[mubios] Implement INT 15h E820h

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

5 files changed, 92 insertions, 0 deletions

diff --git a/mubios/arch/interrupt.S b/mubios/arch/interrupt.S
index b3a461b..805cc50 100644
--- a/mubios/arch/interrupt.S
+++ b/mubios/arch/interrupt.S
@@ -87,3 +87,4 @@ int1a_return:
 
 	BIOS_SERVICE_ENTRY int10_entry, 0x10
 	BIOS_SERVICE_ENTRY int13_entry, 0x13
+	BIOS_SERVICE_ENTRY int15_entry, 0x15
diff --git a/mubios/core/bda.c b/mubios/core/bda.c
index d7be60c..8417605 100644
--- a/mubios/core/bda.c
+++ b/mubios/core/bda.c
@@ -59,6 +59,7 @@ extern void irq1_entry (void);
 extern void int1a_entry (void);
 extern void int10_entry (void);
 extern void int13_entry (void);
+extern void int15_entry (void);
 
 static void
 install_ivt_entry (u8 vector, void (*handler) (void))
@@ -83,4 +84,5 @@ ivt_init (void)
   install_ivt_entry (0x1Au, int1a_entry);
   install_ivt_entry (0x10u, int10_entry);
   install_ivt_entry (0x13u, int13_entry);
+  install_ivt_entry (0x15u, int15_entry);
 }
diff --git a/mubios/core/interrupt.c b/mubios/core/interrupt.c
index a9b3ce6..9c71492 100644
--- a/mubios/core/interrupt.c
+++ b/mubios/core/interrupt.c
@@ -35,6 +35,10 @@ bios_service_dispatch (u8 vector, struct bios_regs *regs)
       int13_service (regs);
       break;
 
+    case 0x15u:
+      int15_service (regs);
+      break;
+
     default:
       regs->eax = 0x0100u;
       regs->flags |= 0x0001u;
diff --git a/mubios/include/bios.h b/mubios/include/bios.h
index 9c14a42..1094bed 100644
--- a/mubios/include/bios.h
+++ b/mubios/include/bios.h
@@ -57,5 +57,6 @@ struct bios_regs;
 void bios_service_dispatch (u8 vector, struct bios_regs *regs);
 void int10_service (struct bios_regs *regs);
 void int13_service (struct bios_regs *regs);
+void int15_service (struct bios_regs *regs);
 
 #endif // MUBIOS_BIOS_H
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;
+}