xenia/fox32rom
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New boot mechanism: load sector 0 to 0x800 and execute it

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This commit is contained in:
Ry 2022-10-27 22:42:56 -07:00
parent dafd947987
commit fdf3f8bcf5
2 changed files with 8 additions and 66 deletions
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73
boot.asm
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@ -1,24 +1,15 @@
; disk booting routines
; these are only used during booting, they are not exposed via the jump table
const KERNEL_FILE_STRUCT: 0x01FFF800 ; kernel.bin file struct is right above the system stack
kernel_file_name: data.str "system bin" data.8 0
; read disk 0 and attempt to figure out what type of disk it is, and load the correct binary into memory
; load the boot sector of disk 0 to 0x00000800 and jump to it
; inputs:
; r0: disk size (bytes)
; none
; outputs:
; none (doesn't return)
start_boot_process:
; r0 contains the size of the disk in bytes
; divide the size by 512 and add 1 to get the size in sectors
div r0, 512
inc r0
mov r31, r0
mov r0, BACKGROUND_COLOR
call fill_background
draw_boot_text:
mov r0, boot_str
mov r1, 16
mov r2, 464
@ -29,64 +20,16 @@ draw_boot_text:
mov r12, FOX32ROM_VERSION_PATCH
call draw_format_str_to_background
mov r0, 0 ; sector counter
mov r2, 0x00000800 ; destination pointer
mov r3, 0x80003000 ; command to read a sector from disk 0 into memory
mov r4, 0x80002000 ; command to set the location of the buffer
mov r0, 0x80003000 ; command to read a sector from disk 0 into memory
mov r1, 0x80002000 ; command to set the location of the buffer
; first, check to see if this is a FAT-formatted disk or RYFS-formatted disk
out r4, r2 ; set the memory buffer location
out r3, 0 ; read sector 0 into the buffer
cmp.8 [r2], 0xEB ; check for an x86 jmp instruction, indicating a possible FAT volume
ifz jmp start_boot_process_fat
cmp.8 [r2], 0xE9 ; check for an x86 jmp instruction, indicating a possible FAT volume
ifz jmp start_boot_process_fat
out r3, 1 ; read sector 1 into the buffer
add r2, 2
cmp.16 [r2], 0x5952 ; check for RYFS magic bytes
ifz jmp start_boot_process_ryfs
sub r2, 2
start_boot_process_raw_binary_sector_loop:
out r4, r2 ; set the memory buffer location
out r3, r0 ; read the current sector into memory
inc r0 ; increment sector counter
add r2, 512 ; increment the destination pointer
loop start_boot_process_raw_binary_sector_loop
jmp start_boot_process_done
start_boot_process_fat:
jmp start_boot_process_fat
start_boot_process_ryfs:
; open system.bin
mov r0, kernel_file_name
mov r1, 0
mov r2, KERNEL_FILE_STRUCT
call ryfs_open
cmp r0, 0
ifz jmp start_boot_process_error
; read sector 0 to 0x800
out r1, 0x00000800
out r0, 0
mov r0, KERNEL_FILE_STRUCT
mov r1, 0x00000800
call ryfs_read_whole_file
start_boot_process_done:
; done loading !!!
; now clean up and jump to the loaded binary
call boot_cleanup
jmp 0x00000800
start_boot_process_error:
mov r0, BACKGROUND_COLOR
call fill_background
mov r0, boot_error_str
mov r1, 16
mov r2, 464
mov r3, TEXT_COLOR
mov r4, 0x00000000
mov r10, FOX32ROM_VERSION_MAJOR
mov r11, FOX32ROM_VERSION_MINOR
mov r12, FOX32ROM_VERSION_PATCH
call draw_format_str_to_background
ret
; clean up the system's state before jumping to the loaded binary
; inputs:

1
main.asm
View File

@ -322,7 +322,6 @@ const MENU_FRAMEBUFFER: 0x0215618E ; max 640x480x4 = end address at 0x022821
startup_str: data.str "fox32 - ROM version %u.%u.%u - insert boot disk - F12 for monitor" data.8 0
boot_str: data.str "fox32 - ROM version %u.%u.%u - booting..." data.8 0
boot_error_str: data.str "fox32 - ROM version %u.%u.%u - system.bin not found! - F12 for monitor" data.8 0
menu_items_root:
data.8 1 ; number of menus