80 lines
1.8 KiB
C
80 lines
1.8 KiB
C
#include <stddef.h>
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#include <mm/pmm.h>
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#define PAGE_SIZE 4096
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#define BITMAP_SIZE (1024 * 1024) /* Supports up to 4GB RAM (1 bit per page) */
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static uint8_t bitmap[BITMAP_SIZE / 8];
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static uint32_t total_pages;
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static uint32_t used_pages = 0;
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static inline void set_bit(uint32_t idx)
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{
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bitmap[idx / 8] |= (1 << (idx % 8));
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}
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static inline void clear_bit(uint32_t idx)
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{
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bitmap[idx / 8] &= ~(1 << (idx % 8));
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}
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static inline int test_bit(uint32_t idx)
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{
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return (bitmap[idx / 8] >> (idx % 8)) & 1;
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}
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void pmm_init(multiboot_info_t* mb_info)
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{
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total_pages = 0x100000; /* 4GB / 4KB = 1M pages */
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for (uint32_t i = 0; i < total_pages / 8; i++)
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{
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bitmap[i] = 0xFF; /* Mark all as used */
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}
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multiboot_memory_map_t* mmap = (multiboot_memory_map_t*) mb_info->mmap_addr;
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while ((uint32_t)mmap < mb_info->mmap_addr + mb_info->mmap_length)
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{
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if (mmap->type == 1) /* Usable */
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{
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uint64_t base = mmap->addr;
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uint64_t len = mmap->len;
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for (uint64_t addr = base; addr < base + len; addr += PAGE_SIZE)
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{
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if (addr >= 0x210000) /* Skip first 2.1MB, or ≈ 2.06MiB */
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{
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uint32_t idx = addr / PAGE_SIZE;
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if (idx >= total_pages)
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{
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continue; /* skip entries above 4GB */
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}
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clear_bit(idx);
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used_pages--;
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}
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}
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}
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mmap = (multiboot_memory_map_t*)((uint32_t)mmap + mmap->size + sizeof(mmap->size));
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}
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}
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void* alloc_page(void) {
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for (uint32_t i = 0; i < total_pages; i++)
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{
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if (!test_bit(i))
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{
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set_bit(i);
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used_pages++;
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return (void*)(i * PAGE_SIZE);
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}
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}
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return NULL; /* Out of memory */
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}
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void free_page(void* ptr)
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{
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uint32_t idx = (uint32_t)ptr / PAGE_SIZE;
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clear_bit(idx);
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}
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