From 75f21a5124cc4ed542c8faff64a36c68bb7fbe57 Mon Sep 17 00:00:00 2001
From: Richard Qin <richard.qin.x@gmail.com>
Date: Sun, 8 Nov 2026 04:34:02 +0800
Subject: [mubios] Create 16-bit entry points for IRQ0/IRQ1 and install the IVT
 vectors.

Signed-off-by: Richard Qin <richard.qin.x@gmail.com>
---
 mubios/arch/irq.S     | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 mubios/core/bda.c     | 32 ++++++++++++++++++++++++++++++++
 mubios/core/post.c    |  4 +++-
 mubios/include/bios.h |  2 ++
 mubios/linker.ld      |  4 ++++
 5 files changed, 92 insertions(+), 1 deletion(-)
 create mode 100644 mubios/arch/irq.S

diff --git a/mubios/arch/irq.S b/mubios/arch/irq.S
new file mode 100644
index 0000000..6eea350
--- /dev/null
+++ b/mubios/arch/irq.S
@@ -0,0 +1,51 @@
+# 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/>.
+
+	.intel_syntax noprefix
+	.code16
+
+	.section .text16.irq, "ax"
+
+	.global irq0_entry
+	.type irq0_entry, @function
+
+irq0_entry:
+	push ax
+
+	# Acknowledge IRQ0 on the master PIC.
+	mov al, 0x20
+	out 0x20, al
+
+	pop ax
+	iret
+
+	.global irq1_entry
+	.type irq1_entry, @function
+
+irq1_entry:
+	push ax
+
+	# Read the PS/2 scan code before sending EOI.
+	in al, 0x60
+
+	mov al, 0x20
+	out 0x20, al
+
+	pop ax
+	iret
diff --git a/mubios/core/bda.c b/mubios/core/bda.c
index d626963..c2ecfb1 100644
--- a/mubios/core/bda.c
+++ b/mubios/core/bda.c
@@ -45,3 +45,35 @@ bda_init (void)
 
   store_u16 (bda + BDA_CONVENTIONAL_MEMORY_OFFSET, (u16)(ebda_base >> 10));
 }
+
+struct ivt_entry
+{
+  u16 offset;
+  u16 segment;
+};
+
+extern u8 __rom_start[];
+extern void irq0_entry (void);
+extern void irq1_entry (void);
+
+static void
+install_ivt_entry (u8 vector, void (*handler) (void))
+{
+  volatile struct ivt_entry *ivt;
+  u32 rom_base;
+  u32 handler_address;
+
+  ivt = (volatile struct ivt_entry *)MUBIOS_IVT_BASE;
+  rom_base = (u32)__rom_start;
+  handler_address = (u32)handler;
+
+  ivt[vector].offset = (u16)(handler_address - rom_base);
+  ivt[vector].segment = (u16)(rom_base >> 4);
+}
+
+void
+ivt_init (void)
+{
+  install_ivt_entry (0x08u, irq0_entry);
+  install_ivt_entry (0x09u, irq1_entry);
+}
diff --git a/mubios/core/post.c b/mubios/core/post.c
index afad12b..34ee715 100644
--- a/mubios/core/post.c
+++ b/mubios/core/post.c
@@ -30,8 +30,10 @@ post_main (void)
   memory_init ();
   bda_init ();
 
+  ivt_init();
+
   pic_init ();
   pit_init ();
 
-  serial_write ("mubios: PIC/PIT initialized\r\n");
+  serial_write ("mubios: IVT/PIC/PIT initialized\r\n");
 }
diff --git a/mubios/include/bios.h b/mubios/include/bios.h
index 3df9846..e524682 100644
--- a/mubios/include/bios.h
+++ b/mubios/include/bios.h
@@ -47,4 +47,6 @@ void serial_write (const char *text);
 void pic_init (void);
 void pit_init (void);
 
+void ivt_init (void);
+
 #endif // MUBIOS_BIOS_H
diff --git a/mubios/linker.ld b/mubios/linker.ld
index 004c1bc..5dee699 100644
--- a/mubios/linker.ld
+++ b/mubios/linker.ld
@@ -43,6 +43,10 @@ SECTIONS
     {
 	KEEP(*(.text16.mode))
     } > ROM
+    .text16.irq :
+    {
+        KEEP(*(.text16.irq))
+    } > ROM
     .text16 :
     {
 	KEEP(*(.text16.mode))
-- 
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