source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Inc/BootVars.inc@ 366

; Project name  :   XTIDE Universal BIOS
; Description   :   Defines for BOOTVARS struct used by boot menu
;                   and drive initialization.
%ifndef BOOTVARS_INC
%define BOOTVARS_INC


BOOT_READ_RETRY_TIMES       EQU     3



; Pre-boot variables. These do not exist after successful boot to OS.
; Segment is always 0000h, same as BDA segment
struc BOOTVARS
                    resb    7C00h
    .rgbAtaInfo:                    ; 7C00h, ATA Information for drive detection
    .rgbBootSect    resb    512     ; 7C00h, Boot sector
                    resb    256     ; Boot Menu stack
    .rgbMnuStack:
    .dwPostStack    resb    4       ; POST stack pointer when entering INT 19h
    .wMagicWord     resb    2       ; I wish we didn't need this
    .rgBootNfo:                     ; Array containing BOOTNFO structs
endstruc

; Magic WORD to detect when BOOTVARS is available.
BOOTVARS_MAGIC_WORD         EQU     1110011001100111b



;--------------------------------------------------------------------
; Stores POST stack pointer to BOOTVARS.
;
; STORE_POST_STACK_POINTER
;   Parameters:
;       ES:     BDA and Interrupt Vector segment (zero)
;   Returns:
;       Nothing
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
%macro STORE_POST_STACK_POINTER 0
    mov     [es:BOOTVARS.dwPostStack], sp
    mov     [es:BOOTVARS.dwPostStack+2], ss
%endmacro


;--------------------------------------------------------------------
; Initializes stack for boot menu usage.
; POST stack is not large enough when DPTs are stored to 30:0h.
;
; Note regarding LOAD_BDA_SEGMENT_TO: If you force the use of SP
; then you also have to unconditionally enable the CLI/STI pair.
; The reason for this is that only some buggy 808x CPU:s need the
; CLI/STI instruction pair when changing stacks. Other CPU:s disable
; interrupts automatically when SS is modified for the duration of
; the immediately following instruction to give time to change SP.
;
; SWITCH_TO_BOOT_MENU_STACK
;   Parameters:
;       Nothing
;   Returns:
;       SS:SP:  Pointer to top of Boot Menu stack
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
%macro SWITCH_TO_BOOT_MENU_STACK 0
%ifndef USE_186
    cli                                 ; Disable interrupts
%endif
    LOAD_BDA_SEGMENT_TO ss, sp
    mov     sp, BOOTVARS.rgbMnuStack    ; Load offset to stack
%ifndef USE_186
    sti                                 ; Enable interrupts
%endif
%endmacro


;--------------------------------------------------------------------
; Restores SS and SP to initial boot loader values.
;
; Note! Must return with AX=0 and CF preserved.
; See Int19hMenu_JumpToBootSector_or_RomBoot.
;
; SWITCH_BACK_TO_POST_STACK
;   Parameters:
;       AX:     BDA and Interrupt Vector segment (zero)
;   Returns:
;       SS:SP:  Ptr to POST stack
;   Corrupts registers:
;       Nothing (not even FLAGS)
;--------------------------------------------------------------------
%macro SWITCH_BACK_TO_POST_STACK 0
%ifndef USE_386
    cli
    mov     ss, ax
    mov     sp, [ss:BOOTVARS.dwPostStack]
    mov     ss, [ss:BOOTVARS.dwPostStack+2]
    sti
%else
    mov     ss, ax
    lss     sp, [ss:BOOTVARS.dwPostStack]
%endif
%endmacro


%endif ; BOOTVARS_INC