From 6d22fb5b88dc568a8c04946c196a52905b34da0a Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Thu, 11 Dec 2025 03:51:13 +0000
Subject: [PATCH] Initialize NewOS project: Kernel, Build System, and Boot
 Image

- Created `kernel/` structure with assembly entry point and C main loop.
- Implemented basic video driver for Macintosh SE/30 (monochrome framebuffer).
- Added `Makefile` using `m68k-linux-gnu` toolchain.
- Added `tools/create_image.sh` to generate HFS-formatted `boot.img` with custom Boot Blocks.
- Configured environment setup script.
---
 .gitignore             |  6 ++++
 Makefile               | 28 +++++++++++++++++
 include/mac_hardware.h | 29 ++++++++++++++++++
 kernel/head.S          | 40 ++++++++++++++++++++++++
 kernel/main.c          | 27 +++++++++++++++++
 kernel/video.c         | 69 ++++++++++++++++++++++++++++++++++++++++++
 linker.ld              | 22 ++++++++++++++
 tools/create_image.sh  | 42 +++++++++++++++++++++++++
 tools/setup_env.sh     | 16 ++++++++++
 9 files changed, 279 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 include/mac_hardware.h
 create mode 100644 kernel/head.S
 create mode 100644 kernel/main.c
 create mode 100644 kernel/video.c
 create mode 100644 linker.ld
 create mode 100755 tools/create_image.sh
 create mode 100755 tools/setup_env.sh

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..60feb77
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+*.o
+*.elf
+*.bin
+*.img
+kernel/
+boot.img
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..2fa9d81
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,28 @@
+CC = m68k-linux-gnu-gcc
+LD = m68k-linux-gnu-ld
+OBJCOPY = m68k-linux-gnu-objcopy
+
+# Use -fPIC for Position Independent Code since ROM loads us anywhere.
+# -msep-data might be needed if we want separate data segment, but -fPIC is standard.
+CFLAGS = -m68030 -O2 -Wall -fno-builtin -nostdlib -Iinclude -fPIC
+LDFLAGS = -T linker.ld
+
+all: boot.img
+
+kernel.elf: kernel/head.o kernel/main.o kernel/video.o
+	$(LD) $(LDFLAGS) -o $@ $^
+
+kernel.bin: kernel.elf
+	$(OBJCOPY) -O binary $< $@
+
+boot.img: kernel.bin tools/create_image.sh
+	./tools/create_image.sh
+
+clean:
+	rm -f kernel/*.o kernel.elf kernel.bin boot.img
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+%.o: %.S
+	$(CC) $(CFLAGS) -c -o $@ $<
diff --git a/include/mac_hardware.h b/include/mac_hardware.h
new file mode 100644
index 0000000..ac6ff0b
--- /dev/null
+++ b/include/mac_hardware.h
@@ -0,0 +1,29 @@
+#ifndef MAC_HARDWARE_H
+#define MAC_HARDWARE_H
+
+// Type definitions
+typedef unsigned char uint8_t;
+typedef unsigned short uint16_t;
+typedef unsigned int uint32_t;
+typedef int int32_t;
+
+// Mac Low Memory Globals
+// Updated based on SysEqu.a findings
+#define ScrnBase    (*(volatile uint32_t*)0x824)
+// ScreenRow at 0x106? SysEqu.a said 0x106 is ScreenRow.
+// Let's verify. 0x106 seems low. But if SysEqu says so.
+// Wait, 0x106 is often "MemTop"? No, MemTop is 0x108.
+// Let's stick with 0x826 if I can verify it, OR use 0x106 if SysEqu is clear.
+// SysEqu: "ScreenRow EQU $106"
+#define ScreenRow   (*(volatile uint16_t*)0x106)
+#define MemTop      (*(volatile uint32_t*)0x108)
+#define ROMBase     (*(volatile uint32_t*)0x2AE)
+
+// VIA1 Addresses (SE/30)
+#define VIA1_BASE   0x50F00000
+
+// Video parameters
+#define SCREEN_WIDTH  512
+#define SCREEN_HEIGHT 342
+
+#endif
diff --git a/kernel/head.S b/kernel/head.S
new file mode 100644
index 0000000..0fa4307
--- /dev/null
+++ b/kernel/head.S
@@ -0,0 +1,40 @@
+    .global _start
+    .global _halt
+
+    .text
+_start:
+    /*
+     * Boot Block Header (standard Mac)
+     * The first 2 bytes must be 'LK' (0x4C, 0x4B)
+     * The next 2 bytes are a branch to the code.
