fox32rom: Start implementing RYFS support

boot.asm

@@ -1,6 +1,9 @@
 ; 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 "kernel  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
 ; inputs:
 ; r0: disk size (bytes)
@@ -18,13 +21,18 @@ start_boot_process:
     mov r3, 0x80003000 ; command to read a sector from disk 0 into memory
     mov r4, 0x80002000 ; command to set the location of the buffer
 
-    ; first, check to see if this is a FAT-formatted disk
+    ; 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
@@ -33,7 +41,18 @@ start_boot_process_raw_binary_sector_loop:
     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 kernel.bin
+    mov r0, kernel_file_name
+    mov r1, 0
+    mov r2, KERNEL_FILE_STRUCT
+    mov r3, TEMP_SECTOR_BUF
+    call ryfs_open
+
+    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

disk.asm

@@ -1,5 +1,7 @@
 ; disk routines
 
+const TEMP_SECTOR_BUF: 0x01FFF808
+
 ; read a sector into the specified memory buffer
 ; inputs:
 ; r0: sector number

main.asm

@@ -152,6 +152,7 @@ get_rom_version:
     #include "mouse.asm"
     #include "overlay.asm"
     #include "panic.asm"
+    #include "ryfs.asm"
     #include "vsync.asm"
 
 

ryfs.asm

@@ -0,0 +1,111 @@
+; RYFS routines
+
+; open a file from a RYFS-formatted disk
+; inputs:
+; r0: pointer to file name string (8.3 format, for example "test    txt" for test.txt)
+; r1: disk ID
+; r2: file struct: pointer to a blank 8 byte file struct as described below
+; r3: pointer to sector buffer
+; outputs:
+; r0: first file sector
+;
+; file struct:
+; file_disk: 1 byte
+; file_first_sector: 2 bytes
+; file_seek_offset: 4 bytes
+; file_reserved: 1 byte
+ryfs_open:
+    push r1
+    push r2
+    push r10
+
+    ; r10: pointer to file struct entry
+    mov r10, r2
+    mov.8 [r10], r1 ; write file_disk
+    inc r10
+
+    push r0
+    mov r0, 1
+    mov r2, r3
+    call read_sector
+    pop r0
+
+    ; point to the file name of the first directory entry
+    mov r1, r3
+    add r1, 20
+    mov r2, 11 ; compare 11 bytes
+ryfs_open_find_dir_entry_loop:
+    call compare_memory_bytes
+    ifz jmp ryfs_open_found_dir_entry
+    add r1, 16 ; point to the file name in the next directory entry
+    jmp ryfs_open_find_dir_entry_loop ; FIXME: this never returns if the file wasn't found
+ryfs_open_found_dir_entry:
+    sub r1, 4          ; point to first sector of this file
+    mov.16 [r10], [r1] ; write file_first_sector
+    add r10, 2
+    mov [r10], 0       ; write file_seek_offset
+    inc r10
+    mov.8 [r10], 0     ; write file_reserved
+    movz.16 r0, [r1]
+
+    pop r10
+    pop r2
+    pop r1
+    ret
+
+; read a whole file into the specified buffer
+; FIXME: this will always load a multiple of 506 bytes, even if the file is smaller
+; inputs:
+; r0: pointer to file struct
+; r1: pointer to destination buffer
+; outputs:
+; none
+;
+; file struct:
+; file_disk: 1 byte
+; file_first_sector: 2 bytes
+; file_seek_offset: 4 bytes
+; file_reserved: 1 byte
+ryfs_read_whole_file:
+    push r0
+    push r1
+    push r2
+    push r10
+    push r11
+
+    mov r10, r0
+    mov r11, r1
+
+    ; read the first sector into the temp buffer
+    movz.8 r1, [r0] ; file_disk
+    inc r0
+    movz.16 r0, [r0] ; file_first_sector
+ryfs_read_whole_file_sector_loop:
+    mov r2, TEMP_SECTOR_BUF
+    call read_sector
+
+    ; copy the sector data to the destination buffer
+    mov r0, TEMP_SECTOR_BUF
+    add r0, 6
+    mov r1, r11
+    mov r2, 506
+    call copy_memory_bytes
+
+    ; check to see if this is the last sector
+    ; FIXME: if this is the last sector, it should respect the sector size field in the header
+    sub r0, 4
+    cmp.16 [r0], 0
+    ifz jmp ryfs_read_whole_file_last_sector
+
+    ; there are more sectors left, load them
+    movz.16 r0, [r0] ; sector number
+    mov r1, [r10]    ; file_disk
+    add r11, 506
+    jmp ryfs_read_whole_file_sector_loop
+ryfs_read_whole_file_last_sector:
+    pop r11
+    pop r10
+    pop r2
+    pop r1
+    pop r0
+    ret