diff options
Diffstat (limited to 'arch/x86/boot')
| -rw-r--r-- | arch/x86/boot/rm_seg.inc | 1 | ||||
| -rw-r--r-- | arch/x86/boot/setup.s | 101 |
2 files changed, 90 insertions, 12 deletions
diff --git a/arch/x86/boot/rm_seg.inc b/arch/x86/boot/rm_seg.inc index 40067b9..e34dc8b 100644 --- a/arch/x86/boot/rm_seg.inc +++ b/arch/x86/boot/rm_seg.inc @@ -10,4 +10,5 @@ .set SETUPLEN, 1 # Number of setup sectors .set SETUPSEG, 0x9020 # Setup address .set KERNSEG, 0x0100 # Historical load address +.set KERNSIZE, 0x1000 # Kernel size, interpret as a segment .set KERNADDR, KERNSEG * 0x10 diff --git a/arch/x86/boot/setup.s b/arch/x86/boot/setup.s index 41ba98c..74b2cc2 100644 --- a/arch/x86/boot/setup.s +++ b/arch/x86/boot/setup.s @@ -11,6 +11,8 @@ .include "bios.inc" .include "rm_seg.inc" +.set ENDSEG, KERNSEG + KERNSIZE # Where to stop loading kernel + # Define some constants for the GDT segment descriptor offsets .set CODESEG, gdt_code - gdt_start .set DATASEG, gdt_data - gdt_start @@ -58,23 +60,90 @@ _start: load_kernel: # Load our kernel BIOS_PRINT $boot_load_kern_msg - mov $0x02, %ah # Set BIOS read sector routine - mov (0), %dl # Read drive boot - mov $0x00, %ch # Select cylinder 0 - mov $0x00, %dh # Select head 0 [has a base of 0] - mov $0x02+SETUPLEN, %cl # Select sector 2 (next after the - # boot sector) [has a base of 1] - mov $0x10, %al # Read 16 sectors - mov $0x00, %bx # Load sectors to ES:BX ($KERNSEG:0) - int $0x13 # Start reading from drive - jc disk_error # If carry flag set, bios failed to read + # Load the system at $KERNSEG address: + mov $KERNSEG, %ax + mov %ax, %es # ES - starting address segment + xor %bx, %bx # BX is offset within segment + + # A few words about the algorithm: + # We read 0x10000 bytes (64 kB) and overflow BX (16 bytes register), + # then add 0x1000 to ES reg, after that compare with $ENDSEG + # + # If KERNSIZE != 0x10000 * N we read some unnecessary data, but + # i think it's not a problem +repeat_read: + mov %es, %ax + cmp $ENDSEG, %ax + jae enable_a20 # Jump if AX >= $ENDSEG +get_sects_for_read: + mov sectors, %ax # AX = amount of sectors - current sector + sub csect, %ax # AX has 6 significant bytes + mov %ax, %cx # Calculate how many bytes we get by + # reading AX sectors + shl $9, %cx # One sector = 2^9 = 512 + add %bx, %cx # CX = 0@@@.@@@0.0000.0000 + BX + jnc read_sects # if not overflow, then jump + jz read_sects # if CX = 0, then jump + xor %ax, %ax # AX = 0 + sub %bx, %ax # AX = amount of sectors that we must + shr $9, %ax # read for overflow BX +read_sects: + call read_track # INPUT: AX + mov %ax, %cx # CX = amount of sectors that we read + add csect, %ax + cmp sectors, %ax # Current sector = amount of sectors? + jne check_read # If not equal, jump + mov chead, %ax + cmp heads, %ax # Current head = amount of heads? + jne inc_chead # If not equal, jump + movw $0xffff, chead # Current head will overflow and equal 0 + # after INC instuction in inc_chead + incw ctrack # Go to next cylinder + # We don't check cylinder overflow + # because it makes no sense +inc_chead: + incw chead + xor %ax, %ax +check_read: + mov %ax, csect # Calculate how many bytes we get by + shl $9, %cx # reading AX sectors + add %cx, %bx # Add it to BX + jnc repeat_read # If BX not overflow, jjmp + mov %es, %ax + add $0x1000, %ax # We read 0x10000 = 65536 bytes + mov %ax, %es + xor %bx, %bx + jmp repeat_read - cli # Switch of interrupt until we have set - # up the protected mode interrupt vector +# INPUT: +# AX - amount of sectors that we want to read +read_track: + push %ax + push %bx + push %cx + push %dx + mov ctrack, %dx + mov csect, %cx # Set sector + inc %cx # Add +1 because sector has a base of 1 + mov %dl, %ch # Set cylinder + mov chead, %dh # Set head + mov %dl, %dh + mov (0), %dl # Set boot + mov $0x02, %ah # Set BIOS read sector routine + int $0x13 + jc . # Error :( + pop %dx + pop %cx + pop %bx + pop %ax + ret enable_a20: BIOS_PRINT $enable_a20_msg + cli # Switch of interrupt until we have set + # up the protected mode interrupt vector + call wait_input mov $READ_OUTP, %al out %al, $0x64 @@ -159,6 +228,14 @@ heads: # 8 significant bytes sectors: # 6 significant bytes .word 0x0 +# The number of the current component with which we interact: +ctrack: # track/cylinder + .word 0x0 +chead: + .word 0x0 +csect: + .word 1 + SETUPLEN + gdt_descriptor: # The 6-byte GDT structure containing: # - GDT size, 2 bytes (size always less one of the real size): |