163 lines
2.7 KiB
Z80 Assembly
163 lines
2.7 KiB
Z80 Assembly
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.global _start
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_start:
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call find_disk
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ld a, 7
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call 0xdffd
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push hl
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ld de, 0
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ld a, 8
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call 0xdffd
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pop hl
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ld (mailbox_num), hl
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msg_loop:
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call yield
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yield_back:
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ld hl, (mailbox_num)
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ld a, 6
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call 0xdffd
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msg_read:
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push bc
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push de
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push hl
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ld b, c
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ld c, 0xB
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call set_frame
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ld a, h
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or 0xB0
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ld h, a
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ld c, (hl)
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inc hl
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ld b, (hl)
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inc hl
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ld e, (hl)
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inc hl
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ld d, (hl)
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ld hl, 0xB000
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jp read_bytes
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ld hl, (0xB004) ; Load destination mailbox into HL
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pop ix
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pop de
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pop bc
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ld a, 5
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call 0xdffd
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halt
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jp msg_loop
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halt
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read_buf: .ds.b 512
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;Given a starting byte number in BC, a byte count in DE, and a destination address in HL, reads those bytes off the disk
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read_bytes:
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ld (start_byte), bc
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ld (byte_count), de
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ld (dest_addr), hl
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ld c, 0
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ld d, 0
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ld e, b
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ld hl, sec_buf
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call read_sector
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ld hl, sec_buf
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ld b, 0 ; Load BC with lower byte of start_byte (sector offset)
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ld a, (start_byte)
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ld c, a
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add hl, bc ; Add the offset to the buffer address
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ld de, (dest_addr)
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ld a, (start_byte) ; A = 255 - offset + 1 (256-offset)
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ld b, a
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ld a, 0xFF
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sub b
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inc a
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ld b, 0 ; Load bc with the value in A
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ld c, a
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ldir
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start_sec_trns_done:
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ld (dest_addr), de
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ld a, (start_byte) ; A = 255 - offset + 1 (256-offset)
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ld b, a
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ld a, 0xFF
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sub b
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inc a
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ld b, 0 ; Load bc with the value in A
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ld c, a
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ld hl, (byte_count)
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scf
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ccf
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sbc hl, bc
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ld (rem_bytes), hl
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ld b, h
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ld c, 0
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ld d, 0
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ld a, (start_byte+1)
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inc a
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ld e, a
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ld hl, (dest_addr)
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sector_loop:
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push bc
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call read_sector
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inc de
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pop bc
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djnz sector_loop
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ld (dest_addr), hl
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ld hl, (sec_buf)
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call read_sector
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ld hl, (sec_buf)
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ld de, (dest_addr)
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ld b, 0
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ld a, (rem_bytes)
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ld c, a
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ldir
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read_bytes_done:
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ret
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start_byte: .ds.b 2
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byte_count: .ds.b 2
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dest_addr: .ds.b 2
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rem_bytes: .ds.b 2
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sec_buf: .ds.b 256
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; Given a sector number in C:DE and a buffer address in HL, reads the sector off disk.
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; Clobbers A, BC, HL
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read_sector:
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push bc
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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, (disk_num) ; so the block transfer instructions can be used
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out (c), a
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pop bc
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ld a, c
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ld c, 0
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out (c), e
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inc c
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out (c), d
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inc c
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out (c), a
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ld b, 0x0 ; 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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inir
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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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read_sec_done:
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ret
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.global find_disk
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; Clobbers A and HL
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find_disk:
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ld b,0x4
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call find_first_card
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ld a, l
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ld (disk_num), a
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ret
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disk_num: .ds.b 1
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mailbox_num: .ds.b 2
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/* Start sector: Start byte / 256 */
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/* Offset in start sector: Start byte % 256 */
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/* Rem bytes: Byte count - (256 - Offset in start sector) */
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/* Middle sectors start: start sector + 1 */
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/* Middle sectors count: Rem bytes / 256 */
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/* End sector: Middle sectors start + Middle sectors count */
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/* End sector copy length: Rem bytes % 256 */
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