Read disk geometry and DPT from BIOS

kernel/drive.asm

@@ -9,12 +9,14 @@ dskseek:	resd 1
 dskbuf:		resb 512
 
 dpt:		resb DPTSIZE
+bpb:		resb BPBSIZ4
 
 section .text
 
 ret:		ret
 
 		; Convert drive number into DL for int 13h
+		; A=0, B=1, C=0x80
 		; IN	dl	dos drive number
 		; OUT	dl	bios drive number
 getdl:		cmp dl, 2
@@ -22,6 +24,22 @@ getdl:		cmp dl, 2
 		mov dl, 0x80
 		ret
 
+		; Ask BIOS for drive parameters
+		; IN	dl	dos drive number
+		; OUT	CX,DH	chs data
+		;	ES:DI	DPT if floppy
+qrychs:		mov ah, 8
+		les di, [0x1E*4]
+		int 0x13
+		jc .defs
+		test cl, cl
+		jz .defs
+		ret
+
+.defs:		mov cx, 0x2709 ; max track = 39, max sec = 9
+		mov dh, 1 ; 2 heads
+		ret
+
 		; select drive
 		; IN	dl	drive number
 dsksel:		cmp dl, byte [dsknum]
@@ -30,15 +48,31 @@ dsksel:		cmp dl, byte [dsknum]
 		call dskrst
 
 		call getdl
-		mov ah, 8
-		les di, [0x1E*4]
-		int 0x13
+		push dx
+		call qrychs
 
-		; copy dpt
-		mov bx, di
+		; store CHS data in BPB
+		xor ax, ax
+		mov al, cl
+		mov [bpb+BPBSPT], ax
+		mov al, dh
+		inc ax
+		mov [bpb+BPBNOS], ax
+
+		; get dpt from bios if not hdd
+		pop dx
+		test dl, 0x80
+		jnz .nodpt
+		push dx
 		mov dx, dpt
+		mov bx, di
 		mov cx, DPTSIZE
 		call lod
+		mov ax, [bpb+BPBSPT]
+		mov [dpt+DPTSPT], al
+		pop dx
+.nodpt:
+
 
 		ret
 

kernel/far.asm

@@ -1,12 +1,19 @@
+; Utilities to help with far pointers
+
+; exchange DS:SI with ES:DI
+xchgs:	push ds
+	push es
+	pop ds
+	pop es
+	xchg si, di
+	ret
+
 ; far pointer load
 ; IN	ES:BX	far pointer to data
 ;	CX	number of bytes to copy
 ;	0:DX	destination buffer
-; only CX is trashed
 
-lod:	push si
-	push di
-	push es
+lod:	push es
 
 	; ES:DI := DS:DX
 	mov ax, ds
@@ -25,8 +32,6 @@ lod:	push si
 	mov ds, cx
 
 	pop es
-	pop di
-	pop si
 	ret
 
 ; far pointer store
@@ -35,18 +40,8 @@ lod:	push si
 ;	0:DX	source buffer
 ; only CX is trashed
 
-sto:	push si
-	push di
-
-	mov si, dx
+sto:	mov si, dx
 	mov di, bx
-
-	; do the copy
-	pushf
 	cld
 	rep movsb
-	popf
-
-	pop di
-	pop si
 	ret