// mm.c
// Author: Josh Holtrop
// Created: 09/01/03
// Modified: 03/08/04

#include "hos_defines.h"
#include "mm.h"

//The total amount of physical memory available (bytes, 1 bit per page)
#define BITMAP_SIZE	0x20000
dword	mm_totalmem = 0;
dword	mm_megabytes = 0;
byte	page_bitmap[BITMAP_SIZE];	//used to store a bit for each page that is used, 0 if available
					//0x20000*(8 bits/byte)=0x100000 pages in 4gb total

//This function initializes the memory manager's linked list, filling it with the
// memory areas returned by bios interrupt 0x8E20
void	mm_init()
{
	dword	memmap_entries = *(dword *)BOOT_MEMMAP_ENTRIES;
	memmap_entry	*maps = (memmap_entry *) BOOT_FIRST_MEMMAP;
	dword a;
 	for (a = 0; a < BITMAP_SIZE; a++)
 	{
 		page_bitmap[a] = 0xFF;	//all pages used
 	}
	for (a = 0; a < memmap_entries; a++)
	{
		if (maps[a].attributes == 1)		// (1) mem free to OS
		{
			mm_totalmem += maps[a].limit.lowdword;
			if  ((maps[a].base.lowdword + maps[a].limit.lowdword) >= (FREERAM_START+4096))	//goes past where we start freeram
			{
				if (maps[a].base.lowdword < FREERAM_START)
				{
					mm_pfreen(FREERAM_START, (maps[a].limit.lowdword - (FREERAM_START - maps[a].base.lowdword)) >> 12);
				}
				else
				{
					mm_pfreen(maps[a].base.lowdword, maps[a].limit.lowdword >> 12);	//set the appropriate bits as "free" in the page bitmap
				}
			}
		}
	}
	if (mm_totalmem % 0x100000)
		mm_megabytes = (mm_totalmem >> 20) + 1;
	else
		mm_megabytes = mm_totalmem >> 20;
}


// This function frees a certain number of pages starting at the address
//  specified in base for a length of pages pages
void	mm_pfreen(dword base, dword pages)
{
	dword a;
	dword max = base + (pages << 12);
	for (a = base; a < max; a += 4096)
	{
		mm_pfree(a);
	}
}


// This function frees a single page
void	mm_pfree(dword base)
{
//	dword pageNumber = base >> 12;	// >>12 == /4096
	dword byteNumber = base >> 15;	//pageNumber >> 3;	//pageNumber/8
	dword bitNumber = (base >> 12) % 8; //pageNumber % 8;
	page_bitmap[byteNumber] = page_bitmap[byteNumber] & ((0x01 << bitNumber) ^ 0xFF);
}


// This function allocates a single page, returning its physical address
void	*mm_palloc()
{
	dword bite;
	for (bite = 0; bite < BITMAP_SIZE; bite++)
	{
		if (page_bitmap[bite] != 0xFF)	//there is an available page within this 8-page region
		{
			int bit;
			for (bit = 0; bit < 8; bit++)
			{
				if (!(page_bitmap[bite] & (1 << bit)))	//this bite/bit combination is available
				{
					page_bitmap[bite] = page_bitmap[bite] | (1 << bit);	//set page as used
					return (void *)((bite << 15) | (bit << 12));
				}
			}
		}
	}
	return 0;	//no free page
}


// This function reports the number of bytes of free physical memory
dword	mm_freemem()
{
	dword a;
	dword pages = 0;
	for (a = 0; a < BITMAP_SIZE; a++)
	{
		int bit;
		for (bit = 0; bit < 8; bit++)
		{
			if (!(page_bitmap[a] & (1 << bit)))
				pages++;
		}
	}
	return pages << 12;
}


dword	mm_getTotalMem()
{
	return mm_totalmem;
}


dword	mm_getTotalMegs()
{
	return mm_megabytes;
}