Merge pull request #13 from E-Almqvist/dev

Update

src/bios/disk.asm

@@ -1,38 +1,47 @@
 disk_read:
 	pusha
+	push dx ; store dx on stack so that we can compare later
 
-	push dx
-	mov ah, BIOS_DISK_READ 
-	mov al, dh ; sector count 
-	mov cl, 0x02
+	mov ah, BIOS_DISK_READ ; specify function
 
-	mov ch, 0x00 ; read from first cylinder
-	mov dh, 0x00 ; head
+	mov al, dh ; read dh amount of sectors
+	mov ch, 0x00 ; CYLINDER
+	mov dh, 0x00 ; HEAD
+	mov cl, 0x02 ; SECTOR
 
-	; data pointer: es:bx (standard)
-	int BIOS_DISK_INT ; do the interrupt
-	jc read_error ; if flag is set then jump to error
+	int BIOS_DISK_INT ; interrupt
+
+	; Error checks
+	jc read_error ; carry flag set -> error
 
 	pop dx
-	cmp al, dh
+	cmp dh, al ; if dh != al then error
 	jne sector_error
 	
 	popa
-	ret 
+	ret
 
 sector_error:
 	mov bx, sector_error_string
 	call println
 
 read_error:
+	; Inform the user
 	mov bx, read_error_string
 	call println
 
+	; Print the error
+	mov bx, error_code_string
+	call print
+
 	mov dh, ah
 	call print_hex 
 
-disk_loop:
+	mov bx, [ASCII_END]
+	call println
+	
 	jmp $
 
-read_error_string:		db "Disk read error", ASCII_END
-sector_error_string:	db "Invalid number of sectors read", ASCII_END
+read_error_string:		db ASCII_CARRIAGE_RETURN, ASCII_LINEBREAK, "ERROR! Disk read failed.", ASCII_END
+error_code_string:		db "Error code: ", ASCII_END
+sector_error_string:	db "Invalid number of sectors read!", ASCII_END

src/bootloader.asm

@@ -1,51 +1,45 @@
 [org 0x7c00] ; bootsector
+	; Save the boot drive index
+	mov [BOOT_DRIVE], dl
 
-	mov bx, welcome_string		; Print the welcome string
-	call println
+	; Move the stack pointer somewhere safe
+	mov bp, 0x8000 ; move it to 0x8000
+	mov sp, bp
 
-	mov bx, info_string		; Print version info
+	; Print the welcome string
+	mov bx, welcome_string
 	call println
 
-	; Read from disk
-	mov bp, 0x8000
-	mov sp, bp ; move the stack away so that it does not get overwritten
-
-	mov bx, 0x9000
-	mov dh, 2 ; read 2 sectors
-	call disk_read ; read
+	; Read second sector (outside bootsector)
+	mov bx, 0x9000			; LOAD LOCATION 
+	mov dh, 2				; SECTOR-COUNT
+	mov dl, [BOOT_DRIVE]	; DISK-INDEX
+	call disk_read
 
-	mov bx, read_test_string
-	call print
 
+	; Print out whatever bloated data that was read
 	mov dx, [0x9000]
 	call print_hex
 
-	mov bx, byte_sep_string
-	call print
+	mov bx, [ASCII_END]
+	call println
 
-	mov dx, [0x9000 + 512]
+	mov dx, [0x9000 + 512] ; read from second sector too
 	call print_hex
 
-	mov bx, empty_string
-	call println
-
 	jmp $  ; inf loop
 
-; Constants
 %include "equ/ASCII.asm"
-
-; SRs etc
 %include "bios.asm"
 
-welcome_string:		db "e Operating-System (eOS)", ASCII_END
-info_string: 		db "Version 2021 0.0", ASCII_END
-read_test_string:	db "Disk read: ", ASCII_END
-byte_sep_string:	db "; ", ASCII_END
-empty_string:		db ASCII_END
+; Data
+welcome_string:		db "e Operating-System (eOS)", ASCII_CARRIAGE_RETURN, ASCII_LINEBREAK, "Version 2021 0.0", ASCII_END
+BOOT_DRIVE: db 0
 
+; Bootsector
 times 510-($-$$) db 0
-db 0x55, 0xaa ; magic BIOS numbers
+dw 0xaa55 ; magic BIOS numbers
 
-; Bloat bytes to test reading
+; After bootsector 
 times 256 dw 0xEEEE
 times 256 dw 0xAAAA