Change startup code to use kernel's find_first_card

kernel/cards.68k

@@ -2,6 +2,7 @@
 
 | 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
+| Warning to developers: This function must only use PC-relative addressing as it is called from early boot before the kernel is properly mapped.
 find_first_card:
   move.l #0xff0000, a0 | a0 holds the address of the current card
 ffc_loop:

kernel/start.68k

@@ -5,7 +5,7 @@ _start:
 move.l d0, d2 | Move the number of program headers to d2
 move.l a0, a1 | Move the program headaer pointer to a1
 move.b #0x5, d0 | Get the pointer to the MMU card
-bsr.w find_first_card_early
+jsr (find_first_card - 0xC00000)
 cmpa.l #0, a0 | Abort if there is no MMU card
 beq.w no_mmu
 subq.w #0x1, d2 | Adjust the number of program headers for dbra
@@ -13,6 +13,9 @@ phead_loop:
 move.l (a1), d1 | If the type of the program header isn't 1 (LOAD), skip the header
 cmpi.l #0x1, d1
 bne.b next_phead
+move.b (9, a1), d1 | If the segment isn't for the high quarter, skip it
+cmpi.b #0xc0, d1
+bgt.b next_phead
 move.l (20, a1), d4 | Put the memory size in d4
 move.l d4, d3 | Copy the size to d3
 lsr #8, d3 | Shift d3 right 12 bits to get the number of full pages the segment takes up
@@ -23,8 +26,8 @@ beq.b even_page
 addq.l #1, d3
 even_page:
 subq.b #1, d3 | | Adjust the number of pages to map for dbra
-move.l (12, a1), d2 | Get the starting physical page in d3
+move.l (12, a1), d1 | Get the starting physical page in d3
-ori.l #3, d1 | Set the present and writable falgs on the entry
+ori.l #3, d1 | Set the present and writable flags on the entry
 move.l (8, a1), d0 | Get the starting virtual page number in the quarter in d0
 lsr.l #8, d0
 lsr.l #4, d0
@@ -47,32 +50,27 @@ io_map_loop:
 move.l d1, (a1)+ | Write the entry to the mapping page and advance the entry pointer
 addi.l #0x1000, d1 | Advance the entry to the next physical page
 dbra d0, io_map_loop | Loop back if there are more pages to map
+map_done:
 move.l #kernel_map, d0 | Load the pointer to the mapping page into d0
 ori.l #0x1, d0 | Set the map page present flag
 move.l d0, (0x0, a0) | Write the mapping page to both the lower and upper quarter map registers
 move.l d0, (0xC, a0)
-move.w #1, (0x14, a0) | Enable the MMU
+jmp (higher_bridge - 0xC00000) | Jump to the lower-half equivalent of the bridging function
-move.w #0, 0xff0000 | Disable the IO space at the top of the lower 16MB of memory
-move.l #bootstrap_stack, a7 | Load the initial stack pointer
-jmp main | Jump to the kernel's main function
 no_mmu:
 stop #2700 | If there was no MMU card, halt the CPU
 
-| Finds the first card with the type in d0.b, and returns it's IO base address in a0, or 0 if not found
+.text
-| Clobbers d1
+higher_bridge:
-find_first_card_early:
+move.w #1, (0x14, a0) | Enable the MMU
-  move.l #0xff0000, a0 | a0 holds the address of the current card
+jmp in_higher:l | Jump to the higher half (THis function has been called with the PC in the
-ffc_early_loop:
+| lower half, so this seemingly no-op jump instruction actually switches to the higher half)
-  lea (0x100, a0), a0 | Move to the next card
+in_higher:
-  move.b (0xff, a0), d1 | Load the type of the card into d1
+move.w #0, 0xff0000 | Disable the IO space at the top of the lower 16MB of memory
-  beq.b ffc_early_notfound | If the type is 0 (empty slot), we have scanned all cards, so exit the loop
+move.l #0, (0x0, a0) | Disable the mapping in the lower quarter
-  cmp.b d0, d1 | If the card is the type we want, return with the address in a0
+move.l #bootstrap_stack, a7 | Load the initial stack pointer
-  beq.b ffc_early_done
+jmp main | Jump to the kernel's main function
-  bra.b ffc_early_loop | Loop back and check the next card
+
-ffc_early_notfound:
+
-move.l #0x0, a0
-ffc_early_done:
-  rts
 
 .section .early.bss, "aw", @nobits
 kernel_map: