Add small ATA driver to load kernel

Write ata_lba_read routine to load 100 disk sectors from the disk into
memory address 0x00100000 (1MiB).

Once the data is loaded, jump to that Address

Signed-off-by: Carlos Maiolino <[email protected]>

1 files changed, 67 insertions, 3 deletions

diff --git a/src/boot/bootloader.asm b/src/boot/bootloader.asm
index eb226a6..4b803fa 100644
--- a/src/boot/bootloader.asm
+++ b/src/boot/bootloader.asm
@@ -36,15 +36,13 @@ step2:
 	or eax, 0x1
 	mov cr0, eax
 
-	jmp $
-;	jmp CODE_SEG:start_32
+	jmp CODE_SEG:start_32
 
 ; GDT table description
 gdt_start:
 gdt_null:	; First segment Descriptor is always 0
 	dd 0x0
 	dd 0x0
-
 ;Second segment descriptor... Code segment - 0x8
 gdt_code:
 	dw 0xffff	; Segment limit 0-15
@@ -74,6 +72,72 @@ gdt_table:
 	dw gdt_end - gdt_start - 1
 	dd gdt_start
 
+[BITS 32]
+start_32:
+	mov eax, 1		; LBA addr to start from
+	mov ecx, 100		; Num of sectors
+	mov edi, 0x00100000	; Mem addr to load data read
+	call ata_lba_read
+	jmp CODE_SEG:0x0100000
+
+ata_lba_read:
+	; Write the high 8bits of the LBA to the disk controller
+	mov ebx, eax,
+	shr eax, 24	; Get LBA high 8bits to send to the controller
+	or eax, 0xE0	; Select the 'master' drive
+	mov dx, 0x1F6	; Port number
+	out dx, al	; Write bits to the port
+
+	; Write the number of sectors to read to the disk controller
+	mov eax, ecx	; Num of sectors
+	mov dx, 0x1F2	; Port number
+	out dx, al	; Send to the port
+
+	; Send LBA's first 0-7 bits
+	mov eax, ebx	; Get original LBA
+	mov dx, 0x1F3	; Port number
+	out dx, al	; Write the low 8 bits to the controller
+
+	; Send LBA's bits 8-15 to the controller
+	mov eax, ebx	; Get original LBA
+	mov dx, 0x1F4	; Port number
+	shr eax, 8	; Get bits 8-15
+	out dx, al	; Write 8 bits to controller
+
+	; Send LBA's bits 16-23 to the controller
+	mov eax, ebx	; Get original LBA
+	mov dx, 0x1F5	; Port number
+	shr eax, 16	; Get bits 16-23
+	out dx, al	; Write to the controller
+
+	; No idea what it does yet
+	mov dx, 0x1F7
+	mov al, 0x20
+	out dx, al
+
+	; Read sectors into memory
+.next_sector:
+	push ecx ; Save num of sectors
+
+	; Loop here until the controller is ready
+.try_again:
+	mov dx, 0x1f7
+	in al, dx
+	test al, 8
+	jz .try_again
+
+	mov ecx, 256
+	mov dx, 0x1F0
+	rep insw	; Read 256 words from the I/O port in DX into memory ES:EDI
+			; EDI has been set to 0x100000 above
+			; ecx controls how many words to read (w means word in ins)
+			; 256 * 2 bytes-per-word - We read a whole sector
+
+	pop ecx			; restor num of sectors
+	loop .next_sector	; This decrements ecx too
+
+	ret
+
 ; Fill in to the end and add bootloader signature
 	times 510 - ($ - $$) db 0
 	dw 0xAA55