bioscall - call system BIOS function from real mode
bioscall(int function, struct bioscallregs *regs);
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.
bioscall fills in *regs with the processor registers as returned from the
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:
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 first appeared in NetBSD 1.3.
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.
BSD October 1, 1998 BSD
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