add lifeboot.asm skel

diff --git a/.gitignore b/.gitignore
index 6e7cfddd48ab97fd23f757bb53696830a7334536..956b27b6eb3a8fde7d9d94ea4518b3701efdf4c5 100644 (file)
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@
 **/*.o
 **/a.out
 prototype
+lifeboot

diff --git a/Makefile b/Makefile
index 9c4db25d4093be94b3e823abeab3a2c98229918b..6ae753483ab480f72f285c912e8426378b8a44f6 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -1,14 +1,20 @@
 SRC_DIR := .
-PROGRAMS := prototype
+PROGRAMS := prototype lifeboot
 CC := gcc
 CFLAGS := -Wall -Wextra -Werror -I.
 
 build: $(PROGRAMS)
 
+lifeboot:
+       nasm lifeboot.asm
+
+run:
+       qemu-system-x86_64 -drive file=lifeboot,format=raw
+
 format:
        find $(SRC_DIR) -iname '*.[hc]' | xargs clang-format -i --style=GNU
 
 clean:
        rm -rf $(PROGRAMS) *.o
 
-.PHONY: build format clean
+.PHONY: build run format clean

diff --git a/lifeboot.asm b/lifeboot.asm
new file mode 100644 (file)
index 0000000..a3b4658
--- /dev/null
+++ b/lifeboot.asm
@@ -0,0 +1,78 @@
+bits 16
+org 0x7c00
+
+%define ORG 0x7c00                  ; where we are loaded initially
+
+%define VGA_SEG 0xb800              ; video memory starts at 0xb8000
+%define VGA_COL 80
+%define VGA_ROW 25
+%define VGA_LENW VGA_COL * VGA_ROW
+
+%define FILL_CHAR 0xfa              ; middle dot
+%define FILL_COLOR 0x04             ; red on black
+%define PRINT_COLOR 0x07            ; grey on black
+
+; entry point -----------------------------------------------------------------
+
+; initialize segment registers
+xor ax, ax
+mov ds, ax
+mov es, ax
+mov ss, ax
+
+; set stack pointers
+mov sp, ORG
+mov bp, ORG
+
+; clear screen ----------------------------------------------------------------
+
+; disable cursor
+mov ch, 0x3f
+mov ah, 0x01
+int 0x10
+
+; clear video memory
+mov cx, VGA_LENW
+mov ax, VGA_SEG
+mov es, ax
+xor di, di
+mov ax, (FILL_COLOR << 8) | FILL_CHAR
+
+rep stosw                   ; fill cx words at es:di with ax
+
+; errors ----------------------------------------------------------------------
+
+hello:
+mov si, str.hello
+
+; print the error message string in si and halt
+; note: we assume es = VGA_SEG and ds = 0
+printerr:
+xor di, di
+mov ah, PRINT_COLOR
+
+; es:di = video memory
+; ds:si = error message
+; al = current char
+; ah = color attribute
+
+write_char:
+lodsb                   ; al = [ds:si], si += 1
+or  al, al              ; on null terminator,
+jz  halt                ;  halt
+stosw                   ; [es:di] = ax, di += 2
+jmp write_char
+
+halt:
+cli                     ; disable interrupts
+hlt
+jmp halt
+
+; data ------------------------------------------------------------------------
+
+str:
+.hello:
+    db "lifeboot", 0
+
+times 510 - ($ - $$) db 0   ; fill remaining bytes with zeroes
+dw 0xaa55                   ; mbr magic byte