115 lines
2.5 KiB
C
115 lines
2.5 KiB
C
// mm.c
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// 09/01/03 Josh Holtrop
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//The total amount of physical memory available (bytes)
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#define BITMAP_SIZE 0x20000
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dword mm_totalmem = 0;
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dword mm_megabytes;
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byte page_bitmap[BITMAP_SIZE]; //used to store a bit for each page that is used, 0 if available
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//0x20000*(8 bits/byte)=0x100000 pages in 4gb total
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//This function initializes the memory manager's linked list, filling it with the
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// memory areas returned by bios interrupt 0x8E20
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void mm_init()
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{
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dword memmap_entries = *(dword *)0xC009040A;
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memmap_entry *maps = (memmap_entry *) 0xC0092000;
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dword a;
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for (a = 0; a < BITMAP_SIZE; a++)
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{
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page_bitmap[a] = 0xFF; //all pages used
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}
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for (a = 0; a < memmap_entries; a++)
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{
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if (maps[a].attributes == 1) // (1) mem free to OS
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{
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mm_totalmem += maps[a].limit.lowdword;
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if ((maps[a].base.lowdword + maps[a].limit.lowdword) >= (FREERAM_START+4096)) //goes past where we start freeram
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{
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if (maps[a].base.lowdword < FREERAM_START)
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{
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mm_pfreen(FREERAM_START, (maps[a].limit.lowdword - (FREERAM_START - maps[a].base.lowdword)) >> 12);
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}
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else
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{
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mm_pfreen(maps[a].base.lowdword, maps[a].limit.lowdword >> 12); //set the appropriate bits as "free" in the page bitmap
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}
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}
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}
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}
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if (mm_totalmem % 0x100000)
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mm_megabytes = (mm_totalmem >> 20) + 1;
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else
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mm_megabytes = mm_totalmem >> 20;
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}
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void mm_pfreen(dword base, dword pages)
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{
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dword a;
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dword max = base + (pages << 12);
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for (a = base; a < max; a += 4096)
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{
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mm_pfree(a);
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}
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}
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void mm_pfree(dword base)
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{
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// dword pageNumber = base >> 12; // >>12 == /4096
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dword byteNumber = base >> 15; //pageNumber >> 3; //pageNumber/8
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dword bitNumber = (base >> 12) % 8; //pageNumber % 8;
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page_bitmap[byteNumber] = page_bitmap[byteNumber] & ((0x01 << bitNumber) ^ 0xFF);
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}
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void *mm_palloc()
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{
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dword bite;
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for (bite = 0; bite < BITMAP_SIZE; bite++)
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{
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if (page_bitmap[bite] != 0xFF) //there is an available page within this 8-page region
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{
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int bit;
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for (bit = 0; bit < 8; bit++)
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{
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if (!(page_bitmap[bite] & (1 << bit))) //this bite/bit combination is available
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{
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return (void *)((bite << 15) + (bit << 12));
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}
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}
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}
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bite++;
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}
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return 0; //no free page
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}
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dword mm_freemem()
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{
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dword a;
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dword pages = 0;
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for (a = 0; a < BITMAP_SIZE; a++)
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{
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int bit;
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for (bit = 0; bit < 8; bit++)
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{
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if (!(page_bitmap[a] & (1 << bit)))
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pages++;
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}
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}
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return pages << 12;
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}
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