Read bytes from boot drive

diff --git a/Makefile b/Makefile
index 9d95b1ef97134bcebc837fe4ab4cfab1e6fff45a..a85a94acd141033159828870efa184d744d3b681 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 AS = yasm # choose yasm or nasm here
 ASFLAGS = -f bin # compile a raw binary
 
-boot: boot.s print.s
+boot: boot.s print.s disk.s
        $(AS) $(ASFLAGS) -o $@ boot.s
 
 clean:

diff --git a/boot.s b/boot.s
index 51be5d92dd8ee19426be4092d2aaed2c1e96f46d..3a8adc70a9d275e2e17faa53e6772aee0289e36c 100644 (file)
--- a/boot.s
+++ b/boot.s
@@ -2,70 +2,32 @@
        org 7c00h ; boot sector is loaded at 0x7c00
 
 _start
-       mov di, printing_numbers
-       call print
+       mov [boot_drive], dl ; BIOS sets dl to number of boot drive, we don't want to forget this
 
-       or bl, 1
-       mov dx, 0DEADh ; number to print
-       call print_word
-       
-       mov di, space
-       call print
-       
-       xor bl, bl
-       mov dx, 0BEEFh
-       call print_word
-
-       mov di, waiting
-       call print
+       mov bp, 8000h ; Move the stack away
+       mov sp, bp
 
-       mov di, keystroke
-       mov bl, 1
+       push cs
+       pop es
+       mov bx, 9000h ; Load at 0000:9000
+       mov dh, 2 ; Load 5 sectors
+       mov dl, [boot_drive] ; Load from boot drive
+       call read_sectors
 
-.loop
-       mov ah, 0
-       int 16h
-       cmp ah, 1Ch
-       je .enterpressed
-       jmp .continue
-       cmp ah, 0Eh
-       je .backspace
-       jmp .continue
-.enterpressed
-       pusha
-       mov ah, 0Eh
-       mov al, 0Dh
-       int 10h
-       mov al, 0Ah
-       int 10h
-       popa
-       jmp .loop
-.backspace
-       pusha
-       mov ah, 03h
-       mov bh, 0
-       int 10h
-       dec dl
-       mov ah, 02h
-       int 10h
-       mov ah, 0Eh
-       mov al, ' '
-       int 10h
-       mov ah, 02h
-       int 10h
-       popa
-       jmp .loop
-.continue
-       mov [keystroke], al
-       call print
-       jmp .loop
+       mov dx, [9000h] ; Print value at 9000h, should be 0xDEAD
+       call print_word 
+       mov dx, [9000h + 512] ; Print value at 9200h, should be 0xBEEF
+       call print_word
 
-printing_numbers db "Printing some random hex numbers", 0
-waiting db "I await keystrokes", 0
-keystroke db "$", 0
-space db " ", 0
+       jmp $ ; Endless loop
 
 %include "print.s"
+%include "disk.s"
+
+boot_drive resb 1 ; Reserve 1 byte for boot drive number
+
+times 510-($-$$) db 0 ; fill with 0 until 0x1fc is reached
+dw 0AA55h ; BIOS MBR signature
 
-       times 510-($-$$) db 0 ; fill with 0 until 0x1fc is reached
-       dw 0AA55h ; BIOS MBR signature
+times 256 dw 0DEADh ; Fill in 2nd sector with 0xDEAD
+times 256 dw 0BEEFh ; Fill in 3rd sector with 0xBEEF

diff --git a/disk.s b/disk.s
new file mode 100644 (file)
index 0000000..b281c3a
--- /dev/null
+++ b/disk.s
@@ -0,0 +1,39 @@
+; ES:BX - where to load
+; DH - sector count
+; DL - drive number
+
+read_sectors:
+       xor bl, bl
+       mov di, disk_reading
+       call print
+       push dx
+       mov ah, 02h
+       mov al, dh
+       mov ch, 0
+       mov dh, 0
+       mov cl, 2
+       
+       int 13h
+
+       jc read_error
+
+       pop dx
+       cmp dh, al
+       jne read_error
+       ret
+       
+read_error:
+       xor bl, bl
+       mov di, disk_error
+       call print
+       mov dl, ah
+       xor dh, dh
+       call print_word
+       mov dl, al
+       call print_word
+       jmp $
+
+disk_reading db "Reading from disk...", 0
+disk_error db "Failed to read from disk! Take a look at this error code:", 0
+
+       ret