Add support for 320x200 256 color VGA video mode

Author: phil-opp

Cargo.lock

@@ -15,6 +15,15 @@ x86_64 = "0.2.7"
 usize_conversions = "0.2.0"
 fixedvec = "0.2.3"
 
+[dependencies.font8x8]
+version = "0.2.4"
+default-features = false
+features = ["unicode"]
+
+[features]
+default = []
+vga_320x200 = []
+
 [profile.dev]
 panic = "abort"
 

Cargo.toml

@@ -14,6 +14,7 @@ extern crate x86_64;
 extern crate xmas_elf;
 #[macro_use]
 extern crate fixedvec;
+extern crate font8x8;
 
 use bootloader::bootinfo::BootInfo;
 use core::panic::PanicInfo;
@@ -32,6 +33,11 @@ global_asm!(include_str!("stage_3.s"));
 global_asm!(include_str!("stage_4.s"));
 global_asm!(include_str!("context_switch.s"));
 
+#[cfg(feature = "vga_320x200")]
+global_asm!(include_str!("video_mode/vga_320x200.s"));
+#[cfg(not(feature = "vga_320x200"))]
+global_asm!(include_str!("video_mode/vga_text_80x25.s"));
+
 extern "C" {
     fn context_switch(boot_info: VirtAddr, entry_point: VirtAddr, stack_pointer: VirtAddr) -> !;
 }

src/main.rs

@@ -0,0 +1,8 @@
+#[cfg(not(feature = "vga_320x200"))]
+pub use self::vga_text_80x25::*;
+
+#[cfg(feature = "vga_320x200")]
+pub use self::vga_320x200::*;
+
+mod vga_text_80x25;
+mod vga_320x200;

src/printer/mod.rs

@@ -0,0 +1,81 @@
+use core::fmt::{Result, Write};
+use core::slice;
+use core::sync::atomic::{AtomicUsize, Ordering};
+
+const VGA_BUFFER: *mut u8 = 0xa0000 as *mut _;
+const SCREEN_WIDTH: usize = 320;
+const SCREEN_HEIGHT: usize = 200;
+
+pub static X_POS: AtomicUsize = AtomicUsize::new(1); // must not be 0 so that we don't have a .bss section
+pub static Y_POS: AtomicUsize = AtomicUsize::new(1); // must not be 0 so that we don't have a .bss section
+
+pub struct Printer;
+
+impl Printer {
+    pub fn clear_screen(&mut self) {
+        let vga_buffer = Self::vga_buffer();
+        for byte in vga_buffer {
+            *byte = 0x00;
+        }
+        X_POS.store(0, Ordering::SeqCst);
+        Y_POS.store(0, Ordering::SeqCst);
+    }
+
+    fn vga_buffer() -> &'static mut [u8] {
+        unsafe { slice::from_raw_parts_mut(VGA_BUFFER, SCREEN_WIDTH * SCREEN_HEIGHT) }
+    }
+
+    fn newline(&mut self) {
+        let y_pos = Y_POS.fetch_add(8, Ordering::SeqCst);
+        X_POS.store(0, Ordering::SeqCst);
+        if y_pos >= SCREEN_HEIGHT {
+            self.clear_screen();
+        }
+    }
+
+    fn write_char(&mut self, c: char) {
+        use font8x8::{self, UnicodeFonts};
+
+        if c == '\n' {
+            self.newline();
+            return;
+        }
+
+        let vga_buffer = Self::vga_buffer();
+
+        let x_pos = X_POS.fetch_add(8, Ordering::SeqCst);
+        let y_pos = Y_POS.load(Ordering::SeqCst);
+
+        match c {
+            ' '..='~' => {
+                let rendered = font8x8::BASIC_FONTS
+                    .get(c)
+                    .expect("character not found in basic font");
+                for (y, byte) in rendered.iter().enumerate() {
+                    for (x, bit) in (0..8).enumerate() {
+                        if *byte & (1 << bit) == 0 {
+                            continue
+                        }
+                        let color = 0xf;
+                        vga_buffer[(y_pos + y) * SCREEN_WIDTH + x_pos + x] = color;
+                    }
+                }
+            }
+            _ => panic!("unprintable character"),
+        }
+
+        if x_pos + 8 >= SCREEN_WIDTH {
+            self.newline();
+        }
+    }
+}
+
+impl Write for Printer {
+    fn write_str(&mut self, s: &str) -> Result {
+        for c in s.chars() {
+            self.write_char(c);
+        }
+
+        Ok(())
+    }
+}

src/printer/vga_320x200.rs

@@ -182,7 +182,6 @@ rest_of_bootloader_load_failed:
 
 boot_start_str: .asciz "Booting (first stage)..."
 error_str: .asciz "Error: "
-no_cpuid_str: .asciz "No CPUID support"
 no_int13h_extensions_str: .asciz "No support for int13h extensions"
 rest_of_bootloader_load_failed_str: .asciz "Failed to load rest of bootloader"
 

src/printer.rs renamed to src/printer/vga_text_80x25.rs

@@ -86,6 +86,9 @@ create_memory_map:
     lea di, es:[_memory_map]
     call do_e820
 
+video_mode_config:
+    call config_video_mode
+
 enter_protected_mode_again:
     cli
     lgdt [gdt32info]

src/stage_1.s

@@ -13,17 +13,8 @@ stage_3:
     mov es, bx # set extra segment
     mov ss, bx # set stack segment
 
