fix bug with skipping over sectors

it uses selfmodifying code so the visualization is blinking
it's a feature ok

Makefile

@@ -1,11 +1,16 @@
 boot.bin: boot.o
-	ld -o $@ --oformat binary -Ttext 0x7c00 $<
+	ld -o $@ --oformat binary -Ttext 0x7000 $<
 
 boot.o: boot.s
 	as -o $@ $<
 
+floppy.bin: boot.bin floppy_base.bin
+	rm -vf $@
+	cp floppy_base.bin $@
+	dd if=boot.bin of=$@ conv=notrunc
+
 .PHONY: boot disasm hexdump
-boot: boot.bin
+boot: floppy.bin
 	qemu-system-i386 -drive file=$^,index=0,if=floppy,format=raw
 
 disasm: boot.bin

boot.s

@@ -1,100 +1,261 @@
 .code16
+# the currently viewed sector gets put at 0x7c00
+# we move to 0x7000 to make space
 
 .global _start # the linker needs to find it
 _start:
-	jmp vga_init
+	jmp move_self
 	.ascii "the bootsector" # CAN AFFECT MANUALLY SET POINTER, LEAVE AT THIS LEN
 
 _Xterm_grad:
 	.byte 0x00, 0x5f / 4, 0x87 / 4, 0xaf / 4, 0xd7 / 4, 0xff / 4
 
+# saves some work later on when i'll want to execute sectors
+move_self:
+	mov $512, %si
+move_self_loop:
+	movb 0x7c00(%si), %ah
+	movb %ah, 0x7000(%si)
+	dec %si
+	jnz move_self_loop
+	jmp (vga_init-0xc00) # correct IP
+
 vga_init:
 	# enter mode 13h
 	mov $0x13, %ax
 	int $0x10
 
-	# prepare the xterm palette 16-231
-	# bh - color id
-	# dx - used up for the port number
-	mov $16, %bh
-	xor %ch, %ch
 
-	mov $0x7c1, %ax # pointer to _Xterm_grad
-	mov %ax, %ds
-palette_loop:
+	# prepare the xterm palette 0-15
+	# 7 and 8 aren't right, TODO
+	# bl - counter rgb
+	xor %bh, %bh
+
+palette1_loop:
 	mov %bh, %al
+	mov %al, %ah
 	mov $0x3c8, %dx
 	out %al, %dx
 	inc %dx
+	mov $3, %bl
+palette1_color:
+	xor %al, %al # 0 al
+	shr $1, %ah  # sets carry to the lost bit
+	adc $0, %al  # add carry to %al, setting it to the carry flag
+_palette1_sal:
+	sal $5, %al
+	sub $1, %al # this gets changed to 6 in the second half
+	            # it will increase the lightness
+	adc $0, %al
+	out %al, %dx
+	dec %bl
+	jnz palette1_color
+	cmp $8, %bh
+	jne palette1_not7
+	inc _palette1_sal+2
+palette1_not7:
+	inc %bh
+	jnz palette1_loop
 
+
+	# prepare the xterm palette 16-231
+	# ch - color id
+	# dx - used up for the port number
+	mov $16, %ch
+
+	mov $0x701, %ax # pointer to _Xterm_grad
+	mov %ax, %ds
+palette_loop:
+	mov %ch, %al
+	dec %dx # we can reuse the %dx from the previous loop
+	out %al, %dx
+	inc %dx
 	sub $16, %al # the colors start at 16, real_id = id - 16
 	mov $6, %bl
-
 	xor %ah, %ah
 	div %bl      # al = real_id / 6
 	             # ah = remainder
 	mov %ah, %cl # cl = real_id % 6
-
 	xor %ah, %ah
 	div %bl      # al = real_id / 6 / 6
 	             # ah = remainder
-	
 	# at this point
 	#   al - R
 	#   ah - G
 	#   cl - B
-
-	mov %cl, %bl # stash %cl in %bl
-
-	mov %al, %cl # output R
-	mov %cx, %si
-	mov (%si), %al
+	# here i'm assuming that %bh is 0, because the loop above clears it
+	mov %al, %bl # output R
+	mov (%bx), %al
 	out %al, %dx
-
-	mov %ah, %cl # G
-	mov %cx, %si
-	mov (%si), %al
+	mov %ah, %bl # G
+	mov (%bx), %al
 	out %al, %dx
-
-	mov %bl, %cl # B
-	mov %cx, %si
-	mov (%si), %al
+	mov %cl, %bl # B
+	mov (%bx), %al
 	out %al, %dx
-
-	inc %bh
+	inc %ch
 	jnz palette_loop # loop until 0
-	# TODO first 16 + grayscale
 
-before_loop:
-	mov $0xA000, %ax # ES = vga memory
-	mov %ax, %es
 
-	mov $0x7c0, %ax # DS = the bootsector
+	# %ah stores the current shade
+	# %ch iterator
+	mov $2, %ah
+	mov $232, %ch
+# the pattern i'm aiming for is
+# [2, 5, 7, 10, 12, 15, 17, 20, 22, 25, 27, 30, 32, 35, 37, 40, 42, 45, 47, 50, 52, 55, 57, 60]
+#    +3 +2  +3  +2  +3  +2  +3  +2  +3  +2  +3  +2  +3  +2  +3  +2  +3  +2 ...
+palette_greys:
+
+	mov %ch, %al
+	dec %dx
+	out %al, %dx
+	inc %dx
+	mov %ah, %al
+	out %al, %dx
+	out %al, %dx
+	out %al, %dx
+	add $2, %ah # TODO this is obviously wrong
+	inc %ch
+	jnz palette_greys
+	
+
+	mov $0xA000, %ax # DS = vga memory
 	mov %ax, %ds
 
