[syslinux] Unwanted serial port interaction in pxelinux

[Michael]

I need to do some Windows device driver debugging using WinDbg from a
second system over the serial port.

The system PXE boots into a pxelinux menu first. I have observed that when
the serial port is connected there are characters from the debugging
system that are read and interpreted (as garbage) by pxelinux. Because of
this, I am forced to stop the debugger or unplug the serial cable every
time I reboot the target machine.

I have read about enabling the serial port in syslinux.doc, but nothing
about explicitly disabling this feature.

Target machine is an HP DL360 G2. The BIOS Serial Console setting is
'Disabled'.

Q: Is my BIOS lying to me and sending the COM1 input as keyboard input,
even though it is disabled?

.OR.

Q: Does syslinux/pxelinux read COM1 input by default?

Q: If it is the case that syslinux reads COM1 input, is there a way to
disable this feature?


Thanks in advance,
Michael