[mubios] Initialize IVT, BDA and EBDA.

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

4 files changed, 116 insertions, 2 deletions

diff --git a/mubios/core/bda.c b/mubios/core/bda.c
new file mode 100644
index 0000000..d626963
--- /dev/null
+++ b/mubios/core/bda.c
@@ -0,0 +1,47 @@
+/*
+ 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"
+
+extern u8 __ebda_start[];
+
+static void
+store_u16 (volatile u8 *address, u16 value)
+{
+  address[0] = (u8)(value & 0x00FFu);
+  address[0] = (u8)(value >> 8);
+}
+
+void
+bda_init (void)
+{
+  volatile u8 *bda;
+  u32 ebda_base;
+
+  bda = (volatile u8 *)MUBIOS_BDA_BASE;
+  ebda_base = (u32)__ebda_start;
+
+  store_u16 (bda + BDA_EBDA_SEGMENT_OFFSET, (u16)(ebda_base >> 4));
+
+  store_u16 (bda + BDA_EQUIPMENT_OFFSET, (u16)(ebda_base >> 4));
+
+  store_u16 (bda + BDA_CONVENTIONAL_MEMORY_OFFSET, (u16)(ebda_base >> 10));
+}
diff --git a/mubios/core/memory.c b/mubios/core/memory.c
new file mode 100644
index 0000000..ee7ac43
--- /dev/null
+++ b/mubios/core/memory.c
@@ -0,0 +1,48 @@
+/*
+ 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"
+
+extern u8 __bss_start[];
+extern u8 __bss_end[];
+
+static void
+zero_bytes (volatile u8 *start, volatile u8 *end)
+{
+  volatile u8 *cursor;
+
+  for (cursor = start; cursor < end; ++cursor)
+    {
+      *cursor = 0;
+    }
+}
+
+void
+memory_init (void)
+{
+  zero_bytes ((volatile u8 *)MUBIOS_IVT_BASE,
+              (volatile u8 *)(MUBIOS_IVT_BASE + MUBIOS_IVT_SIZE));
+
+  zero_bytes ((volatile u8 *)MUBIOS_BDA_BASE,
+              (volatile u8 *)(MUBIOS_BDA_BASE + MUBIOS_BDA_SIZE));
+
+  zero_bytes (__bss_start, __bss_end);
+}
diff --git a/mubios/core/post.c b/mubios/core/post.c
index d8ae85c..ec0ddbd 100644
--- a/mubios/core/post.c
+++ b/mubios/core/post.c
@@ -21,6 +21,9 @@
 
 #include "bios.h"
 
-void post_main(void)
+void
+post_main (void)
 {
+  memory_init ();
+  bda_init ();
 }
diff --git a/mubios/include/bios.h b/mubios/include/bios.h
index 1f51244..7681bf0 100644
--- a/mubios/include/bios.h
+++ b/mubios/include/bios.h
@@ -22,6 +22,22 @@
 #ifndef MUBIOS_BIOS_H
 #define MUBIOS_BIOS_H
 
-void post_main(void);
+typedef unsigned char u8;
+typedef unsigned short u16;
+typedef unsigned int u32;
+
+#define MUBIOS_IVT_BASE 0x00000000u
+#define MUBIOS_IVT_SIZE 0x00000400u
+
+#define MUBIOS_BDA_BASE 0x00000400u
+#define MUBIOS_BDA_SIZE 0x00000100u
+
+#define BDA_EBDA_SEGMENT_OFFSET 0x000Eu
+#define BDA_EQUIPMENT_OFFSET 0x0010u
+#define BDA_CONVENTIONAL_MEMORY_OFFSET 0x0013u
+
+void post_main (void);
+void memory_init (void);
+void bda_init (void);
 
 #endif // MUBIOS_BIOS_H