[mubios] Implement INT 15h E820h

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

1 files changed, 84 insertions, 0 deletions

diff --git a/mubios/services/int15.c b/mubios/services/int15.c
new file mode 100644
index 0000000..eb66f5c
--- /dev/null
+++ b/mubios/services/int15.c
@@ -0,0 +1,84 @@
+/*
+ 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.
+ */
+
+#include "bios.h"
+#include "regs.h"
+
+#define BIOS_CF 0x0001u
+#define E820_SIGNATURE 0x534D4150u
+#define E820_FUNCTION 0x0000E820u
+#define E820_ENTRY_SIZE 20u
+
+struct e820_entry
+{
+  u32 base_low;
+  u32 base_high;
+  u32 length_low;
+  u32 length_high;
+  u32 type;
+} __attribute__ ((packed));
+
+static const struct e820_entry e820_map[]
+    = { { 0x00000000u, 0x00000000u, 0x0009C000u, 0x00000000u, 1u },
+        { 0x0009C000u, 0x00000000u, 0x00004000u, 0x00000000u, 2u },
+        { 0x000A0000u, 0x00000000u, 0x00060000u, 0x00000000u, 2u },
+        { 0x00100000u, 0x00000000u, 0x07F00000u, 0x00000000u, 1u } };
+
+#define E820_ENTRY_COUNT ((u32)(sizeof (e820_map) / sizeof (e820_map[0])))
+
+static void
+int15_fail (struct bios_regs *regs)
+{
+  regs->eax = 0x8600u;
+  regs->flags |= BIOS_CF;
+}
+
+void
+int15_service (struct bios_regs *regs)
+{
+  struct e820_entry *output;
+  u32 index;
+  u32 address;
+
+  if (regs->eax != E820_FUNCTION || regs->edx != E820_SIGNATURE
+      || regs->ecx < E820_ENTRY_SIZE)
+    {
+      int15_fail (regs);
+      return;
+    }
+
+  index = regs->ebx;
+
+  if (index >= E820_ENTRY_COUNT)
+    {
+      int15_fail (regs);
+      return;
+    }
+
+  address = ((u32)regs->es << 4) + (u16)regs->edi;
+  output = (struct e820_entry *)address;
+
+  *output = e820_map[index];
+
+  regs->eax = E820_SIGNATURE;
+  regs->ecx = E820_ENTRY_SIZE;
+
+  index++;
+  regs->ebx = index < E820_ENTRY_COUNT ? index : 0u;
+  regs->flags &= (u16)~BIOS_CF;
+}