Updated build script for new bootloader.

Author: kevinsa5

boot_sect2.asm

@@ -3,9 +3,10 @@
 ; Written March 28, 2014
 ;==================================
 
-	ORG 0x7C00
-	jmp 0x0000:start
+	ORG 0x7E00
+    jmp 0x0000:start
 
+    ;BIOS_DATA_AREA equ 0x400 
 	KERNEL_ADDRESS equ 0x200
 	NUM_SECTORS equ 57
 
@@ -18,7 +19,7 @@
 		dw 0xffff		; Limit (bits 0-15)
 		dw 0x0			; Base (bits 0-15)
 		db 0x0			; Base (bits 16-23)
-		db 10011010b		; 1st flags, type flags
+		db 10011010b		; 1st flags, access byte
 		db 11001111b		; 2nd flags, Limit (bits 16-19)
 		db 0x0			; Base (bits 24-31)
 	gdt_data:
@@ -46,7 +47,7 @@
 ; Set up the stack:
 
 	cli
-	mov bp, 0x9000
+	mov bp, 0x7C00
 	mov sp, bp
 	mov ss, ax
 	sti
@@ -55,36 +56,52 @@
 
 	mov [BOOT_DRIVE], dl
 
-; Print out messages
+; Detect Low Memory (below 1Mb, usually below 640Kb)
 
-	mov bx, MSG_1
-	call println
-	mov bx, MSG_2
-	call println
+    xor ax, ax
+    int 0x12
+    jc .mem_error
+    ; ax now contains the # of kB from zero of continuous memory
+    mov bx, ax
+    call printint
+    mov bx, MSG_KB
+    call println
+    jmp .wait
 
-; Wait for keystroke
+.mem_error:
+    jmp $
 
+; Wait for keystroke
+.wait:
+	mov bx, MSG_2
+	call println
 	mov ah, 0
 	int 0x16
 
 ; Load the kernel
 
-	mov bx, MSG_3
+	mov bx, MSG_READING
+	call print
+	mov bx, NUM_SECTORS
+	call printint
+	mov bx, MSG_FROMDISK
 	call println
 
 	mov bx, KERNEL_ADDRESS
 	mov dh, NUM_SECTORS 
 	mov dl, [BOOT_DRIVE]
 	
 ; load DH sectors to ES:BX from drive DL
-
+; Add a looping thing here to load one sector at a time, rather than all at once
 	push dx
 	mov ah, 0x02		; 0x13 read sector
-	mov al, dh
+;.load_loop:
+	mov al, dh		; how many sectors to read
 	mov ch, 0		; cylinder 0
 	mov dh, 0		; head 0
-	mov cl, 2		; start at sector 2 (1 is boot sector)
+	mov cl, 3		; start at sector 2 (1 is boot sector)
 	int 0x13
+	
 	jc .disk_error
 	pop dx
 	cmp dh, al
@@ -99,7 +116,13 @@
 	call println
 	call halt
 .incomplete:
-	mov bx, INCOMPLETE_READ
+	mov bx, DISK_ERROR
+	call println
+	mov bx, MSG_READ
+	call print
+	mov bl, dh
+	call printint
+	mov bx, MSG_FROMDISK
 	call println
 	call halt
 
@@ -113,6 +136,10 @@ enter_pm:
 	mov eax, cr0
 	or eax, 0x1
 	mov cr0, eax
+
+    ; flush the prefetch input queue
+    ; Perform far jump to selector 08h (offset into GDT, pointing at a 32bit PM code segment descriptor) 
+    ; to load CS with proper PM32 descriptor)
 	jmp CODE_SEG:init_pm	; flushes real-mode commands
 
 [BITS 32]
@@ -127,7 +154,8 @@ init_pm:
 	mov esp, ebp
 	mov ebx, MSG_5
 	call printpm
-	call KERNEL_ADDRESS
+
+	jmp KERNEL_ADDRESS
 	jmp $
 	
