basic os stuff

.gitignore

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+CLAUDE.md
+*.err

Makefile

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+# -------------------------------------------------------
+# Real Mode OS Makefile
+# Tools: NASM, OpenWatcom (wcc/wlink), QEMU
+# -------------------------------------------------------
+
+# Tools
+NASM        := nasm
+WCC         := wcc
+WLINK       := wlink
+QEMU        := qemu-system-i386
+DD          := dd
+
+# Flags
+NASM_BIN    := -f bin
+NASM_OBJ    := -f obj
+WCC_FLAGS   := -ms -0 -wx -s -ecc   # small model, 8086, warnings, no stack check, cdecl
+QEMU_FLAGS   = -fda $(IMG) -monitor stdio
+
+# Output names
+BOOT_SRC    := boot.asm
+ENTRY_SRC   := entry.asm
+KMAIN_SRC   := kmain.c
+LINK_FILE   := kernel.lnk
+
+BOOT_BIN    := bootloader.bin
+ENTRY_OBJ   := entry.obj
+KMAIN_OBJ   := kmain.obj
+KERNEL_BIN  := kernel.bin
+IMG         := floppy.img
+
+BIOS_SRC := bios.asm
+BIOS_OBJ := bios.obj
+
+
+
+# -------------------------------------------------------
+# Default target
+# -------------------------------------------------------
+.PHONY: all clean run debug
+
+all: $(IMG)
+
+# -------------------------------------------------------
+# Bootloader — flat binary
+# -------------------------------------------------------
+$(BOOT_BIN): $(BOOT_SRC)
+	$(NASM) $(NASM_BIN) $< -o $@
+
+# -------------------------------------------------------
+# Kernel entry point — OMF object
+# -------------------------------------------------------
+$(ENTRY_OBJ): $(ENTRY_SRC)
+	$(NASM) $(NASM_OBJ) $< -o $@
+
+# -------------------------------------------------------
+# C kernel — OMF object via OpenWatcom
+# -------------------------------------------------------
+$(KMAIN_OBJ): $(KMAIN_SRC)
+	$(WCC) $< $(WCC_FLAGS) -fo=$@
+
+$(BIOS_OBJ): $(BIOS_SRC)
+	$(NASM) $(NASM_OBJ) $< -o $@
+
+$(KERNEL_BIN): $(ENTRY_OBJ) $(BIOS_OBJ) $(KMAIN_OBJ) $(LINK_FILE)
+	$(WLINK) @$(LINK_FILE)
+
+# -------------------------------------------------------
+# Floppy image
+# -------------------------------------------------------
+$(IMG): $(BOOT_BIN) $(KERNEL_BIN)
+	$(DD) if=/dev/zero    of=$@          bs=512 count=2880
+	$(DD) if=$(BOOT_BIN)  of=$@ conv=notrunc
+	$(DD) if=$(KERNEL_BIN) of=$@ seek=1 conv=notrunc bs=512
+
+# -------------------------------------------------------
+# Run in QEMU
+# -------------------------------------------------------
+run: $(IMG)
+	$(QEMU) $(QEMU_FLAGS)
+
+# -------------------------------------------------------
+# Debug — QEMU with GDB stub and interrupt logging
+# -------------------------------------------------------
+debug: $(IMG)
+	$(QEMU) $(QEMU_FLAGS) \
+		-s -S \
+		-d int \
+		-D qemu.log
+
+# -------------------------------------------------------
+# Clean
+# -------------------------------------------------------
+clean:
+	rm -f $(BOOT_BIN) $(ENTRY_OBJ) $(KMAIN_OBJ) $(KERNEL_BIN) $(IMG) $(BIOS_OBJ)\
+	      kernel.map qemu.log

bios.asm

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+[BITS 16]
+
+  global _print_char
+  global _get_char
+  global _check_key
+  global _set_cursor
+   global _get_cursor_pos
+    global _set_cursor_pos
+  segment _TEXT class=CODE
+
+  _print_char:
+      push bp
+      mov  bp, sp
+      mov  ah, 0x0E       ; BIOS TTY write
+      mov  al, [bp+4]     ; first arg: char c
+      xor  bh, bh         ; page 0
+      int  0x10
+      pop  bp
+      ret
+_get_char:
+          ; Returns: AL = ASCII char, AH = scancode
+          ; Blocks until a key is pressed
+          xor ah, ah                  ; Function 0: wait for keypress
+          int 0x16
+          xor ah, ah
+          ret
+
+_check_key:
+          ; Non-blocking: returns ZF=1 if no key waiting
+          mov ah, 0x01                ; Function 1: check buffer
+          int 0x16
+          jz .empty
+          mov ax, 1
+          ret                         ; ZF=0 means key available, AL/AH = key
+    .empty:
+    xor ax, ax
+    ret
+_set_cursor:
+    mov ah, 0x01
+    mov cx, 0x0607
+    ret
+_get_cursor_pos:
+          mov  ah, 0x03
+          xor  bh, bh
+          int  0x10           ; DH = row, DL = col
+          mov  ax, dx         ; DH->AH, DL->AL in one shot
+          ret
+
+_set_cursor_pos:
+                push bp
+                mov  bp, sp
+                mov  ah, 0x02       ; AH=02h: set cursor position
+                xor  bh, bh         ; page 0
+                mov  dh, [bp+4]     ; row
+                mov  dl, [bp+6]     ; col
+                int  0x10
+                pop  bp
+                ret