+     */
+
+    /* Signature 'LK' */
+    .byte 0x4C, 0x4B
+
+    /* Branch to Entry (offset will be calculated by assembler) */
+    bra.w entry_point
+
+    /* Configuration variables (Boot Block structure) */
+    /* 0x04: Entry point for version (unused) */
+    .byte 0x00, 0x00
+    /* 0x06: Version */
+    .byte 0x00, 0x00
+    /* ... Padding to standard boot block header size if needed ... */
+
+entry_point:
+    /* Disable interrupts */
+    ori.w   #0x0700, %sr
+
+    /* Setup Stack - ROM usually provides a stack, but we should be safe */
+    /* Let's use the top of memory minus some buffer. MemTop is at 0x108. */
+    move.l  0x108, %sp
+    sub.l   #0x1000, %sp  /* Leave 4KB buffer */
+
+    /* Call C kernel (using PC-relative BSR or JSR) */
+    /* Since we are -fPIC, we should use bsr if it's close, or load address relative to PC */
+    bsr.w     kernel_main
+
+_halt:
+    stop    #0x2700
+    bra.s   _halt
diff --git a/kernel/main.c b/kernel/main.c
new file mode 100644
index 0000000..6bb102f
--- /dev/null
+++ b/kernel/main.c
@@ -0,0 +1,27 @@
+#include "mac_hardware.h"
+
+extern void clear_screen();
+extern void kprint(const char* str);
+extern void draw_test_pattern();
+
+void kernel_main() {
+    // 1. Initialize Video
+    // (Assuming ScrnBase is valid from ROM)
+
+    // 2. Clear Screen
+    // clear_screen(); // Commented out to avoid clearing if it's already white, let's just draw on top.
+
+    // 3. Print Welcome Message
+    // kprint("Welcome to NewOS");
+
+    // Draw something visible immediately
+    draw_test_pattern();
+
+    // 4. Infinite Loop (Shell Prompt)
+    while (1) {
+        // Blink a pixel or wait for interrupt
+        volatile int i;
+        for (i=0; i<100000; i++);
+        // TODO: Blink cursor
+    }
+}
diff --git a/kernel/video.c b/kernel/video.c
new file mode 100644
index 0000000..70971e2
--- /dev/null
+++ b/kernel/video.c
@@ -0,0 +1,69 @@
+#include "mac_hardware.h"
+
+// Simple 8x8 font bitmap (A subset for "Hello World")
+// Minimal font data would be here. For now, let's just draw blocks or simple lines.
+// Or we can define a very small font.
+
+// 8x8 bitmap for 'A' (example)
+// 00111100
+// 01100110
+// 01100110
+// 01111110
+// 01100110
+// 01100110
+// 00000000
+
+// We need a simple `put_char` function.
+
+void clear_screen() {
+    uint32_t *screen = (uint32_t *)ScrnBase;
+    uint16_t rowBytes = ScreenRow;
+    uint32_t rows = SCREEN_HEIGHT;
+    uint32_t stride = rowBytes / 4; // Stride in 32-bit words
+
+    for (uint32_t y = 0; y < rows; y++) {
+        for (uint32_t x = 0; x < stride; x++) {
+            screen[y * stride + x] = 0x00000000; // White (0 is white on Mac usually? No, 0 is White, 1 is Black)
+            // Wait, standard Mac video is 1 bit per pixel.
+            // 0 = White, 1 = Black usually.
+            // Let's invert it to be sure we see something.
+            // 0xFFFFFFFF = Black bar.
+            // 0xAAAAAAAA = Striped.
+        }
+    }
+}
+
+void draw_test_pattern() {
+    uint32_t *screen = (uint32_t *)ScrnBase;
+    uint16_t rowBytes = ScreenRow;
+
+    // Draw a black line at the top
+    for (int i=0; i < (rowBytes/4) * 10; i++) {
+        screen[i] = 0xFFFFFFFF;
+    }
+}
+
+// Very minimal font rendering (monochrome)
+// x, y are in pixels
+void draw_pixel(int x, int y, int color) {
+    if (x >= SCREEN_WIDTH || y >= SCREEN_HEIGHT) return;
+
+    uint8_t *screen_byte = (uint8_t *)(ScrnBase + (y * ScreenRow) + (x / 8));
+    uint8_t bit = 1 << (7 - (x % 8));
+
+    if (color) {
+        *screen_byte |= bit; // Set bit (Black)
+    } else {
+        *screen_byte &= ~bit; // Clear bit (White)
+    }
+}
+
+// Simple "Bitmap Font" - just hardcoding 'H' 'e' 'l' 'l' 'o' for MVP to save space
+// In a real OS, we'd include a font.h
+const uint8_t FONT_A[8] = {0x3C, 0x66, 0x66, 0x7E, 0x66, 0x66, 0x66, 0x00};
+// We will just implement a "Print String" that draws blocks for now if font is missing.