-    # print "3rd stage" to the top right
-    mov eax, 0x0f720f33 # "3r"
-    mov [0xb808c], eax
-    mov eax, 0x0f200f64 # "d "
-    mov [0xb808c + 4], eax
-    mov eax, 0x0f740f73 # "st"
-    mov [0xb808c + 8], eax
-    mov eax, 0x0f670f61 # "ag"
-    mov [0xb808c + 12], eax
-    mov eax, 0x0f200f65 # "e "
-    mov [0xb808c + 16], eax
+    lea si, boot_third_stage_str
+    call vga_println
 
 check_cpu:
     call check_cpuid
@@ -86,13 +77,8 @@ set_up_page_tables:
     add ecx, 1
     cmp ecx, edx
     jb map_p1_table
-    #
-    map_vga_buffer:
-    mov eax, 0xb8000
-    or eax, (1 | 2)
-    mov ecx, 0xb8000
-    shr ecx, 12
-    mov [_p1 + ecx * 8], eax
+    map_framebuffer:
+    call vga_map_frame_buffer
 
 enable_paging:
     # Write back cache and add a memory fence. I'm not sure if this is
@@ -165,15 +151,8 @@ check_cpuid:
     je no_cpuid
     ret
 no_cpuid:
-    # print "no cpuid" to the top right
-    mov eax, 0x4f6f4f6e # "no"
-    mov [0xb8130], eax
-    mov eax, 0x4f634f20 # " c"
-    mov [0xb8130 + 4], eax
-    mov eax, 0x4f754f70 # "pu"
-    mov [0xb8130 + 8], eax
-    mov eax, 0x4f644f69 # "id"
-    mov [0xb8130 + 12], eax
+    lea esi, no_cpuid_str
+    call vga_println
 no_cpuid_spin:
     hlt
     jmp no_cpuid_spin
@@ -192,19 +171,8 @@ check_long_mode:
     jz no_long_mode        # If it's not set, there is no long mode
     ret
 no_long_mode:
-    # print "no long mode" to the top right
-    mov eax, 0x4f6f4f6e # "no"
-    mov [0xb8128], eax
-    mov eax, 0x4f6c4f20 # " l"
-    mov [0xb8128 + 4], eax
-    mov eax, 0x4f6e4f6f # "on"
-    mov [0xb8128 + 8], eax
-    mov eax, 0x4f204f67 # "g "
-    mov [0xb8128 + 12], eax
-    mov eax, 0x4f6f4f6d # "mo"
-    mov [0xb8128 + 16], eax
-    mov eax, 0x4f654f64 # "de"
-    mov [0xb8128 + 20], eax
+    lea esi, no_long_mode_str
+    call vga_println
 no_long_mode_spin:
     hlt
     jmp no_long_mode_spin
@@ -226,3 +194,7 @@ gdt_64:
 gdt_64_pointer:
     .word gdt_64_pointer - gdt_64 - 1    # 16-bit Size (Limit) of GDT.
     .long gdt_64                            # 32-bit Base Address of GDT. (CPU will zero extend to 64-bit)
+
+boot_third_stage_str: .asciz "Booting (third stage)..."
+no_cpuid_str: .asciz "Error: CPU does not support CPUID"
+no_long_mode_str: .asciz "Error: CPU does not support long mode"

src/stage_2.s

@@ -0,0 +1,90 @@
+.section .boot, "awx"
+.intel_syntax noprefix
+.code16
+
+config_video_mode:
+    mov ah, 0
+    mov al, 0x13 # 320x200 256 color graphics
+    int 0x10
+    ret
+
+.code32
+
+vga_map_frame_buffer:
+    mov eax, 0xa0000
+    or eax, (1 | 2)
+vga_map_frame_buffer_loop:
+    mov ecx, eax
+    shr ecx, 12
+    mov [_p1 + ecx * 8], eax
+
+    add eax, 4096
+    cmp eax, 0xa0000 + 320 * 200
+    jl vga_map_frame_buffer_loop
+
+    ret
+
+# print a string and a newline
+# IN
+#   esi: points at zero-terminated String
+vga_println:
+    push eax
+    push ebx
+    push ecx
+    push edx
+
+    call vga_print
+
+    # newline
+    mov edx, 0
+    mov eax, vga_position
+    mov ecx, 80 * 2
+    div ecx
+    add eax, 1
+    mul ecx
+    mov vga_position, eax
+
+    pop edx
+    pop ebx
+    pop ecx
+    pop eax
+
+    ret
+
+# print a string
+# IN
+#   esi: points at zero-terminated String
+# CLOBBER
+#   ah, ebx
+vga_print:
+    cld
+vga_print_loop:
+    # note: if direction flag is set (via std)
+    # this will DECREMENT the ptr, effectively
+    # reading/printing in reverse.
+    lodsb al, BYTE PTR [esi]
+    test al, al
+    jz vga_print_done
+    call vga_print_char
+    jmp vga_print_loop
+vga_print_done:
+    ret
+
+
+# print a character
+# IN
+#   al: character to print
+# CLOBBER
+#   ah, ebx
+vga_print_char:
+    mov ebx, vga_position
+    mov ah, 0x0f
+    mov [ebx + 0xa0000], ax
+
+    add ebx, 2
+    mov [vga_position], ebx
+
+    ret
+
+vga_position:
+    .double 0