Reorder disk access and fix missing si setting

boot/kernel.asm

@@ -143,32 +143,16 @@ drvoff:	dd 0 ; partition offset
 drvpos:	dd 0 ; absolute physical sector number
 buffer:	times 512 db 0
 
-	; Select active drive
+	; Convert between drive number and BIOS dl
-	; IN	dl	drive number A=0, B=1, C=2, ...
+	; Bidirectional mapping
-select:	mov [drvnum], dl
+	; 0 <-> 0, 1 <-> 1, 2 <-> 0x80, 3 <-> 0x81
-	push es
+dnconv:	mov cx, 7
-	xor ax, ax
+	ror dx, 1
-	push cs
+	rol dl, 1
-	pop es
+dncl:	rcl dl, 1
-	stosw
+	rcr dh, 1
-	stosw
+	loop dncl
-	stosw
+	xchg dh, dl
-	stosw
-	pop es
-	call read
-	call ldbpb
-	ret
-
-	; load bpb from buffer to bpb
-ldbpb:	push ds
-	push es
-	mov ax, cs
-	mov si, buffer+0x0B
-	mov di, bpb
-	mov cx, bpb_len
-	rep movsb
-	pop es
-	pop ds
 	ret
 
 	; Set sector number
@@ -183,9 +167,9 @@ read:	; this uses the EBIOS extensions
 	xor ax, ax
 	push ax
 	push ax
-	mov ax, [drvpos+2]
+	mov ax, [cs:drvpos+2]
 	push ax
-	mov ax, [drvpos]
+	mov ax, [cs:drvpos]
 	push ax
 
 	; dword target buffer
@@ -203,25 +187,41 @@ read:	; this uses the EBIOS extensions
 
 	mov si, sp
 	mov ah, 0x42
-	mov dl, [drvnum]
+	mov dl, [cs:drvnum]
 	call dnconv
 	stc
 	int 0x13
 
 	add sp, di
-
 	ret
 
-	; Convert between drive number and BIOS dl
+	; Select active drive
-	; Bidirectional mapping
+	; IN	dl	drive number A=0, B=1, C=2, ...
-	; 0 <-> 0, 1 <-> 1, 2 <-> 0x80, 3 <-> 0x81
+select:	mov [cs:drvnum], dl
-dnconv:	mov cx, 7
+	ret
-	ror dx, 1
+	push es
-	rol dl, 1
+	xor ax, ax
-dncl:	rcl dl, 1
+	push cs
-	rcr dh, 1
+	pop es
-	loop dncl
+	mov si, drvoff
-	xchg dh, dl
+	stosw
+	stosw
+	stosw
+	stosw
+	pop es
+	call read
+	; load bpb from buffer to bpb
+ldbpb:	push ds
+	push es
+	mov ax, cs
+	mov ds, ax
+	mov es, ax
+	mov si, buffer+0x0B
+	mov di, bpb
+	mov cx, bpb_len
+	rep movsb
+	pop es
+	pop ds
 	ret
 
 init:	cli
@@ -232,7 +232,6 @@ init:	cli
 	xor sp, sp
 
 	call dnconv
-	int 3
 	call select
 	int 3
 	mov ax, [cs:bpb+bpb_ss]