+
+void kprint(const char* str) {
+    // Placeholder: Draws a pattern to prove code execution
+    draw_test_pattern();
+}
diff --git a/linker.ld b/linker.ld
new file mode 100644
index 0000000..ca9622e
--- /dev/null
+++ b/linker.ld
@@ -0,0 +1,22 @@
+SECTIONS
+{
+    . = 0x00000000; /* Boot Blocks are loaded at a specific address, often relocatable. */
+    /*
+     * However, Mac ROMs often load Boot Blocks into a pointer passed in registers.
+     * Or they might be Position Independent Code (PIC).
+     * We should compile as PIC if possible, or assume an address.
+     * Usually Boot Blocks are loaded at heap or stack.
+     * Safe bet: Compile as PIC (-fPIC).
+     * But for linker script, we can set 0 and use PC-relative addressing.
+     */
+
+    .text : {
+        *(.text)
+    }
+    .data : {
+        *(.data)
+    }
+    .bss : {
+        *(.bss)
+    }
+}
diff --git a/tools/create_image.sh b/tools/create_image.sh
new file mode 100755
index 0000000..fa283b8
--- /dev/null
+++ b/tools/create_image.sh
@@ -0,0 +1,42 @@
+#!/bin/bash
+set -e
+
+echo "Creating boot.img..."
+
+KERNEL_BIN="kernel.bin"
+IMG="boot.img"
+
+if [ ! -f "$KERNEL_BIN" ]; then
+    echo "Error: $KERNEL_BIN not found. Run make first."
+    exit 1
+fi
+
+# 1. Create a blank 1.44MB floppy image
+dd if=/dev/zero of=$IMG bs=1024 count=1440 2>/dev/null
+
+# 2. Format as HFS (Mac ROM expects HFS volume to check for boot blocks)
+# We use 'NewOS' as the volume name.
+hformat -l "NewOS" $IMG > /dev/null
+
+# 3. Install Boot Blocks
+# The Mac ROM looks at the first 1024 bytes (Boot Blocks) of the disk.
+# Even if HFS is present, the boot blocks are in sectors 0 and 1.
+# `hformat` writes a standard boot block. We need to OVERWRITE it with our kernel code.
+#
+# IMPORTANT: The HFS volume header (MDB) is at sector 2 (offset 1024).
+# We MUST NOT overwrite sector 2.
+# Our kernel.bin must be <= 1024 bytes for this method.
+# If it is larger, we would need to write it to a file and have the boot block load it.
+# For MVP (360 bytes), we just overwrite the boot blocks.
+
+KERNEL_SIZE=$(stat -c%s "$KERNEL_BIN")
+if [ "$KERNEL_SIZE" -gt 1024 ]; then
+    echo "Error: Kernel size ($KERNEL_SIZE bytes) exceeds Boot Block limit (1024 bytes)."
+    echo "This MVP requires the kernel to fit in the boot blocks."
+    exit 1
+fi
+
+# Write our kernel over the first 1024 bytes (preserving the rest of the disk)
+dd if=$KERNEL_BIN of=$IMG conv=notrunc bs=1024 count=1 2>/dev/null
+
+echo "Done. $IMG is ready (HFS formatted with custom Boot Blocks)."
diff --git a/tools/setup_env.sh b/tools/setup_env.sh
new file mode 100755
index 0000000..eb271c5
--- /dev/null
+++ b/tools/setup_env.sh
@@ -0,0 +1,16 @@
+#!/bin/bash
+set -e
+
+# Update package list
+sudo apt-get update
+
+# Install m68k cross-compiler (Linux target is close enough for bare metal if we use -nostdlib)
+sudo apt-get install -y gcc-m68k-linux-gnu binutils-m68k-linux-gnu make
+
+# Install HFS utilities for disk image manipulation
+sudo apt-get install -y hfsutils hfsplus
+
+# Install hex editor for debugging (optional)
+# sudo apt-get install -y hexedit
+
+echo "Environment setup complete."