+mainsz_msg: .asciz "Main program size: "
+mainsz_msg2: .asciz " ("
+mainsz_msg3: .asciz " sectors)\n"
+
+first_sect: .long 0
+sect_left: .long 0
+cur_track: .long 0
+trk_sect: .long 0
+dest_ptr: .long 0
+
+load_main:
+ movl $main_load_addr, dest_ptr
+
+ # calculate first sector
+ mov $_boot2_size, %eax
+ add $511, %eax
+ shr $9, %eax
+ # add 1 to account for the boot sector
+ inc %eax
+ mov %eax, first_sect
+
+ # calculate the first track (first_sect / sect_per_track)
+ movzxw sect_per_track, %ecx
+ xor %edx, %edx
+ div %ecx
+ mov %eax, cur_track
+ # remainder is sector within track
+ mov %edx, trk_sect
+
+ mov $mainsz_msg, %esi
+ call putstr
+ mov $_main_size, %eax
+ mov %eax, %ecx
+ call print_num
+
+ mov $mainsz_msg2, %esi
+ call putstr
+
+ # calculate sector count
+ add $511, %eax
+ shr $9, %eax
+ mov %eax, sect_left
+
+ call print_num
+ mov $mainsz_msg3, %esi
+ call putstr
+
+ # read a whole track into the buffer (or partial first track)
+ldloop:
+ movzxw sect_per_track, %ecx
+ sub trk_sect, %ecx
+ push %ecx
+ call read_track
+
+ # debug: print the first 32bits of the track
+ #mov buffer, %eax
+ #call print_num
+ #mov $10, %al
+ #call putchar
+
+ # copy to high memory
+ mov $buffer, %esi
+ mov dest_ptr, %edi
+ mov (%esp), %ecx
+ shl $9, %ecx
+ add %ecx, dest_ptr
+ shr $2, %ecx
+ addr32 rep movsl
+
+ incl cur_track
+ # other than the first track which might be partial, all the rest start from 0
+ movl $0, trk_sect
+
+ pop %ecx
+ sub %ecx, sect_left
+ ja ldloop
+
+ # the BIOS might have enabled interrupts
+ cli
+
+ # just in case we were loaded from floppy, turn all floppy motors off
+ mov $0x3f2, %dx
+ in %dx, %al
+ and $0xf0, %al
+ out %al, %dx
+
+ mov $10, %ax
+ call putchar
+
+ ret
+
+rdtrk_msg: .asciz "Reading track: "
+rdcyl_msg: .asciz " - cyl: "
+rdhead_msg: .asciz " head: "
+rdsect_msg: .asciz " start sect: "
+rdlast_msg: .asciz " ... "
+rdok_msg: .asciz "OK\n"
+rdfail_msg: .asciz "failed\n"
+
+read_retries: .short 0
+
+ .set drive_number, 0x7bec
+read_track:
+ # set es to the start of the destination buffer to allow reading in
+ # full 64k chunks if necessary
+ mov $buffer, %bx
+ shr $4, %bx
+ mov %bx, %es
+ xor %ebx, %ebx
+
+ movw $3, read_retries
+
+read_try:
+ # print track
+ mov $rdtrk_msg, %esi
+ call putstr
+ mov cur_track, %eax
+ call print_num
+ mov $rdcyl_msg, %esi
+ call putstr
+
+ # calc cylinder (cur_track / num_heads) and head (cur_track % num_heads)
+ mov cur_track, %eax
+ movzxw num_heads, %ecx
+ xor %edx, %edx
+ div %ecx
+
+ # print cylinder
+ push %eax
+ call print_num
+ # print head
+ mov $rdhead_msg, %esi
+ call putstr
+ movzx %dx, %eax
+ call print_num
+ pop %eax
+
+ # head in dh
+ mov %dl, %dh
+
+ # cylinder low byte at ch and high bits at cl[7, 6]
+ mov %al, %ch
+ mov %ah, %cl
+ and $3, %cl
+ ror $2, %cl
+
+ # print start sector
+ mov $rdsect_msg, %esi
+ call putstr
+ mov trk_sect, %eax
+ call print_num
+ mov $rdlast_msg, %esi
+ call putstr
+
+ # start sector (1-based) in cl[0, 5]
+ mov trk_sect, %al
+ inc %al
+ and $0x3f, %al
+ or %al, %cl
+
+ # number of sectors in al
+ mov 2(%esp), %ax
+ # call number (2) in ah
+ mov $2, %ah
+ # drive number in dl
+ movb drive_number, %dl
+ int $0x13
+ jnc read_ok
+
+ # abort after 3 attempts
+ decw read_retries
+ jz read_fail
+
+ # error, reset controller and retry
+ xor %ah, %ah
+ int $0x13
+ jmp read_try
+
+read_fail:
+ mov $rdfail_msg, %esi
+ call putstr
+ jmp abort_read
+
+read_ok:
+ mov $rdok_msg, %esi
+ call putstr
+
+ # reset es to 0 before returning
+ xor %ax, %ax
+ mov %ax, %es
+ ret
+
+str_read_error: .asciz "Read error while reading track: "
+
+abort_read:
+ mov $str_read_error, %esi
+ call putstr
+ mov cur_track, %eax
+ call print_num
+ mov $10, %al
+ call putchar
+
+ cli
+0: hlt
+ jmp 0b
+
+
+ # better print routines, since we're not constrainted by the 512b of
+ # the boot sector.
+ .global cursor_x
+ .global cursor_y
+cursor_x: .long 0
+cursor_y: .long 0
+
+putchar:
+ pushal
+ call ser_putchar
+
+ cmp $10, %al
+ jnz 0f
+ call video_newline
+ jmp 1f
+
+0: push %eax
+ mov cursor_y, %eax
+ mov $80, %ecx
+ mul %ecx
+ add cursor_x, %eax
+ mov %eax, %ebx
+ pop %eax
+
+ mov $0xb8000, %edx
+
+ # this looks retarded. in nasm: [ebx * 2 + edx]
+ mov %al, (%edx, %ebx, 2)
+ movb $7, 1(%edx, %ebx, 2)
+ incl cursor_x
+ cmpl $80, cursor_x
+ jnz 1f
+ call video_newline
+
+1: popal
+ ret
+
+ # expects string pointer in esi
+putstr:
+ mov (%esi), %al
+ cmp $0, %al
+ jz 0f
+ call putchar
+ inc %esi
+ jmp putstr
+0: ret