 	
@@ -137,32 +165,63 @@ init_pm:
 ; string address in bx
 [BITS 16]
 println:
+	call print
+	mov al, 0x0D		; LF CR
+	int 0x10
+	mov al, 0x0A
+	int 0x10
+	ret
+
+print:
 	mov ah, 0x0e		; int 0x10 teletype output
-.println_repeat:	
+.print_repeat:	
 	mov al, [bx]
 	cmp al, 0
-	je .println_done
+	je .print_done
 	int 0x10
 	inc bx
-	jmp .println_repeat
-.println_done:
-	mov al, 0x0D		; LF CR
-	int 0x10
-	mov al, 0x0A
-	int 0x10
+	jmp .print_repeat
+.print_done:
 	ret
 
 halt:
 	mov bx, HALTING
 	call println
 	jmp $
 
+; int in bx, must be 000 - 999
+printint:
+	push dx
+	push bx
+	push ax
+	xor dx, dx
+	mov ax, bx
+	mov bx, 100
+	div bx		;divide dx:ax by bx, store in ax, remainder in dx
+	mov [NUM_BUFFER], al
+	add [NUM_BUFFER], byte '0'
+	mov ax, dx
+	xor dx, dx
+	mov bx, 10
+	div bx
+	mov [NUM_BUFFER+1], al
+	add [NUM_BUFFER+1], byte '0'
+	mov [NUM_BUFFER+2], dx
+	add [NUM_BUFFER+2], byte '0'
+	mov bx, NUM_BUFFER
+	call print
+	pop ax
+	pop bx
+	pop dx
+    ret
+
 [BITS 32]
 printpm:
 	VIDEO_MEM equ 0xb8000
 	WHITE_ON_BLACK equ 0x0f
 	pusha
 	mov edx, VIDEO_MEM
+	add edx, 160*20
 .repeat:
 	mov al, [ebx]
 	mov ah, WHITE_ON_BLACK
@@ -176,19 +235,20 @@ printpm:
 	popa
 	ret
 
-
 [BITS 16]
 
 
 BOOT_DRIVE		db 0
-MSG_1			db 'Bootloader is successfully running.', 0
-MSG_2			db 'Press a key to load and enter the kernel.', 0
-MSG_3			db 'Attempting to read the disk...', 0
+MSG_KB          db ' kb RAM', 0
+MSG_2			db 'Press a key to load the kernel', 0
+MSG_READ		db 'Read ', 0
+MSG_READING		db 'Reading ', 0
+MSG_FROMDISK	db ' sectors from disk', 0
 MSG_4			db 'Done!', 0
-MSG_5			db 'Entering the kernel...', 0
-DISK_ERROR		db 'The disk read failed!', 0
-INCOMPLETE_READ		db 'The wrong number of sectors were read!', 0
-HALTING			db 'Halting execution...', 0
+MSG_5			db 'PM: Entering kernel', 0
+DISK_ERROR		db 'Read failed!', 0
+HALTING			db 'Halting', 0
+NUM_BUFFER		db '000', 0
 
 times 510-($-$$) db 0
 dw 0xaa55

compile.sh

@@ -37,13 +37,13 @@ fi
 cat boot_sect.bin padded_kernel.bin > os-image
 
 echo 'checking sector count'
-actual=$(ls -l | grep "os-image" | cut -d' ' -f 7)
+actual=$(ls -l | grep "os-image" | awk '{print $5}')
 
 if [ "$use_new_bootloader" = true ]; then
-    loaded=$(grep "NUM_SECTORS equ" < bootloader_stage2.asm | cut -d' ' -f 3)
+    loaded=$(grep "NUM_SECTORS equ" < bootloader_stage2.asm |awk '{print $3}')
     actual=$((actual/512-2))
 else
-    loaded=$(grep "NUM_SECTORS equ" < boot_sect2.asm | cut -d' ' -f 3)
+    loaded=$(grep "NUM_SECTORS equ" < boot_sect2.asm | awk '{print $3}')
     actual=$((actual/512-1))
 fi