vbr: bail out on disk read error

boot/vbr.asm

@@ -58,14 +58,12 @@ _startup:
   mov ss, ax
   xor sp, sp
 
-  call print_inline
-  db "VBR: Using", 0
-
   mov [fdc.drv], dl ; backup drive number
-.adjust_chs:
+
+chs_bios:
   mov ah, 0x08
   int 0x13 ; required, QEMU detects 360kB as 1200kB with CHS 80 2 15
-  jc .noadjust ; skip if function does not exist
+  jc chs_print ; skip if function does not exist
   inc dh
   mov [fdc.nos], dh
   mov ax, cx
@@ -79,12 +77,11 @@ _startup:
   mul word [fdc.nos] ; number of tracks = number of cylinders * heads
   mul word [fdc.spt] ; number of sectors = number of tracks * sectors per track
   mov [fdc.ts], ax
+  jmp chs_print
 
+chs_print:
   call print_inline
-  db " BIOS", 0
+  db "CHS ", 0
-.noadjust:
-  call print_inline
-  db " CHS ", 0
 
   mov ax, [fdc.ts]
   div word [fdc.nos]
@@ -112,12 +109,13 @@ _startup:
   call loadrootdir
 
   call dump
+
 .end:
   hlt
   jmp .end
 
 ; Load root directory into memory
-; in	es	data segment
+; in   es      data segment
 loadrootdir:
   push bx
   push cx
@@ -142,16 +140,6 @@ loadrootdir:
   pop bx
   ret
 
-; Load a cluster from cluster offset
-; in    ax      cluster number
-;       es:bx   buffer
-loadcl:
-  mov ax, [fdc.sf]
-  mul byte [fdc.fn]
-  add ax, [fdc.rsc]
-  call print16
-  ret
-
 ; Load a single block into memory
 ; in    ax      sector number
 ;       es:bx	buffer
@@ -173,12 +161,24 @@ loadblk:
   mov dl, [fdc.drv] ; driver number
   mov ax, 0x0201 ; ah=0x02 al=0x01
   int 0x13
+  jc .error
   pop dx
   pop cx
   pop ax
   inc ax
   add bx, 0x0200
   ret
+.error:
+  xor al, al
+  xchg al, ah
+  call print_inline
+  db "disk error ", 0
+  call print_number
+  call print_inline
+  db 0x0A, 0x0D, 0
+.hlt:
+  hlt
+  jmp .hlt
 
 print_number:
   mov cx, 0x000A
@@ -198,6 +198,7 @@ print_number:
 
 print_inline:
   pop si
+  push ax
   push bx
 .loop:
   lodsb
@@ -210,6 +211,7 @@ print_inline:
   jmp .loop
 .end:
   pop bx
+  pop ax
   push si
   ret