Remove scan_cards and add find_first_card

scan_cards is unnecessary for the 68k, as it makes more sense to return
the IO base address instead of a card index.

kernel/cards.68k

@@ -1,18 +1,15 @@
-.global scan_cards
+.global find_first_card
 
-scan_cards:
-move.l #(card_types + 255), a0
-move.w #0xFF, d0
-move.l #0xFFFFFF, a1
-1:
-move.b (a1), d1
-move.b d1, (a0)
-lea (-0x100, a1), a1
-lea (-0x1, a0), a0
-dbra d0, 1b
-rts
-
-
-.bss
-card_types:
-.ds.b 256
+| 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

kernel/main.68k

@@ -1,4 +1,3 @@
 .global _start
 _start:
-  bsr.b scan_cards
   stop #0x2700