[vbox-dev] [PATCH] parport: Allow VMs to change the direction

Bernhard Walle bernhard at bwalle.de
Sun May 22 09:34:16 GMT 2011

If the parport is used as low-level I/O device (like done for simple
logic analyzers or programmer devices for microcontrollers), the host
changes the direction of the parallel port as input and reads the data bits.

Reading has already been implemented, but the direction change was not
forwarded to the ppdev driver on Linux. So what the guest read was not
the state of the hardware but the last value written to the port.

This patch implements changing the direction. The patch has been tested
on Linux host (Arch Linux) with a Linux guest (openSUSE 11.4) with a
simple parport.c file (attached) and with a Windows XP guest (Windows XP
with all patches) with tfla-01.berlios.de and giveio.sys.

Submitted by: Bernhard Walle <bernhard at bwalle.de>
License: MIT License
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