| 1 | ; Project name : XTIDE Universal BIOS
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| 2 | ; Description : Functions to access BOOTVARS struct.
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| 3 |
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| 4 | ; Section containing code
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| 5 | SECTION .text
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| 6 |
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| 7 | ;--------------------------------------------------------------------
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| 8 | ; Stores POST stack pointer to BOOTVARS.
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| 9 | ;
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| 10 | ; BootVars_StorePostStackPointer
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| 11 | ; Parameters:
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| 12 | ; DS: BDA and Interrupt Vector segment (zero)
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| 13 | ; Returns:
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| 14 | ; Nothing
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| 15 | ; Corrupts registers:
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| 16 | ; AX
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| 17 | ;--------------------------------------------------------------------
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| 18 | ALIGN JUMP_ALIGN
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| 19 | BootVars_StorePostStackPointer:
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| 20 | pop ax ; Pop return address
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| 21 | mov [BOOTVARS.dwPostStack], sp
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| 22 | mov [BOOTVARS.dwPostStack+2], ss
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| 23 | jmp ax
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| 24 |
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| 25 |
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| 26 | ;--------------------------------------------------------------------
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| 27 | ; Initializes stack for boot menu usage.
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| 28 | ; POST stack is not large enough when DPTs are stored to 30:0h.
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| 29 | ;
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| 30 | ; Note regarding LOAD_BDA_SEGMENT_TO: If you force the use of SP
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| 31 | ; then you also have to unconditionally enable the CLI/STI pair.
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| 32 | ; The reason for this is that only some buggy 808x CPU:s need the
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| 33 | ; CLI/STI instruction pair when changing stacks. Other CPU:s disable
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| 34 | ; interrupts automatically when SS is modified for the duration of
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| 35 | ; the immediately following instruction to give time to change SP.
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| 36 | ;
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| 37 | ; BootVars_SwitchToBootMenuStack
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| 38 | ; Parameters:
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| 39 | ; Nothing
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| 40 | ; Returns:
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| 41 | ; SS:SP: Pointer to top of Boot Menu stack
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| 42 | ; Corrupts registers:
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| 43 | ; AX
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| 44 | ;--------------------------------------------------------------------
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| 45 | ALIGN JUMP_ALIGN
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| 46 | BootVars_SwitchToBootMenuStack:
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| 47 | pop ax ; Pop return address
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| 48 | %ifndef USE_186
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| 49 | cli ; Disable interrupts
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| 50 | %endif
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| 51 | LOAD_BDA_SEGMENT_TO ss, sp
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| 52 | mov sp, BOOTVARS.rgbMnuStack ; Load offset to stack
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| 53 | %ifndef USE_186
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| 54 | sti ; Enable interrupts
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| 55 | %endif
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| 56 | jmp ax
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| 57 |
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| 58 |
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| 59 | ;--------------------------------------------------------------------
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| 60 | ; Restores SS and SP to initial boot loader values.
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| 61 | ;
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| 62 | ; Before doing any changes, see the note regarding
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| 63 | ; LOAD_BDA_SEGMENT_TO in BootVars_SwitchToBootMenuStack
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| 64 | ;
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| 65 | ; BootVars_SwitchBackToPostStack
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| 66 | ; Parameters:
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| 67 | ; Nothing
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| 68 | ; Returns:
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| 69 | ; SS:SP: Ptr to POST stack
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| 70 | ; Corrupts registers:
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| 71 | ; AX
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| 72 | ;--------------------------------------------------------------------
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| 73 | ALIGN JUMP_ALIGN
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| 74 | BootVars_SwitchBackToPostStack:
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| 75 | pop ax ; Pop return address
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| 76 | %ifndef USE_186
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| 77 | cli ; Disable interrupts
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| 78 | %endif
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| 79 | LOAD_BDA_SEGMENT_TO ss, sp
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| 80 | %ifndef USE_386
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| 81 | mov sp, [ss:BOOTVARS.dwPostStack]
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| 82 | mov ss, [ss:BOOTVARS.dwPostStack+2]
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| 83 | %else
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| 84 | lss sp, [ss:BOOTVARS.dwPostStack]
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| 85 | %endif
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| 86 | %ifndef USE_186
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| 87 | sti ; Enable interrupts
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| 88 | %endif
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| 89 | jmp ax
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