boot.asm

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+[BITS 16]
+[ORG 0x7C00]
+
+KERNEL_SEGMENT equ 0x1000
+KERNEL_SECTORS equ 32
+boot:
+jmp 0x0000: .init
+.init:
+cli
+xor ax,ax
+mov ds,ax
+mov es, ax
+mov ss, ax
+mov sp, 0x7C00
+sti
+
+mov [boot_drive], dl
+xor ax,ax
+int 0x13
+
+jc .disk_error
+
+call load_kernel
+
+mov ax, KERNEL_SEGMENT
+mov ds, ax
+mov es, ax
+
+jmp KERNEL_SEGMENT:0x0000
+
+.disk_error:
+mov si, disk_err
+call print_str
+cli
+hlt
+load_kernel:
+mov ax, KERNEL_SEGMENT
+mov es,ax
+xor bx, bx
+
+mov ah, 0x02
+mov al, KERNEL_SECTORS
+mov ch, 0
+mov cl, 2
+mov dh, 0
+mov dl, [boot_drive]
+int 0x13
+jc .disk_error
+ret
+.disk_error:
+mov si, disk_err
+call print_str
+cli
+hlt
+
+
+print_str:
+lodsb
+or al, al
+jz .done
+mov ah, 0x0E
+int 0x10
+jmp print_str
+.done:
+ret
+
+boot_drive: db 0
+disk_err: db "Disk error", 0x0D, 0X0A, 0
+times 510 - ($-$$) db 0
+dw 0xAA55

entry.asm

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+[BITS 16]
+
+
+
+extern _kmain
+
+global kernel_entry
+global _small_code_             ; Watcom small model expects this
+
+segment _TEXT class=CODE
+
+_small_code_:                   ; Must be at start of CODE segment
+kernel_entry:
+    cli
+    mov ax, 0x1000
+    mov ds, ax
+    mov es, ax
+    mov ss, ax
+    mov sp, 0x7000              ; Just use a fixed address for stack
+    xor bp, bp
+    sti
+    call _kmain
+.halt:
+cli
+hlt
+jmp .halt
+segment _BSS class=BSS
+    resb 4096

kernel.lnk

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+FORMAT RAW BIN
+ORDER CLNAME CODE CLNAME DATA CLNAME BSS
+OPTION OFFSET=0x0000
+OPTION MAP=kernel.map
+OPTION STACK=4096
+OPTION NODEFAULTLIBS
+FILE entry.obj
+FILE bios.obj
+FILE kmain.obj
+NAME kernel.bin

kmain.c

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+#define BUF_SIZE 64
+#define HEAP_SIZE 8192
+static char heap[HEAP_SIZE];
+static int  heap_top = 0;
+
+void* kmalloc(int size) {
+    void* ptr;
+    if (heap_top + size > HEAP_SIZE) return 0;
+    ptr = &heap[heap_top];
+    heap_top += size;
+    return ptr;
+}
+void print_char(char c);
+char get_char(void);
+int  check_key(void);
+void set_cursor(void);
+void set_cursor_pos(char row, char col);
+int get_cursor_pos();
+int str_eq(char* a, char* b) {
+      int i = 0;
+      while (a[i] && b[i]) {
+          if (a[i] != b[i]) return 0;
+          i++;
+      }
+      return a[i] == b[i];
+  }
+void print_string(char* str){
+    int i = 0;
+    while (str[i] != '\0'){
+        print_char(str[i]);
+        i++;
+    }
+}
+void print_hex(unsigned int n) {
+      char hex[] = "0x0000";
+      int i;
+      int nibble;
+      for (i = 5; i >= 2; i--) {
+          nibble = n & 0xF;
+          hex[i] = nibble < 10 ? '0' + nibble : 'A' + nibble - 10;
+          n >>= 4;
+      }
+      print_string(hex);
+  }
+
+
+ void read_line(char* buf) {
+     int i = 0;
+     char c;
+     while (i < BUF_SIZE - 1) {
+         c = get_char();
+         if (c == '\r') break;        /* Enter */
+         if (c == '\b' && i > 0) {   /* Backspace */
+             i--;
+             print_char('\b');
+             print_char(' ');
+             print_char('\b');
+         } else {
+             buf[i++] = c;
+             print_char(c);           /* echo */
+         }
+     }
+     buf[i] = '\0';
+ }
+ void kmain(void) {
+      char buf[BUF_SIZE];
+      set_cursor();
+      print_string("senkOS> ");
+      while (1) {
+          read_line(buf);
+          print_char('\n');
+          if (str_eq(buf, "hello")) {
+              print_string("world\n");
+          } else {
+              print_string("unknown command\n");
+          }
+          print_string("senkOS> ");
+      }
+  }