NetBSD-5.0.2/share/man/man9/man9.i386/bioscall.9

.\"	$NetBSD: bioscall.9,v 1.8 2008/04/30 13:10:59 martin Exp $
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.\" by John Kohl.
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.Dd October 1, 1998
.Dt BIOSCALL 9 i386
.Os
.Sh NAME
.Nm bioscall
.Nd call system BIOS function from real mode
.Sh SYNOPSIS
.In i386/bioscall.h
.Ft void
.Fn bioscall "int function" "struct bioscallregs *regs"
.Sh DESCRIPTION
The
.Nm
function switches the processor into real mode, calls the BIOS interrupt
numbered
.Fa function ,
and returns to protected mode.
.Pp
This function is intended to be called during the initial system
bootstrap when necessary to probe devices or pseudo-devices.
.Pp
The register values specified by
.Fa *regs
(with one exception) are installed before the BIOS interrupt is called.
The processor flags are handled specially.  Only the following flags are
passed to the
BIOS from the registers in
.Fa regs
(the remainder come from the processor's flags register at the time
of the call):
.Ar PSL_C ,
.Ar PSL_PF ,
.Ar PSL_AF ,
.Ar PSL_Z ,
.Ar PSL_N ,
.Ar PSL_D ,
.Ar PSL_V .
.Pp
The
.Va bioscallregs
structure is defined to contain structures for each register, to allow
access to 32-, 16- or 8-bit wide sections of the registers.
Definitions are provided which simplify access to the union members.
.Sh RETURN VALUES
.Nm
fills in
.Fa *regs
with the processor registers as returned from the BIOS call.
.Sh EXAMPLES
The Advanced Power Management driver calls
.Nm
by setting up a register structure with the APM installation check and
device types in registers
.Fa ax
and
.Fa bx ,
then calls the BIOS to fetch the details for calling the APM support
through a protected-mode interface.  The BIOS returns these details in
the registers:
.Pp
.Bd -literal
#include \*[Lt]i386/bioscall.h\*[Gt]
#include \*[Lt]i386/apmvar.h\*[Gt]
struct bioscallregs regs;

regs.AX = APM_BIOS_FN(APM_INSTALLATION_CHECK);
regs.BX = APM_DEV_APM_BIOS;
regs.CX = regs.DX = 0;
regs.ESI = regs.EDI = regs.EFLAGS = 0;
bioscall(APM_SYSTEM_BIOS, \*[Am]regs);
.Ed
.Sh CODE REFERENCES
.Pa sys/arch/i386/i386/bioscall.s ,
.Pa sys/arch/i386/bioscall/biostramp.S
.Sh REFERENCES
.Xr apm 4
.Sh HISTORY
.Nm
first appeared in
.Nx 1.3 .
.Sh BUGS
Not all BIOS functions are safe to call through the trampoline, as they
may depend on system state which has been disturbed or used for other
purposes once the
.Nx
kernel is running.