From 20a854354918735c3289c5576a28fad18ca21757 Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Mon, 21 Apr 2025 22:32:52 +0200
Subject: mbr: add serial port (com) example

---
 x86-bare-metal/mbr-com-serial/mbr.zig | 50 +++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 x86-bare-metal/mbr-com-serial/mbr.zig

(limited to 'x86-bare-metal/mbr-com-serial/mbr.zig')

diff --git a/x86-bare-metal/mbr-com-serial/mbr.zig b/x86-bare-metal/mbr-com-serial/mbr.zig
new file mode 100644
index 0000000..6c6fb77
--- /dev/null
+++ b/x86-bare-metal/mbr-com-serial/mbr.zig
@@ -0,0 +1,50 @@
+const Com = @import("com.zig").Com;
+
+// -- 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 ----------------------------------------------------------------------
+
+// Global access to COM0.
+var com0: ?Com = null;
+
+// main should be "callconv(.naked)", once issue is fixed.
+// https://github.com/ziglang/zig/issues/18183
+export fn main() noreturn {
+    com0 = com0 orelse Com.init(Com.COM1);
+    com0.?.puts("\n\nBooted into mbr.zig\n");
+
+    @panic("end reached, crashing kernel");
+}
+
+pub const panic = @import("std").debug.FullPanic(panicHandler);
+
+fn panicHandler(msg: []const u8, first_trace_addr: ?usize) noreturn {
+    _ = first_trace_addr;
+
+    com0 = com0 orelse Com.init(Com.COM1);
+    com0.?.puts("\nPANIC: ");
+    com0.?.puts(msg);
+    com0.?.puts("\n");
+
+    while (true) {
+        asm volatile ("hlt");
+    }
+}
-- 
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