+	mov $0x7c0, %ax # ES = the bootsector
+	mov %ax, %es
+
+update_screen_vgay:
+	mov $0, %dh
+
+# "arguments":
+#  %es - has the sector at 0-512
+#  %dh - vga Y, should be either 0 or more than 25
+
+update_screen:
+.set SCALE, 6
+.set TEXT_X, 0
+.set TEXT_CLR, 102
+.set IMG_X, 128
+.set IMG_Y, 0
+	# %bl/h - scale iterators
+	# %al - current byte
 	# %si - position in sector
 	# %di - position in vga mem
+	# %dl - text X
 	mov $0, %si
-	mov $0, %di
-loop:
-	movb %ds:(%si), %cl
-	movb %cl, %es:(%di)
+	mov $320*IMG_Y+IMG_X, %di
+	mov $TEXT_X, %dl
 
+render_loop:
+	movb %es:(%si), %al
+	mov $SCALE, %bh
+y_loop:
+	mov $SCALE, %bl
+x_loop:
+	movb %al, %ds:(%di)
 	inc %di
-	mov $16, %cl # if we've crossed a 16 pixel boundary, skip to the next line
-	and %di, %cx
-	jz not_eol
-	add $304, %di
+	dec %bl # loop ctr
+	jnz x_loop
+
+	add $320-SCALE, %di
+	dec %bh
+	jnz y_loop
+	sub $(320-1)*SCALE, %di
+
+	# text preview
+	cmp $25, %dh # the screen only has 25 lines, we can't render more
+	jnb text_overflow
+	mov $TEXT_CLR, %bl # update %bl with the text color
+	mov $0x2, %ah      # move cursor (the position is already loaded)
+	int $0x10
+	mov $0xe, %ah      # and print the charactr (again, already in the correct register)
+	int $0x10
+text_overflow:
+
+	inc %dl # text forward
+	inc %si # sector forward
+
+	mov $15, %cl  # check if %si is a multiple of 16
+	and %si, %cx
+	jnz not_eol              # if it is, then we've finished the current row
+	add $(320-16)*SCALE, %di # go down in visualization
+	mov $TEXT_X, %dl         # text back to left
+	inc %dh                  # and text down
 not_eol:
-	inc %si      # only iterate 512 times
+
 	cmp $512, %si
-	jl loop
+	jl render_loop
 
-	incb %es:319
-end:
-	hlt
-	jmp end
 
-# .fill (510-(.-_start))/4, 4, 0xc4c5c6c7 # color stripes for testing
+	# print sector number
+	int $0x10 # wild assumption - %ah == 0xe
+	int $0x10 # printing some garbage to make this line up
+	int $0x10
+	mov %cs:_sector_num+1, %cx
+	mov $4, %dl # loop counter
+
+	mov $231, %bl # TODO can be removed if i change the loop condition higher up
+digit_loop:
+	mov %cx, %ax
+	mov $10, %dh  # base 10
+	div %dh       # %al = quotient ; %ah = remainder
+	ror $8, %ax   # swap those around
+	add $'0', %al
+	mov %ah, %cl  # save remainder
+	xor %ch, %ch
+	mov $0xe, %ah
+	int $0x10
+
+	mov $'\b', %al # backspace two times
+	int $0x10
+	int $0x10
+	dec %dl
+	jnz digit_loop
+
+
+	mov $0, %ah # read character
+	int $0x16
+	# scancode in %ah
+	cmp $0x4d, %ah # right arrow?
+	jne 1f
+
+	incw %cs:_sector_num+1
+read_sector:
+_sector_num:
+	movw $0, %ax  # sector num (0indexed)
+	movb $18, %ch # divide by 18 (sectors / track)
+	div %ch
+	# %ah - sector
+	# %al - track * 2, 1st bit - head
+
+	mov $0x100, %dx # head / drive number
+	and %al, %dh
+	sar $1, %al
+
+	mov %al, %ch # track
+	mov %ah, %cl # sector
+	inc %cl      # sectors are 1indexed
+
+	mov $1, %al  # read only one sector
+	xor %bx, %bx # write to es:bx
+
+#	mov $0, %ah # reset disk system
+#	int $0x13
+	mov $2, %ah # actual read
+	int $0x13 # TODO error checking
+	jmp update_screen_vgay
+
+1:
+	# not the right arrow
+	# left arrow?
+	cmp $0x4b, %ah
+	jne 1f
+	decw %cs:_sector_num+1 # it is, decrease sector and read
+	jmp read_sector
+1:  # default: scroll text
+	xorb $-7, %cs:update_screen_vgay+1
+	jmp update_screen_vgay
+
 .fill 510-(.-_start), 1, 0x90 # fill with 0x90 (NOPs)
 .word 0xaa55                  # boot sector magic