1 files changed, 106 insertions, 0 deletions
diff --git a/x86-bare-metal/mbr-pure-zig/mbr.zig b/x86-bare-metal/mbr-pure-zig/mbr.zig
new file mode 100644
index 0000000..666aa6b
--- /dev/null
+++ b/x86-bare-metal/mbr-pure-zig/mbr.zig
@@ -0,0 +1,106 @@
+const bios = @import("bios.zig");
+
+// -- ENTRY POINT ---------------------------------------------------------------
+
+export fn _entry() linksection(".boot") callconv(.naked) noreturn {
+    asm volatile (
+    // Disable interrupts.
+        \\cli
+        // Clear segment selectors.
+        \\xor %%ax, %%ax
+        \\mov %%ax, %%ds
+        \\mov %%ax, %%es
+        \\mov %%ax, %%ss
+        \\mov %%ax, %%fs
+        \\mov %%ax, %%gs
+        \\mov $0x7c00, %sp
+        // Long jump to set cs to 0x0000, as some BIOSes load the MBR
+        // to either 07c0:0000 or 0000:7c000.
+        \\ljmp $0x0, $main
+    );
+}
+
+// -- MAIN ----------------------------------------------------------------------
+
+// main should be "callconv(.naked)", once issue is fixed.
+// https://github.com/ziglang/zig/issues/18183
+export fn main() noreturn {
+    for (0..255) |i| {
+        if (i < bios.ROWS) {
+            bios.set_pos(@truncate(i));
+        } else {
+            // Once we reach the bottom of the screen start scrolling.
+            bios.scroll_up();
+            bios.set_pos(bios.ROWS - 1);
+        }
+        puts_dec(i + 1);
+        bios.putc(' ');
+        puts_hex(i + 1);
+        bios.putc(' ');
+        bios.putc(@truncate('a' + (i % 26)));
+        bios.putc(@truncate('a' + (i % 26)));
+        waste_time();
+    }
+    puts("\ndone");
+
+    while (true) {
+        asm volatile ("hlt");
+    }
+}
+
+// -- UTILS ---------------------------------------------------------------------
+
+fn puts(str: []const u8) void {
+    for (str) |c| {
+        bios.putc(c);
+    }
+}
+
+fn puts_dec(init_val: u32) void {
+    var val = init_val;
+    var buf: [32]u8 = undefined;
+    var idx = buf.len;
+
+    while (val > 0 and idx != 0) : (val /= 10) {
+        idx -= 1;
+        buf[idx] = @as(u8, @truncate(val % 10)) + '0';
+    }
+    puts(buf[idx..]);
+}
+
+fn puts_hex(init_val: u32) void {
+    var val = init_val;
+    var buf: [32]u8 = undefined;
+    var idx = buf.len;
+
+    while (val > 0 and idx != 0) : (val /= 16) {
+        idx -= 1;
+        const digit = switch (@as(u8, @truncate(val % 16))) {
+            0...9 => |d| '0' + d,
+            10...15 => |d| 'a' + d - 10,
+            else => '?',
+        };
+        buf[idx] = digit;
+    }
+    puts(buf[idx..]);
+}
+
+fn rdtsc() u32 {
+    return asm volatile ("rdtsc"
+        : [eax] "={eax}" (-> u32),
+        :
+        : "edx"
+    );
+}
+
+fn waste_time() void {
+    const start = rdtsc();
+    var now = start;
+    var idx: usize = 0;
+    while (now - start < (1 << 28)) : (idx += 1) {
+        if (idx == 10_000) {
+            now = rdtsc();
+            idx = 0;
+        }
+    }
+}