BIOSCALL(9)          NetBSD/i386 Kernel Developer's Manual         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 boot-
     strap 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 reg-
     isters 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 reg-
     ister, to allow access to 32-, 16- or 8-bit wide sections of the regis-
     ters.  Definitions are provided which simplify access to the union mem-
     bers.

RETURN VALUES
     bioscall 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 reg-
     ister structure with the APM installation check and device types in reg-
     isters 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
     bioscall 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.

NetBSD 5.0_STABLE               October 1, 1998              NetBSD 5.0_STABLE
