80 lines
3.2 KiB
Plaintext
80 lines
3.2 KiB
Plaintext
.long fakestack, start
|
|
start:
|
|
move.b #0x1, d0 | Find the ROM card
|
|
bra.b find_first_card
|
|
romfindret:
|
|
move.l a0, a6 | Save the ROM card IO base in a6 for later
|
|
lea (0xF0, a6), a7 | Set up the stack at the end of the ROM's IO space RAM
|
|
bsr.b find_largest_ram | Find the largest RAM card and put the IO base in a5
|
|
move.l a0, a5
|
|
move.l d0, d7
|
|
move.b #0x4, d0 | Find a storage card and put the IO base in a4
|
|
bsr.b find_first_card
|
|
move.l a0, a4
|
|
| Transfer the bootsector load code to the ROM's
|
|
| built in RAM at the start of it's IO space
|
|
move.w #(ramcode_end - ramcode), d0 | Put the length of the ramcode in d0
|
|
move.w #ramcode, a0 | Put the address of the ramcode in a0
|
|
move.l a6, a1 | Put the start of the ROM's IO space RAM in a0
|
|
ramcode_loop:
|
|
move.b (a0)+, (a1)+ | Transfer a byte of ramcode to the ROM's IO space RAM
|
|
dbra d0, ramcode_loop | Loop back if there is more to transfer
|
|
jmp (a6) | Jump to the ramcode
|
|
stop #0x2700
|
|
|
|
ramcode:
|
|
move.b #0x0, (0xFE, a6) | Disable the ROM
|
|
move.l #0x1, (a5) | Enable the RAM at base 0x0
|
|
move.l d7, a7
|
|
| Load sector 0 to 0x0
|
|
move.l #0x0, (a4) | Set the sector number to 0
|
|
| Transfer 0x100 (256) bytes from the storage card's data register to 0x0
|
|
move.w #0x0, a1 | Load a1, the destination address register, with 0x0
|
|
move.w #0xFF, d0 | Load d0 with the sector size - 1.
|
|
sector_loop:
|
|
move.b (4, a4), (a1)+ | Transfer a byte of sector data to the destination
|
|
dbra d0, sector_loop | Loop back if there is more to transfer
|
|
jmp (0x0).W | Jump to the loaded sector
|
|
|
|
stop #0x2700
|
|
ramcode_end:
|
|
|
|
nop | Padding to make sure ramcode_end and find_first_card are different
|
|
|
|
| Finds the first card with the type in d0.b, and returns it's IO base address in a0, or 0 if not found
|
|
| Clobbers d1
|
|
find_first_card:
|
|
move.l #0xff0000, a0 | a0 holds the address of the current card
|
|
ffc_loop:
|
|
lea (0x100,a0), a0 | adda.l #$100,a0 ; Move to the next card
|
|
move.b (0xff, a0), d1 | Load the type of the card into d1
|
|
beq.b ffc_done | If the type is 0 (empty slot), we have scanned all cards, so exit the loop
|
|
cmp.b d0, d1 | If the card is the type we want, return with the address in a0
|
|
beq.b ffc_done
|
|
bra.b ffc_loop | Loop back and check the next card
|
|
ffc_done:
|
|
rts
|
|
|
|
| Finds the largest RAM card, and returns it's IO base address in a0 and size in d0, or 0 if not found
|
|
| Clobbers d1, a1
|
|
find_largest_ram:
|
|
move.l #0x0, d0 | d0 holds the size of the largest RAM card found
|
|
move.w #0x0, a0 | a0 holds the address of the largest RAM card found
|
|
move.l #0xff0000, a1 | a1 holds the address of the current card
|
|
flr_loop:
|
|
lea (0x100,a1), a1 | adda.l #$100,a0 ; Move to the next card
|
|
move.b (0xff, a1), d1 | Load the type of the card into d1
|
|
beq.b flr_done | If the type is 0 (empty slot), we have scanned all cards, so exit the loop
|
|
cmp.b #0x2, d1 | If the card isn't a RAM card, skip it
|
|
bne.b flr_loop
|
|
move.l (0x4, a1), d1 | Load the card's size into d1
|
|
cmp.l d0, d1 | If the current size is less than the largest size found, go back to the start of the loop
|
|
ble.b flr_loop
|
|
move.l d1, d0 | Store the size and address of the new largest card in d0 and a0
|
|
move.l a1, a0
|
|
bra.b flr_loop | Loop back and check the next card
|
|
flr_done:
|
|
rts
|
|
fakestack:
|
|
.long romfindret
|