NAME
bioscall —
call system BIOS function
from real mode
SYNOPSIS
#include <i386/bioscall.h>
void
bioscall(
int
function,
struct
bioscallregs *regs);
DESCRIPTION
The
bioscall() function switches the processor into real mode,
calls the BIOS interrupt numbered
function, and returns
to protected mode.
This function is intended to be called during the initial system bootstrap when
necessary to probe devices or pseudo-devices.
The register values specified by
*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
regs (the remainder come from the
processor's flags register at the time of the call):
PSL_C,
PSL_PF,
PSL_AF,
PSL_Z,
PSL_N,
PSL_D,
PSL_V.
The
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.
RETURN VALUES
The
bioscall() function fills in
*regs
with the processor registers as returned from the BIOS call.
EXAMPLES
The Advanced Power Management driver calls
bioscall() by
setting up a register structure with the APM installation check and device
types in registers
ax and
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:
#include <i386/bioscall.h>
#include <i386/apmvar.h>
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, ®s);
CODE REFERENCES
sys/arch/i386/i386/bioscall.s,
sys/arch/i386/bioscall/biostramp.S
REFERENCES
apm(4)
HISTORY
The
bioscall() function first appeared in
NetBSD 1.3.
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
NetBSD kernel is running.