REALEMU(8) REALEMU(8)
NAME
realemu - software emulation of /dev/realmode
SYNOPSIS
aux/realemu [ -Dpt ] [ -s srvname ] [ -m mountpoint ]
DESCRIPTION
Originally, kernel provided /dev/realmode files with the
arch(3) device to access and call the BIOS.
Interrupts had to be disabled and the processor was switched
in the legacy 16-bit realmode with memory protection dis-
abled to execute BIOS code.
This is problematic in case the BIOS reprograms hardware
currently used by the operating system or when it reenables
interrupts or just crashes. This will freeze or reboot the
machine with no way to recover or diagnose the problem.
To avoid this, realemu is used to emulate the execution of
the BIOS routines by interpreting the machine instructions
and intercepting dangerous actions that would compromise the
systems stability.
Running realemu with no arguments, it mounts itself before
/dev and replaces the original /dev/realmode file in the
current namespace.
Then programs like vga(8) can use it to make their BIOS
calls.
The D flag will enable debug messages for 9P. The p and t
flags control tracing of i/o port access and cpu instruc-
tions to stderr (fd 2).
When a srvname is given with the s argument, the default
mountpoint is ignored and a 9P channel is created in /srv
that can be used to mount the filesystem from another names-
pace. If a mountpoint is given before the srvname argument
then it is ignored, otherwise it will be used.
EXAMPLES
The realemu process is only needed when accessing
/dev/realmode. To invoke a subshell so that realemu exits
normally after aux/vga completes:
% @{rfork n; aux/realemu; aux/vga -m vesa -l $vgasize}
SOURCE
/sys/src/cmd/aux/realemu
Page 1 Plan 9 (printed 12/22/24)
REALEMU(8) REALEMU(8)
SEE ALSO
vga(8), arch(3)
HISTORY
Realemu first appeared in 9front (April, 2011).
Page 2 Plan 9 (printed 12/22/24)