88 lines
2.3 KiB
C
88 lines
2.3 KiB
C
#include "pmm.h"
|
|
#include "arch.h"
|
|
|
|
#define BITMAP_SIZE 32768 // Supports up to 1GB of RAM
|
|
#define USABLE_REGION_SIZE 32
|
|
|
|
static uint8_t page_bitmap[BITMAP_SIZE];
|
|
static uint64_t total_pages = 0;
|
|
static uint64_t free_pages = 0;
|
|
|
|
void pmm_init()
|
|
{
|
|
memory_map_t memory_map = arch_api.get_memory_map();
|
|
|
|
memset(page_bitmap, 0xFF, BITMAP_SIZE);
|
|
|
|
for (size_t i = 0; i < memory_map.num_regions; i++)
|
|
{
|
|
memory_region_t region = memory_map.regions[i];
|
|
|
|
uint64_t start_page = region.base_address / arch_api.page_size();
|
|
uint64_t num_pages = region.length / arch_api.page_size();
|
|
|
|
for (uint64_t page = start_page; page < start_page + num_pages; page++)
|
|
{
|
|
if (page < BITMAP_SIZE * 8)
|
|
{
|
|
page_bitmap[page / 8] &= ~(1 << (page % 8));
|
|
free_pages++;
|
|
total_pages++;
|
|
}
|
|
else
|
|
{
|
|
printf("System has more ram than the bitmap allows!\n");
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Reserve first 64MB which is reserved by boot code
|
|
for (uint64_t page = 0; page < (64 * 1024 * 1024) / arch_api.page_size(); page++)
|
|
{
|
|
if (page < BITMAP_SIZE * 8)
|
|
{
|
|
if (!(page_bitmap[page / 8] & (1 << (page % 8))))
|
|
{
|
|
page_bitmap[page / 8] |= (1 << (page % 8));
|
|
free_pages--;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Returns the address of first free physical page
|
|
uint64_t pmm_alloc_page()
|
|
{
|
|
for (size_t i = 0; i < BITMAP_SIZE; i++)
|
|
{
|
|
if (page_bitmap[i] != 0xFF)
|
|
{
|
|
for (int bit = 0; bit < 8; bit++)
|
|
{
|
|
if (!(page_bitmap[i] & (1 << bit)))
|
|
{
|
|
page_bitmap[i] |= (1 << bit);
|
|
free_pages--;
|
|
return ((i * 8 + bit) * arch_api.page_size());
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
// Frees the physical page at the specified address
|
|
void pmm_free_page(uint64_t addr)
|
|
{
|
|
uint64_t page = addr / arch_api.page_size();
|
|
if (page < BITMAP_SIZE * 8)
|
|
{
|
|
if (page_bitmap[page / 8] & (1 << (page % 8)))
|
|
{
|
|
page_bitmap[page / 8] &= ~(1 << (page % 8));
|
|
free_pages++;
|
|
}
|
|
}
|
|
} |