4fc5324f2a
Instead of accessing one byte at a time, use a DMA-like system to read/write a whole sector at a time directly to/from memory.
57 lines
1.9 KiB
NASM
57 lines
1.9 KiB
NASM
; disk booting routines
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; these are only used during booting, they are not exposed via the jump table
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; read disk 0 and attempt to figure out what type of disk it is, and load the correct binary into memory
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; inputs:
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; r0: disk size (bytes)
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; outputs:
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; none (doesn't return)
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start_boot_process:
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; r0 contains the size of the disk in bytes
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; divide the size by 512 and add 1 to get the size in sectors
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div r0, 512
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inc r0
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mov r31, r0
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mov r0, 0 ; sector counter
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mov r2, 0x00000800 ; destination pointer
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mov r3, 0x80003000 ; command to read a sector from disk 0 into memory
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mov r4, 0x80002000 ; command to set the location of the buffer
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; first, check to see if this is a FAT-formatted disk
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out r4, r2 ; set the memory buffer location
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out r3, 0 ; read sector 0 into the buffer
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cmp.8 [r2], 0xEB ; check for an x86 jmp instruction, indicating a possible FAT volume
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ifz jmp start_boot_process_fat
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cmp.8 [r2], 0xE9 ; check for an x86 jmp instruction, indicating a possible FAT volume
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ifz jmp start_boot_process_fat
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start_boot_process_raw_binary_sector_loop:
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out r4, r2 ; set the memory buffer location
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out r3, r0 ; read the current sector into memory
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inc r0 ; increment sector counter
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add r2, 512 ; increment the destination pointer
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loop start_boot_process_raw_binary_sector_loop
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jmp start_boot_process_done
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start_boot_process_fat:
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;
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start_boot_process_done:
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; done loading !!!
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; now clean up and jump to the loaded binary
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call boot_cleanup
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jmp 0x00000800
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; clean up the system's state before jumping to the loaded binary
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; inputs:
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; none
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; outputs:
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; none
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boot_cleanup:
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; clear the background
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mov r0, BACKGROUND_COLOR
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call fill_background
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; disable the menu bar
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mov r0, 0x8000031E
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out r0, 0
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ret |