hos/kernel/mm/mm.c

// mm.c
// Author: Josh Holtrop
// Created: 09/01/03
// Modified: 07/12/04

#include "kernel.h"
#include "mm/mm.h"
#include "multiboot.h"
#include "hos_defines.h"

extern	mb_info_t mb_info_block;
extern	mb_mmap_t mb_mmap[MAX_MMAP];
extern	u32_t mmap_entries;
extern	mb_module_t mb_modules[MAX_MODULES];

u32_t	mm_totalmem;
u32_t	mm_megabytes;
u32_t	mm_freepages;
u32_t	mm_first_free_byte;
byte	page_bitmap[MM_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()
{
	u32_t a;
 	for (a = 0; a < MM_BITMAP_SIZE; a++)		//mark all pages used
 	{
 		page_bitmap[a] = 0xFF;
 	}
	for (a = 0; a < mmap_entries; a++)		//free BIOS #1 areas
	{
		if (mb_mmap[a].type == 1)		// (1) mem free to OS
		{
			mm_totalmem += mb_mmap[a].length;
			u32_t freethis = mb_mmap[a].base;
			u32_t limit = mb_mmap[a].base + mb_mmap[a].length - 4096;
			while (freethis <= limit)
			{
				if (freethis >= PHYS_LOAD)	//above physical kernel load point
					mm_pfree(freethis);
				freethis += 4096;
			}
		}
	}
	mm_preserven(PHYS_LOAD, ((u32_t)&_end - (u32_t)&start) >> 12);	//reserve kernel memory
	int i;
	for (i = 0; i < mb_info_block.mods_count; i++)	//reserve module memory
	{
		mm_preserven(mb_modules[i].mod_start - VIRT_OFFSET, (mb_modules[i].mod_end - mb_modules[i].mod_start) >> 12);
	}
	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(u32_t base, u32_t pages)
{
	pages = base + (pages << 12);		//convert #pages to #bytes
	for (; base < pages; base += 4096)
		mm_pfree(base);
}


// This function frees a single page
void	mm_pfree(u32_t base)
{
//	u32_t pageNumber = base >> 12;	// >>12 == /4096
	u32_t byteNumber = base >> 15;	//pageNumber >> 3;	//pageNumber/8
	u32_t bitNumber = (base >> 12) & 0x07; //pageNumber % 8;
	page_bitmap[byteNumber] = page_bitmap[byteNumber] & ((0x01 << bitNumber) ^ 0xFF);
	mm_freepages++;
	if (byteNumber < mm_first_free_byte)
		mm_first_free_byte = byteNumber;
}


// This function reserves a certain number of pages starting at the address
//  specified in base for a length of pages pages
void	mm_preserven(u32_t base, u32_t pages)
{
	pages = base + (pages << 12);		//convert #pages to #bytes
	for (; base < pages; base += 4096)
		mm_preserve(base);
}


// This function reserves a single page
void	mm_preserve(u32_t base)
{
//	u32_t pageNumber = base >> 12;	// >>12 == /4096
	u32_t byteNumber = base >> 15;	//pageNumber >> 3;	//pageNumber/8
	u32_t bitNumber = (base >> 12) & 0x07; //pageNumber % 8;
	page_bitmap[byteNumber] = page_bitmap[byteNumber] | (0x01 << bitNumber);
	mm_freepages--;
}


// This function allocates a single page, returning its physical address
u32_t	mm_palloc()
{
	u32_t bite;
	for (bite = mm_first_free_byte; bite < MM_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
				{
					mm_first_free_byte = bite;	//start searching from here next time
					mm_freepages--;
					page_bitmap[bite] = page_bitmap[bite] | (1 << bit);	//set page as used
					return ((bite << 15) | (bit << 12));
				}
			}
		}
	}
	return 0;	//no free page
}


// This function reports the number of bytes of free physical memory
u32_t	mm_getFreeMem()
{
	return mm_freepages << 12;
}


u32_t	mm_getFreePages()
{
	return mm_freepages;
}


u32_t	mm_getTotalMem()
{
	return mm_totalmem;
}


u32_t	mm_getTotalMegs()
{
	return mm_megabytes;
}