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/*
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, 0x00000000u, 0x00000000u, 1u } };
#define E820_ENTRY_COUNT ((u32)(sizeof (e820_map) / sizeof (e820_map[0])))
#define E820_MEMORY_BASE 0x00100000u
#define E820_FALLBACK_END 0x08000000u
#define CMOS_EXTENDED_MEMORY_LOW_16M 0x30u
#define CMOS_EXTENDED_MEMORY_HIGH_16M 0x31u
#define CMOS_EXTENDED_MEMORY_LOW 0x34u
#define CMOS_EXTENDED_MEMORY_HIGH 0x35u
static u32
get_memory_end (void)
{
u16 units;
u16 extended_kib;
u32 memory_end;
units = (u16)cmos_read8 (CMOS_EXTENDED_MEMORY_LOW)
| (u16)((u16)cmos_read8 (CMOS_EXTENDED_MEMORY_HIGH) << 8);
if (units != 0u)
{
memory_end = 0x01000000u + ((u32)units << 16);
}
else
{
extended_kib
= (u16)cmos_read8 (CMOS_EXTENDED_MEMORY_LOW_16M)
| (u16)((u16)cmos_read8 (CMOS_EXTENDED_MEMORY_HIGH_16M) << 8);
if (extended_kib != 0u)
memory_end = E820_MEMORY_BASE + ((u32)extended_kib << 10);
else
memory_end = E820_FALLBACK_END;
}
return memory_end;
}
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 entry;
struct e820_entry *output;
u32 index;
u32 address;
u32 memory_end;
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;
entry = e820_map[index];
if (index == 3u)
{
memory_end = get_memory_end ();
entry.length_low = memory_end - E820_MEMORY_BASE;
}
*output = entry;
regs->eax = E820_SIGNATURE;
regs->ecx = E820_ENTRY_SIZE;
index++;
regs->ebx = index < E820_ENTRY_COUNT ? index : 0u;
regs->flags &= (u16)~BIOS_CF;
}
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