[mubios] Implement the COM1 serial port driver and POST output.

Signed-off-by: Richard Qin <richard.qin.x@gmail.com>

2 files changed, 47 insertions, 0 deletions

diff --git a/mubios/include/bios.h b/mubios/include/bios.h
index 7681bf0..c3b5026 100644
--- a/mubios/include/bios.h
+++ b/mubios/include/bios.h
@@ -40,4 +40,8 @@ void post_main (void);
 void memory_init (void);
 void bda_init (void);
 
+void serial_init (void);
+void serial_putc (u8 value);
+void serial_write (const char *text);
+
 #endif // MUBIOS_BIOS_H
diff --git a/mubios/include/io.h b/mubios/include/io.h
new file mode 100644
index 0000000..8b50508
--- /dev/null
+++ b/mubios/include/io.h
@@ -0,0 +1,43 @@
+/*
+ RCC-Project
+
+ Copyright (C) 2026 Richard Qin
+
+ This file is part of RCC-Project.
+
+ RCC-Project is free software; you can redistribute it and/or modify it under
+ the terms of the GNU General Public License as published by the Free
+ Software Foundation; either version 3 of the License, or (at your option) any
+ later version.
+
+ RCC-Project is distributed in the hope that it will be useful, but WITHOUT ANY
+ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License along with
+ RCC-Project; see the file COPYING.  If not see
+ <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef MUBIOS_IO_H
+#define MUBIOS_IO_H
+
+#include "bios.h"
+
+static inline void
+io_out8 (u16 port, u8 value)
+{
+  __asm__ volatile ("outb %0, %1" : : "a"(value), "Nd"(port));
+}
+
+static inline u8
+io_in8 (u16 port)
+{
+  u8 value;
+
+  __asm__ volatile ("inb %1, %0" : "=a"(value) : "Nd"(port));
+
+  return value;
+}
+
+#endif // MUBIOS_IO_H