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I am trying to implement APM to my OS. While I can enable APM in real mode (using int 0x15), how I can switch power states in protected mode? I need to jump to real mode or vm86 mode? I readed the documentation and I got more confused

This interface allows a protected mode APM Driver to invoke the APM BIOS functions without the need to first switch into real or virtual-86 mode.

So, how can I call the 0x15 interrupt (to use the APM functions) if I'm in protected mode? I can't do that!

I know that APM is kinda obsolete, but ACPI is too overcomplicated, I just want things simple for now.

btw, here is my code so far:

extern print_string
global set_power_stateoff

enableAPM:
    ; Installation check
    mov ah, 0x53
    mov al, 0x00
    xor bx, bx
    int 0x15
    jc .error
    ; Conecting to protected mode APM interface
    mov ah, 0x53
    mov al, [0x3]
    xor bx, bx
    int 0x15
    jc .error
    ; Enabling power mngm. for all devices
    mov al, 0x53
    mov ah, 0x08
    mov bx, 0001h
    mov cx, 0001h
    int 0x15
    jc .error ; if carry = 1, we have an error
    .error:
    mov si, apmerrno
    call print_string
    ret

set_power_stateoff:
    ; All devices off
    mov ah, 0x53
    mov al, 0x07
    mov bx, 0x0001
    mov cx, [0x0003]
    int 0x15

section .data:
apmerrno: db "APM interface not supported! :(", 0x0A, 0x0D, 0

EDIT: I discovered that something called "BIOS32", which is used to call BIOS interrupts from protected mode. It can be used for APM procmode call?

1 Answers1

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As far as I know; the "int 0x15, ax=0x5303" BIOS function returns information that you need to use to set up three consecutive descriptors (e.g. in your GDT) plus the offset in one of those areas for the 32-bit entry point. After you've created the descriptors you'd call the specified entry point in the code segment that the first descriptor you created describes (e.g. with call far dword [ ..]) and it'd behave the same as "int 0x15" would have in real mode (with same input and output parameters in the same registers, etc).

Note: For the code you've posted, the mov al, [0x3] is a bug and should be mov al,0x03 (but I'd combine it with the previous instruction - e.g. mov ax,(0x53 << 8) | 0x03).

Brendan
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  • The official spec has the title "`Advanced Power Management (APM) BIOS Interface Specification`" . You should be able to cut&paste the spec's title into a search engine and find Revision 1.2 (from 1996), which includes a description of everything (e.g. functions and their input/output parameters) and some appendixes (e.g. "Appendix D - APM Driver Considerations") – Brendan Feb 13 '19 at 06:24