From 3f0691017ebc861c734a8bb589a11ec4da7d9d95 Mon Sep 17 00:00:00 2001
From: Richard Qin <richard.qin.x@gmail.com>
Date: Sun, 8 Nov 2026 03:53:30 +0800
Subject: [mubios] Implement the COM1 serial port driver and POST output.

Signed-off-by: Richard Qin <richard.qin.x@gmail.com>
---
 mubios/drivers/serial.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 mubios/drivers/serial.c

(limited to 'mubios/drivers/serial.c')

diff --git a/mubios/drivers/serial.c b/mubios/drivers/serial.c
new file mode 100644
index 0000000..3da2093
--- /dev/null
+++ b/mubios/drivers/serial.c
@@ -0,0 +1,99 @@
+/*
+ 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/>.
+ */
+
+#include "bios.h"
+#include "io.h"
+
+#define COM1_BASE 0x03F8u
+
+#define COM_DATA_OFFSET 0x00u
+#define COM_IER_OFFSET 0x01u
+#define COM_FCR_OFFSET 0x02u
+#define COM_LCR_OFFSET 0x03u
+#define COM_MCR_OFFSET 0x04u
+#define COM_LSR_OFFSET 0x05u
+
+#define COM_LCR_DLAB 0x80u
+#define COM_LCR_8N1 0x03u
+
+#define COM_FCR_ENABLE_FIFO 0x01u
+#define COM_FCR_CLEAR_RX 0x02u
+#define COM_FCR_CLEAR_TX 0x04u
+#define COM_FCR_TRIGGER_14 0xC0u
+
+#define COM_MCR_DTR 0x01u
+#define COM_MCR_RTS 0x02u
+#define COM_MCR_OUT2 0x08u
+
+#define COM_LSR_THRE 0x20u
+
+static u16
+com1_port (u16 offset)
+{
+  return (u16)(COM1_BASE + offset);
+}
+
+void
+serial_init (void)
+{
+  // clang-format off
+    io_out8(com1_port(COM_IER_OFFSET), 0x00u);
+
+    io_out8(com1_port(COM_LCR_OFFSET), COM_LCR_DLAB);
+    io_out8(com1_port(COM_DATA_OFFSET), 0x01u);
+    io_out8(com1_port(COM_IER_OFFSET), 0x00u);
+
+    io_out8(com1_port(COM_LCR_OFFSET), COM_LCR_8N1);
+    io_out8(
+        com1_port(COM_FCR_OFFSET),
+        COM_FCR_ENABLE_FIFO |
+        COM_FCR_CLEAR_RX |
+        COM_FCR_CLEAR_TX |
+        COM_FCR_TRIGGER_14
+    );
+    io_out8(
+        com1_port(COM_MCR_OFFSET),
+        COM_MCR_DTR |
+        COM_MCR_RTS |
+        COM_MCR_OUT2
+    );
+  // clang-format on
+}
+
+void
+serial_putc (u8 value)
+{
+  while ((io_in8 (com1_port (COM_LSR_OFFSET)) & COM_LSR_THRE) == 0u)
+    {
+    }
+
+  io_out8 (com1_port (COM_DATA_OFFSET), value);
+}
+
+void
+serial_write (const char *text)
+{
+  while (*text != '\0')
+    {
+      serial_putc ((u8)*text);
+      ++text;
+    }
+}
-- 
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