BIOS 13h video mode draw pixels

README.md

@@ -17,6 +17,8 @@ Hello world programs that run without an operating system.
         1.  [background](bios_background.S)
         1.  [scroll](bios_scroll.S)
             1.  [clear screen](bios_clear_screen.S)
+        1.  [pixel](bios_pixel.S)
+            1.  [pixel line](bios_pixel_line.S)
     1.  APM
         1.  [APM shutdown](apm_shutdown.S)
         1.  [APM shutdown 2](apm_shutdown2.S)

TODO.md

@@ -1,20 +1,35 @@
 # TODO
 
 -   Segment registers: http://stackoverflow.com/questions/30549526/c-kernel-works-fine-on-vm-but-not-actual-computer?rq=1
--   32 bit mode. Answer http://stackoverflow.com/questions/7130726/writing-a-hello-world-kernel
+
+    - http://stackoverflow.com/questions/4903906/assembly-using-the-data-segment-register-ds answer with minimal example and mention QEMU vs real hardwre http://wiki.osdev.org/Segmentation
+    - http://stackoverflow.com/questions/3819699/what-does-ds40207a-mean-in-assembly
+
+-   move to 32 bit mode. Answer http://stackoverflow.com/questions/7130726/writing-a-hello-world-kernel
+
+-   load a second stage from disk into memory
+
 -   BIOS
+
     - pages
+
 -   ACPI
+
     -   reboot computer. Would put QEMU into an infinite reboot loop. Awesome.
+
 -   multithreading: http://stackoverflow.com/questions/7308391/how-is-concurrency-done-in-intel-x86-assembly || http://stackoverflow.com/questions/980999/what-does-multicore-assembly-language-look-like || http://stackoverflow.com/questions/714905/threads-in-x86-assembler-using-the-gnu-assember-as || https://github.com/cirosantilli/oszur11-operating-system-examples/tree/1af6451852887fac3d7206d4d09714c181c81d1e/Chapter_07_Threads
+
 -   transition to protected mode
+
     - test the paging circuit
+
 -   play with hardware
-    -   set a pixel on screen
-        - http://wiki.osdev.org/How_do_I_set_a_graphics_mode
-        - http://stackoverflow.com/questions/14419088/assembly-draw-a-pixel-on-the-screen-in-protected-mode
+
+    -   set a pixel on screen in protected mode http://stackoverflow.com/questions/14419088/assembly-draw-a-pixel-on-the-screen-in-protected-mode
     -   USB
     -   networking
     -   GPU...
+
 -   outb inb instructions
+
 -   POST https://en.wikipedia.org/wiki/Power-on_self-test

bios.md

@@ -18,6 +18,31 @@ Does any documentation or portability exist??
 
 <http://www.scs.stanford.edu/nyu/04fa/lab/specsbbs101.pdf> says little about interrupts, I don't understand it's scope.
 
+## Video mode
+
+There are several video modes.
+
+Modes determine what interrupt functions can be used.
+
+There are 2 main types of modes:
+
+- text, where we operate character-wise
+- video, operate byte-wise
+
+Modes can be set with `int 0x10` and `AH = 0x00`, and get with `AH = 0x0F`
+
+The most common modes seem to be:
+
+- 0x01: 40x25 Text, 16 colors, 8 pages
+- 0x03: 80x25 Text, 16 colors, 8 pages
+- 0x13: 320x200 Graphics, 256 colors, 1 page
+
+You can add 128 to the modes to avoid clearing the screen.
+
+Taken from: <https://courses.engr.illinois.edu/ece390/books/labmanual/graphics-int10h.html>
+
+A larger list: <http://www.columbia.edu/~em36/wpdos/videomodes.txt>
+
 ## Colors
 
 ## Text properties

bios_clear_screen.S

@@ -4,18 +4,20 @@
 BEGIN
 
 /*
-Print one 'a' char to ensure that something will be claered.
+Print one 'a' char to ensure that something will be cleared.
 
 On some systems, BIOS messages get automatically cleared. Not the case for QEMU 2.0.0.
 */
 PUTC(61)
 
+/* Scroll 0 is magic, and scrolls the entire selected rectangle. */
 mov $0x0600, %ax
 mov $0xA4, %bh
 
 /*
-Act on the entire screen.
-Bottom right is at (24,79) == (0x18,0x4F)
+Pick the entire screen.
+Bottom right is at (24,79) == (0x18,0x4F),
+since we are on the default mode.
 */
 mov $0x0000, %cx
 mov $0X184F, %dx

bios_pixel.S

@@ -0,0 +1,52 @@
+/*
+Set pixel at position (1, 1) to a clear red color (0Ch) in 13h video mode.
+
+You have to look a bit hard to see it.
+
+Mode 13h has: 320x200 Graphics, 256 colors, 1 page.
+
+https://en.wikipedia.org/wiki/Mode_13h describes it a bit.
+
+TODO Color encoding: is there any logic?
+Shown on wiki page: https://en.wikipedia.org/wiki/Mode_13h
+Does not seem to be R  R  R  G  G  G  B  B mentioned at: https://en.wikipedia.org/wiki/8-bit_color
+Asked at: http://stackoverflow.com/questions/14233437/convert-normal-256-color-to-mode-13h-version-color
+
+Things get much more involved from protected mode:
+http://stackoverflow.com/questions/14419088/how-to-draw-a-pixel-on-the-screen-in-protected-mode-in-x86-assembly
+TODO do it!
+
+And for hardware accelaration, you need to make real drivers
+(to semi-documented complex GPU hardware :-) )
+http://wiki.osdev.org/How_do_I_set_a_graphics_mode
+*/
+
+#include "common.h"
+BEGIN
+    /* Enter video mode 13h: */
+    mov $0x0013, %ax
+    int $0x10
+start:
+    /*
+    Draw the pixel pixel.
+
+    AH = 0Ch
+    AL = Color
+    BH = Page Number
+    CX = x
+    DX = y
+    */
+    mov $0x0C0C, %ax
+    mov $0x01, %bh
+    mov $0x0001, %cx
+    mov $0x0001, %dx
+    int $0x10
+
+    inc %cx
+    inc %dx
+    cmp $201, %dx
+    jz end
+    jmp start
+end:
+    hlt
+END

bios_pixel_line.S

@@ -0,0 +1,22 @@
+/*
+Draw a 45 degree line of pixels to the screen on 13h video mode.
+*/
+
+#include "common.h"
+BEGIN
+    mov $0x0013, %ax
+    int $0x10
+    mov $0x0000, %cx
+    mov $0x0000, %dx
+start:
+    mov $0x0C88, %ax
+    mov $0x01, %bh
+    int $0x10
+    inc %cx
+    inc %dx
+    cmp $201, %dx
+    jz end
+    jmp start
+end:
+    hlt
+END