeout, raise an Exception so that the whole lasercutting process stops

The actual code does the following:

In the standard case, waitForACK() waits for 0x09 ("OK") and then returns this value to the caller.
If it does not receive this value after several tries, then it simply returns whatever byte was received last, or 0 if nothing was received at all.

LibLaserCut/src/main/java/de/thomas_oster/liblasercut/drivers/K3EngraverDriver.java

Lines 289 to 303 in c2bee3a

	while (trys < WAIT_FOR_ACK_RETRIES)
	{
	Thread.sleep(WAIT_FOR_ACK_TIME);
	trys++;
	rec = inStream.read(inBuf);
	if (inBuf[0] == (byte) 0x09)
	{
	return rec;
	}
	}
	System.out.println("ACK Timeout");
	return rec;
	}

On timeout, only a warning is printed but the code does not seem to react to the timeout in most cases.

In most cases the return value of waitForACK() is ignored.
In rare cases the code checks for a return value of 1 (not 0x09!) and does something special.

LibLaserCut/src/main/java/de/thomas_oster/liblasercut/drivers/K3EngraverDriver.java

Lines 340 to 347 in c2bee3a

	protected int sendHomeCommand() throws IOException, Exception
	{
	int ret = send4ByteCommand((byte) 0x17);
	if (ret == 1)
	{
	head_abs_pos_x = 0;
	head_abs_pos_y = 0;
	}

I don't have such a lasercutter. Maybe @mariolukas can help?