BIOSCALL(9)

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, &regs);

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.