From 91d622ec7eab658ff6704007c2ef1d39c7111281 Mon Sep 17 00:00:00 2001
From: Richard Qin <richard.qin.x@gmail.com>
Date: Sun, 8 Nov 2026 07:20:24 +0800
Subject: [mubios] Add services INT 13h

Signed-off-by: Richard Qin <richard.qin.x@gmail.com>
---
 mubios/services/int13.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)
 create mode 100644 mubios/services/int13.c

diff --git a/mubios/services/int13.c b/mubios/services/int13.c
new file mode 100644
index 0000000..078fa03
--- /dev/null
+++ b/mubios/services/int13.c
@@ -0,0 +1,104 @@
+/*
+ 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 "regs.h"
+
+#define BIOS_CF 0x0001u
+
+struct edd_packet
+{
+  u8 size;
+  u8 reserved;
+  u16 count;
+  u16 buffer_offset;
+  u16 buffer_segment;
+  u32 lba_low;
+  u32 lba_high;
+} __attribute__ ((packed));
+
+static void
+int13_fail (struct bios_regs *regs)
+{
+  regs->ax = 0x0100u;
+  regs->flags |= BIOS_CF;
+}
+
+static struct edd_packet *
+get_edd_packet (struct bios_regs *regs)
+{
+  u32 address;
+
+  address = ((u32)regs->ds << 4) + regs->si;
+  return (struct edd_packet *)address;
+}
+
+void
+int13_service (struct bios_regs *regs)
+{
+  u8 function;
+  struct edd_packet *packet;
+  u32 buffer_address;
+
+  function = (u8)(regs->ax >> 8);
+
+  if (function == 0x41u)
+    {
+      if (regs->bx != 0x55AAu)
+        {
+          int13_fail (regs);
+          return;
+        }
+
+      regs->ax = 0x3000u;
+      regs->bx = 0xAA55u;
+      regs->cx |= 0x0001u;
+      regs->flags &= (u16)~BIOS_CF;
+      return;
+    }
+
+  if (function == 0x42u)
+    {
+      packet = get_edd_packet (regs);
+
+      if (packet->size != 0x10u || packet->count != 1u
+          || packet->lba_high != 0u || packet->lba_low > 0x0FFFFFFFu)
+        {
+          int13_fail (regs);
+          return;
+        }
+
+      buffer_address
+          = ((u32)packet->buffer_segment << 4) + packet->buffer_offset;
+
+      if (ata_read_sector28 (packet->lba_low, (u16 *)buffer_address) != 0)
+        {
+          int13_fail (regs);
+          return;
+        }
+
+      regs->ax = 0;
+      regs->flags &= (u16)~BIOS_CF;
+      return;
+    }
+
+  int13_fail (regs);
+}
-- 
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