From 66289aa8ecfa07b20bad424eb9860b196641ef52 Mon Sep 17 00:00:00 2001
From: Brett Weiland <brett_weiland@bpcspace.com>
Date: Fri, 19 Mar 2021 10:54:25 -0500
Subject: first commit

---
 src/bootloader/video.asm | 179 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 179 insertions(+)
 create mode 100644 src/bootloader/video.asm

(limited to 'src/bootloader/video.asm')

diff --git a/src/bootloader/video.asm b/src/bootloader/video.asm
new file mode 100644
index 0000000..5b292c2
--- /dev/null
+++ b/src/bootloader/video.asm
@@ -0,0 +1,179 @@
+[extern _vbe_infoblock]
+vbe_init:
+.init_video:
+;getting edid
+
+mov ax, 0
+mov es, ax
+mov di, 0x500
+
+mov ax, 0x4f15
+mov bx, 0x1
+mov cx, 0 
+mov dx, 0
+
+int 0x10
+
+cmp al, 0x4f
+jne .vbe_unsupported
+cmp ah, 0x00
+jne .edid_error
+
+
+mov ah, [0x500+58]
+shr ah, 4
+mov al, [0x500+56]
+push ax
+
+mov ah, [0x500+61]
+shr ah, 4
+mov al, [0x500+59]
+push ax
+
+mov al, BYTE [0x500+20]
+test al, 0x80
+jz .res_unsupported ; uses an analog signal
+
+shr al, 4
+and al, 7
+
+.cdp_6:
+cmp al, 0b001
+jne .cdp_8
+mov ax, 18
+jmp .colordepth_found
+
+.cdp_8:
+cmp al, 0b010
+jne .cdp_10
+mov ax, 24
+jmp .colordepth_found
+
+.cdp_10:
+cmp al, 0b011
+jne .cdp_12
+mov ax, 30
+jmp .colordepth_found
+
+.cdp_12:
+cmp al, 0b100
+jne .cdp_14
+mov ax, 36
+jmp .colordepth_found
+
+.cdp_14:
+cmp al, 0b101
+jne .cdp_16
+mov ax, 42
+jmp .colordepth_found
+
+.cdp_16:
+cmp al, 0b110
+jne .cdp_undefined
+mov ax, 48
+jmp .colordepth_found
+
+.cdp_undefined:
+mov ax, 24
+; TODO print warning, this only happens when we can't find bitdepth
+
+.colordepth_found:
+push ax
+
+
+
+
+; _______________________________________________________________________________________________________
+
+; When we get things sorted out, some time you should come back here and find a good resolution that isn't
+; native as a fallback.
+; Maybe redo this part in C?
+
+;getting available modes
+mov ax, 0
+mov es, ax
+mov ax, 0x500 
+mov di, ax
+
+;get vbe capabilities
+mov ax, 0x4f00
+int 0x10
+cmp ax, 0x4f
+jne .vbe_generic_error
+cmp DWORD [0x500], "VESA"
+jne .vbe_generic_error
+
+; now we loop through the modes
+mov ebx, [0x500+14] ; pointer to modes
+mov di, 0x600
+mov ax, 0
+mov es, ax
+.mode_loop:
+mov ax, 0x4f01 
+mov cx, [ebx]
+cmp cx, 0xffff
+je .res_unsupported
+
+int 0x10
+
+mov ax, [esp]
+cmp al, BYTE [0x600+25] ; might be wrong
+jne .mode_loop_next
+
+; width (1920)
+mov ax, [esp+4]
+cmp ax, [0x600+18]
+jne .mode_loop_next
+
+; height
+mov ax, [esp+2]
+cmp ax, [0x600+20]
+jne .mode_loop_next
+
+
+
+jmp .mode_found
+
+.mode_loop_next:
+add ebx, 2
+jmp .mode_loop
+ 
+.mode_found:
+mov ax, 0x4f02 
+mov bx, cx
+int 0x10
+;getting rid of stack
+pop ax
+pop ax
+pop ax
+ret
+; ________________________________________________________________________________________________________
+
+.vbe_unsupported:
+mov bx, .unsupported_msg
+mov cx, 0
+call bios_print
+jmp $
+
+.vbe_generic_error:
+mov bx, .lazyerror_msg
+mov cx, 0
+call bios_print
+jmp $
+
+.edid_error:
+mov bx, .ediderror_msg
+mov cx, 0
+call bios_print
+jmp $
+
+.res_unsupported:
+mov bx, .res_unsupported_msg
+mov cx, 0
+call bios_print
+jmp $
+
+.unsupported_msg: db "Your BIOS doesn't support VESA. It's probably time to get a new computer!", 0
+.lazyerror_msg: db "A VESA error has occured.", 0
+.ediderror_msg: db "EDID error", 0
+.res_unsupported_msg: db "Native resolution not supported!", 0
-- 
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