111 lines
2.8 KiB
Z80 Assembly
111 lines
2.8 KiB
Z80 Assembly
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_start:
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ld sp,0 ; Initialize the stack
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ld a,0x4 ; Find a generic storage card
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call find_first_card
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ld c,0xFF ; Force the top half of the IO address to be the id of the card,
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ld a, b ; so the block transfer instructions can be used
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out (c), a
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; Load the header sectior for the kernel binary to find it's length in sectors
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ld a, 1 ; Set the sector number registers to 1
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ld c, 0
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out (c), a
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inc c
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xor a
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out (c), a
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inc c
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out (c), a
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ld b, a ; Setup a transfer of 256 bytes (1 sector) at a time
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ld c, 0x3 ; from the storage device's data port
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ld h, 0xA0 ; Starting at 0xA000
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ld l, a
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inir
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ld h, 0xA0
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ld l, 0x0
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ld a, (hl)
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add a, 3
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ld c, a
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ld b, 0
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add hl, bc
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ld d, (hl)
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; load the ELF kernel binary off the disk
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ld a, 2 ; Set the sector number registers to 2
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ld c, 0
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out (c), a
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inc c
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xor a
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out (c), a
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inc c
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out (c), a
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ld b, a ; Setup a transfer of 256 bytes (1 sector) at a time
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ld c, 0x3 ; from the storage device's data port
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ld h, 0xA0 ; Starting at 0xA000
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ld l, a
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ld a, d ; Transfer 0x23 times
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loop:
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inir ; Transfer a sector
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dec a
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jp NZ, loop
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ld c,0xFF ; Unforce the top half of the IO address
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in a,(c)
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ld ix, (0xA01C) ; Load IX with the start of the program headers in memory
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ld bc, 0xA000
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add ix, bc
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ld a, (0xA02C) ; load B with the number of program headers
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ld b, a
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phead_loop:
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ld a, (ix+0)
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cp 1
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jp NZ, next_seg
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;Zero out the segemnts place in memory
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push bc
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ld c, (ix+20) ; Load the byte counter with the number of bytes to zero out
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ld b, (ix+21)
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ld e, (ix+8) ; Load the destination & source address register with the destination location of the segment in memory
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ld d, (ix+9)
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ld h, d
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ld l, e
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ld (hl), 0 ; Zero out the firts byte in the segment ( Acts as a 'seed' for the zeroing )
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ldir
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ld c, (ix+16) ; Load the byte counter with the number of bytes to transfer
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ld b, (ix+17)
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ld l, (ix+4) ; Load the source address register with the memory address if the segment data
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ld h, (ix+5)
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ld de, 0xA000
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add hl, de
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ld e, (ix+8) ; Load the destination address register with the destination location of the segment in memory
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ld d, (ix+9)
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ldir; Do the transfer
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pop bc
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next_seg:
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ld de, 32
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add ix, de
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djnz phead_loop
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ld hl, (0xA018) ; Load HL with the program entry point
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jp (hl)
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find_first_card:
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; Finds the first instance of a card type specified in A
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; A is zero if no such card was found, and nonzero if a card was found
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; If a card was found, the ID of the card is returned in B
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; The values in C, D, and E are destroyed
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ld d, a
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ld e, 0x0
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ld bc, 0x01FF ; BC is the IO address to read. B holds the card ID and C which address to read in the card.
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ffc_loop:
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in a, (c) ; Get card type
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cp d ; Check whether the type of the current card is the type we want
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jp Z, done ; If so, return
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cp e ; Check whether the card type is 0 (nonexistent card)
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jp Z, done ; If so, return
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inc b ; Go to the next card
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jp ffc_loop
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done:
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ret
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.if . != 256
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.org 255
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.byte 0
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.endif
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