4 files changed, 115 insertions, 1 deletions
diff --git a/mubios/core/post.c b/mubios/core/post.c
index a37f192..076d262 100644
--- a/mubios/core/post.c
+++ b/mubios/core/post.c
@@ -36,5 +36,14 @@ post_main (void)
   pit_init ();
   ioapic_init ();
 
-  serial_write ("mubios: IVT/PIC/PIT initialized\r\n");
+  volatile u8 *mbr;
+  u8 ata_status;
+
+  mbr = (volatile u8 *)0x00007C00u;
+  ata_status = ata_read_sector28 (0, (u16 *)mbr);
+
+  if (ata_status == 0 && mbr[0x01FE] == 0x55 && mbr[0x01FF] == 0xAA)
+    serial_write ("mubios: MBR loaded\r\n");
+  else
+    serial_write ("mubios: MBR read failed\r\n");
 }
diff --git a/mubios/drivers/ata.c b/mubios/drivers/ata.c
new file mode 100644
index 0000000..a0cd12a
--- /dev/null
+++ b/mubios/drivers/ata.c
@@ -0,0 +1,93 @@
+/*
+ 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 ATA_DATA 0x1F0u
+#define ATA_SECTOR_COUNT 0x1F2u
+#define ATA_LBA_LOW 0x1F3u
+#define ATA_LBA_MID 0x1F4u
+#define ATA_LBA_HIGH 0x1F5u
+#define ATA_DRIVE 0x1F6u
+#define ATA_STATUS 0x1F7u
+#define ATA_COMMAND 0x1F7u
+
+#define ATA_STATUS_ERR 0x01u
+#define ATA_STATUS_DRQ 0x08u
+#define ATA_STATUS_BSY 0x80u
+
+#define ATA_CMD_READ_SECTORS 0x20u
+
+static u8
+ata_wait_not_busy (void)
+{
+  u8 status;
+
+  do
+    {
+      status = io_in8 (ATA_STATUS);
+    }
+  while ((status & ATA_STATUS_BSY) != 0);
+
+  return status;
+}
+
+static void
+ata_delay_400ns (void)
+{
+  io_in8 (ATA_STATUS);
+  io_in8 (ATA_STATUS);
+  io_in8 (ATA_STATUS);
+  io_in8 (ATA_STATUS);
+}
+
+u8
+ata_read_sector28 (u32 lba, u16 *buffer)
+{
+  u8 status;
+  u16 index;
+
+  status = ata_wait_not_busy ();
+  if ((status & ATA_STATUS_ERR) != 0)
+    return 1;
+
+  io_out8 (ATA_DRIVE, (u8)(0xE0u | ((lba >> 24) & 0x0Fu)));
+  ata_delay_400ns ();
+
+  io_out8 (ATA_SECTOR_COUNT, 1);
+  io_out8 (ATA_LBA_LOW, (u8)(lba & 0xFFu));
+  io_out8 (ATA_LBA_MID, (u8)((lba >> 8) & 0xFFu));
+  io_out8 (ATA_LBA_HIGH, (u8)((lba >> 16) & 0xFFu));
+  io_out8 (ATA_COMMAND, ATA_CMD_READ_SECTORS);
+
+  status = ata_wait_not_busy ();
+  if ((status & ATA_STATUS_ERR) != 0)
+    return 1;
+
+  if ((status & ATA_STATUS_DRQ) == 0)
+    return 1;
+
+  for (index = 0; index < 256; ++index)
+    buffer[index] = io_in16 (ATA_DATA);
+
+  return 0;
+}
diff --git a/mubios/include/bios.h b/mubios/include/bios.h
index eee22e8..7d2d447 100644
--- a/mubios/include/bios.h
+++ b/mubios/include/bios.h
@@ -50,4 +50,6 @@ void ioapic_init (void);
 
 void ivt_init (void);
 
+u8 ata_read_sector28 (u32 lba, u16 *buffer);
+
 #endif // MUBIOS_BIOS_H
diff --git a/mubios/include/io.h b/mubios/include/io.h
index 8b50508..cedd1c1 100644
--- a/mubios/include/io.h
+++ b/mubios/include/io.h
@@ -40,4 +40,14 @@ io_in8 (u16 port)
   return value;
 }
 
+static inline u16
+io_in16 (u16 port)
+{
+  u16 value;
+
+  __asm__ volatile ("inw %1, %0" : "=a"(value) : "dN"(port));
+
+  return value;
+}
+
 #endif // MUBIOS_IO_H