banan-os/bootloader/bios/framebuffer.S

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.code16
.section .stage2
# kernel framebuffer information format
# .align 8
# .long 0xBABAB007
# .long -(0xBABAB007 + width + height + bpp)
# .long width (2 bytes used, 4 bytes for ease of calculation)
# .long height (2 bytes used, 4 bytes for ease of calculation)
# .long bpp (1 bytes used, 4 bytes for ease of calculation)
# scan memory 0x100000 -> 0x200000 for framebuffer information
# return:
# ax: target width
# bx: target height
# cx: target bpp
vesa_scan_kernel_image:
pushl %edx
pushl %esi
movl $0x100000, %esi
.vesa_scan_kernel_image_loop:
# check magic
cmpl $0xBABAB007, (%esi)
jne .vesa_scan_kernel_image_next_addr
# check checksum
movl 0x00(%esi), %edx
addl 0x04(%esi), %edx
addl 0x08(%esi), %edx
addl 0x0C(%esi), %edx
addl 0x10(%esi), %edx
testl %edx, %edx
jnz .vesa_scan_kernel_image_next_addr
# set return registers
movw 0x08(%esi), %ax
movw 0x0C(%esi), %bx
movw 0x10(%esi), %cx
jmp .vesa_scan_kernel_image_done
.vesa_scan_kernel_image_next_addr:
addl $8, %esi
cmpl $0x200000, %esi
jb .vesa_scan_kernel_image_loop
# zero out return registers
xorw %ax, %ax
xorw %bx, %bx
xorw %cx, %cx
.vesa_scan_kernel_image_done:
popl %esi
popl %edx
ret
# Find suitable video mode and save it in (vesa_target_mode)
vesa_find_video_mode:
pushw %ax
pushw %bx
pushw %cx
pushw %di
pushl %esi
pushl %ebp
movl %esp, %ebp
subl $6, %esp
# clear target mode and frame buffer
movw $0, (vesa_target_mode)
movl $0, (framebuffer + 0)
movl $0, (framebuffer + 4)
movl $0, (framebuffer + 8)
movl $0, (framebuffer + 12)
movw $0, (framebuffer + 16)
call vesa_scan_kernel_image
testw %ax, %ax
jz .vesa_find_video_mode_loop_modes_done
# save arguments in stack
movw %ax, -2(%ebp)
movw %bx, -4(%ebp)
movw %cx, -6(%ebp)
# get vesa information
movw $0x4F00, %ax
movw $vesa_info_buffer, %di
int $0x10
cmpb $0x4F, %al; jne .vesa_unsupported
cmpb $0x00, %ah; jne .vesa_error
# confirm that response starts with 'VESA'
cmpl $0x41534556, (vesa_info_buffer)
jne .vesa_error
# confirm that version is atleast 2.0
cmpw $0x0200, (vesa_info_buffer + 0x04)
jb .vesa_unsupported_version
movl $(vesa_info_buffer + 0x0E), %esi
movl (%esi), %esi
.vesa_find_video_mode_loop_modes:
cmpw $0xFFFF, (%esi)
je .vesa_find_video_mode_loop_modes_done
# get info of next mode
movw $0x4F01, %ax
movw (%esi), %cx
movw $vesa_mode_info_buffer, %di
int $0x10
cmpb $0x4F, %al; jne .vesa_unsupported
cmpb $0x00, %ah; jne .vesa_error
# check whether in graphics mode
testb $0x10, (vesa_mode_info_buffer + 0)
jz .vesa_find_video_mode_next_mode
# compare mode's dimensions
movw -2(%ebp), %ax; cmpw %ax, (vesa_mode_info_buffer + 0x12)
jne .vesa_find_video_mode_next_mode
movw -4(%ebp), %ax; cmpw %ax, (vesa_mode_info_buffer + 0x14)
jne .vesa_find_video_mode_next_mode
movb -6(%ebp), %al; cmpb %al, (vesa_mode_info_buffer + 0x19)
jne .vesa_find_video_mode_next_mode
# set address, pitch, type
movl (vesa_mode_info_buffer + 0x28), %esi
movl %esi, (framebuffer + 0)
movw (vesa_mode_info_buffer + 0x10), %ax
movw %ax, (framebuffer + 4)
movb $1, (framebuffer + 17)
# set width, height, bpp
movw -2(%ebp), %ax; movw %ax, (framebuffer + 8)
movw -4(%ebp), %ax; movw %ax, (framebuffer + 12)
movw -6(%ebp), %ax; movb %al, (framebuffer + 16)
movw %cx, (vesa_target_mode)
jmp .vesa_find_video_mode_loop_modes_done
.vesa_find_video_mode_next_mode:
addl $2, %esi
jmp .vesa_find_video_mode_loop_modes
.vesa_find_video_mode_loop_modes_done:
leavel
popl %esi
popw %di
popw %cx
popw %bx
popw %ax
ret
.vesa_unsupported:
movw $vesa_unsupported_msg, %si
jmp print_and_halt
.vesa_unsupported_version:
movw $vesa_unsupported_version_msg, %si
jmp print_and_halt
.vesa_error:
movw $vesa_error_msg, %si
jmp print_and_halt
# scan for video mode in kernel memory and set the correct one.
# when video mode is not found or does not exists,
# set it to 80x25 text mode to clear the screen.
.global vesa_set_video_mode
vesa_set_video_mode:
pushw %ax
pushw %bx
call vesa_find_video_mode
movw (vesa_target_mode), %bx
testw %bx, %bx
jz .vesa_set_target_mode_generic
movw $0x4F02, %ax
orw $0x4000, %bx
int $0x10
jmp .set_video_done
.vesa_set_target_mode_generic:
movb $0x03, %al
movb $0x00, %ah
int $0x10
.set_video_done:
popw %bx
popw %ax
ret
vesa_error_msg:
.asciz "VESA error"
vesa_unsupported_msg:
.asciz "VESA unsupported"
vesa_unsupported_version_msg:
.asciz "VESA unsupported version"
vesa_success_msg:
.asciz "VESA success"
.section .bss
vesa_info_buffer:
.skip 512
vesa_mode_info_buffer:
.skip 256
vesa_target_mode:
.skip 2
.global framebuffer
.align 8
framebuffer:
.skip 4 # address
.skip 4 # pitch
.skip 4 # width
.skip 4 # height
.skip 1 # bpp
.skip 1 # type