working on the boot loader

diff --git a/src/boot/boot.s b/src/boot/boot.s
index ffd1408..499c386 100644 (file)
--- a/src/boot/boot.s
+++ b/src/boot/boot.s
@@ -12,6 +12,8 @@
        mov %ax, %ds
        mov %ax, %es
 
+       mov %dl, drive_number
+
        call clearscr
 
        mov $_boot2_size, %eax
@@ -32,7 +34,7 @@
        shr $4, %bx
        mov %bx, %es
        xor %bx, %bx
-       call readsect
+       call read_sect
        jmp boot2_addr
 
        cli
@@ -42,39 +44,67 @@
 
        .set ARG_NSECT, 6
        .set ARG_SIDX, 4
-       .set VAR_NTRACKS, -2
 
-# readsect(first, num)
-readsect:
+# read_sect(first, num)
+read_sect:
+       push %bp
+       mov %sp, %bp
+
+       mov ARG_SIDX(%bp), %ax
+       mov ARG_NSECT(%bp), %cx
+
+       jmp 1f
+0:     push %ax
+       call read_sector
+       add $2, %sp
+1:     cmp ARG_NSECT(%bp), %cx
+       jnz 0b
+
+       pop %bp
+       ret
+
+# read_sector(sidx)
+read_sector:
        push %bp
        mov %sp, %bp
-       sub $2, %sp
+       push %cx
+       push %dx
 
-       # calculate how many tracks to read
-       mov ARG_NSECT(%bp), %ax
+       # calculate the track (sidx / sectors_per_track)
+       mov 4(%bp), %ax
        xor %dx, %dx
        mov $SECT_PER_TRACK, %cx
        div %cx
-       cmp $0, %dx
-       jz 0f
-       inc %ax
-0:     mov %ax, VAR_NTRACKS(%bp)
+       mov %ax, %cx
+       # save the remainder in ax
+       mov %dx, %ax
+       # head in dh
+       mov %cl, %dh
+       and $1, %dh
+       # cylinder (track/2) in ch [0-7] and cl[6,7]<-[8,9]
+       rol $7, %cx
+       ror $2, %cl
+       and $0xc0, %cl
+       # sector num cl[0-5] is sidx % sectors_per_track (saved in ax)
+       inc %al
+       or %al, %cl 
+       # ah = 2 (read), al = 1 sectors
+       mov $0x0201, %ax
+       movb drive_number, %dl
+       int $0x13
+
+       # increment es:bx accordingly (advance es if bx overflows)
+       add $512, %bx
+       jno 0f
+       mov %es, %ax
+       add $4096, %ax
+       mov %ax, %es
 
-       xor %cx, %cx
-0:     cmp VAR_NTRACKS(%bp), %cx
-       jz 0f
-       push %cx
-       call read_track
+       pop %dx
        pop %cx
-       jmp 0b
-0:
-       # TODO cont.
        pop %bp
        ret
 
-read_track:
-       ret
-
 clearscr:
        push %es
        pushw $0xb800
@@ -86,6 +116,7 @@ clearscr:
        pop %es
        ret
 
+# expects number in eax
 print_num:
        # save es
        push %es
@@ -122,6 +153,7 @@ print_num:
        pop %es
        ret
 
+drive_number: .byte 0
 numbuf: .space 10
        .org 510
        .byte 0x55