155 lines
5.5 KiB
Plaintext
155 lines
5.5 KiB
Plaintext
STORAGE_SEC equ $0
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STORAGE_CNT equ $4
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STORAGE_CMD equ $8
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STORAGE_DMADR equ $C
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include cards.i
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include string.i
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include memory.i
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section .text,text
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; Initialize the initrd reader
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public initrd_init
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initrd_init:
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move.w #$4, d0 ; Get the pointer to the MMU card
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jsr find_first_card
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move.l a0, storage_card_base
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rts
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; Get the start byte for a specific file in the initrd
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; Pointer to name in a0
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; Number returned in d0, or 0 if not found
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public initrd_find_file
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initrd_find_file:
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movem.l d2/a2, -(a7)
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move.l a0, a2 ; Save the name pointer in a2
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move.l #512, d0 ; Allocate a buffer to read sectors into
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jsr malloc
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move.l a0, a1 ; Save the buffer pointer in a1
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move.l #1, d0 ; Set the first sector to read
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iff_loop:
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movem.l d0/a1, -(a7)
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move.l storage_card_base, a0 ; Read a file header sector
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move.l #1, d1
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bsr.b read_sectors
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movem.l (a7)+, d0/a1
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move.l (a1), d2 ; Abort with a 0 return if we have reached the end of the initrd
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bne.b .1
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move.l #0, d0
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bra.b iff_done
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.1:
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movem.l d0/a1, -(a7)
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move.l a2, a0 ; Compare the passed in file name with the one in the header sector
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adda.l #12, a1
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jsr strcmp
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movem.l (a7)+, d0/a1
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bne.b .2 ; Continue to the next file if the name doesn't match
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addi.l #1, d0 ; Add one to the current sector number to get the start sector of the file
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lsl.l #8, d0 ; Shift the sector number left by 9 to get the start byte of the file
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lsl.l #1, d0
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movem.l (a7)+, d2/a2
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rts
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.2:
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; Add the # of sectors of file data + 1 to the sector number to advance to the next header sector
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addi.l #1, d0
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move.l (4,a1), d2
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add.l d2, d0
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bra.b iff_loop
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iff_done:
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movem.l (a7)+, d2/a2
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rts
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; Reads bytes of a file from the initrd
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; Start byte of file in d0
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; Offset in d1
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; Length in d2
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; Buffer in a0
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public initrd_read_bytes
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initrd_read_bytes:
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add.l d1, d0
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move.l d2, d1
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move.l a0, a1
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move.l storage_card_base, a0
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bra.b read_bytes
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; Reads sectors from a storage card
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; Card base in a0
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; Destination in a1
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; Start sector in d0.l
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; Sector count in d1.l
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read_sectors:
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cmpi.l #0, d1 ; Do nothing if asked to read 0 sectors
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beq.b read_sectors_done
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move.l d0, (STORAGE_SEC,a0) ; Set the sector number
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move.l d1, (STORAGE_CNT,a0) ; Set the sector count
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move.l a1, (STORAGE_DMADR,a0) ; Set the destination address
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move.w #$1, (STORAGE_CMD,a0) ; Issue a DMA read command
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read_sectors_done:
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rts
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; Reads bytes off a storage card
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; Card base in a0
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; Destination in a1
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; Start byte in d0.l
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; Byte count in d1.l
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read_bytes:
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movem.l d2-d5/a2/a3,-(a7) ; Save callee preserved registers
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move.l d0, d4 ; Save start byte in d4
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move.l d1, d5 ; Save byte count in d5
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move.l a1, a3 ; Save destination in a6
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lsr.l #8, d0 ; Divide start byte by 512 to compute starting sector
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lsr.l #1, d0
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move.l d0, d3 ; Save the starting sector in d3
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move.l #1, d1 ; Read the starting sector into the sector buffer
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move.l #sec_buf, a1
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bsr.b read_sectors
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move.l a3, a2 ; Load the destination into a2
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move.l d4, d0 ; Load the start byte into d0
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andi.l #$1FF, d0 ; Modulus start byte by 512 to compute sector data offset
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adda.l d0, a1 ; Add the offset to the start of the sector buffer
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move.l #$200, d1 ; Compute the number of bytes to transfer by subtracting the offset from 512
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sub.l d0, d1
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cmp d5, d1 ; Compare the number of bytes to transfer with the byte count
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ble.b count_ok ; If it was less than the byte count, do not adjust the bytes to transfer
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move.l d5, d1 ; Otherwise, cap the transfer count to the total byte count
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count_ok:
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move.l d1, d4 ; Save the number of bytes in d4
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subi.l #1, d1 ; Subtract 1 from the number of bytes to account for the extra loop done by dbra
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start_sec_loop: ; Transfer the required bytes from the start sector to the destination buffer
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move.b (a1)+, (a2)+
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dbra d1, start_sec_loop
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move.l d3, d0 ; Load the starting sector into d0
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addi #1, d0 ; Compute the start of the middle sectors by adding 1 to the starting sector
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move.l d4, d2 ; Load the number of bytes transferred into d2
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move.l d5, d1 ; Load the byte count into d1
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sub.l d2, d1 ; Compute the number of remaining bytes by subtracting the number of transferred bytes from the byte count
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cmpi.l #0, d1 ; If there are no more bytes to read, end early
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beq.b read_bytes_done
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move.l d1, d4 ; Save the number of remaining bytes in d4
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lsr.l #8, d1 ; Divide remaining bytes by 512 to compute the number of middle sectors
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lsr.l #1, d1
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move.l a2, a1 ; Transfer the sector data to the end of the start sector bytes
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bsr.b read_sectors ; Read the middle sectors
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move.l d1, d3 ; Save the number of middle sectors in d3
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lsl.l #8, d1 ; Multiply the number of middle sectors by 512 to compute the number of bytes transferred
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lsl.l #1, d1
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sub.l d1, d4 ; Subtract the number of transferred bytes from the number of remaining bytes
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cmpi.l #0, d4 ; If there are no more bytes to read, end early
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beq.b read_bytes_done
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adda.l d1, a2 ; Add the number of bytes transferred to a2
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add.l d3, d0 ; Compute the end sector number by adding the start and count of the middle sectors
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move.l #1, d1 ; Set the number of sectors to read to 1
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move.l #sec_buf, a1 ; Set the read address of the sector to the sector buffer
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bsr.w read_sectors ; Read the end sector
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move.l d4, d1 ; Load the number of remaining bytes into d1
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end_sec_loop: ; Transfer the required bytes from the start sector to the destination buffer
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move.b (a1)+, (a2)+
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dbra d1, end_sec_loop
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read_bytes_done:
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movem.l (a7)+, d2-d5/a2/a3 ; Restore callee preserved registers
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rts
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section .bss,bss
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storage_card_base: ds.b 4
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sec_buf: ds.b 512
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