Code for managing memory. More...

Files
file	mm.c
	Implementation of basic memory functions.

file	mm.h
	Definition of basic memory sizes and functions.

Macros
#define	PAGE_SHIFT 12

#define	TABLE_SHIFT 9

#define	SECTION_SHIFT (PAGE_SHIFT + TABLE_SHIFT)

#define	PAGE_SIZE (1 << PAGE_SHIFT)

#define	SECTION_SIZE (1 << SECTION_SHIFT)

#define	LOW_MEMORY (2 * SECTION_SIZE)

#define	HIGH_MEMORY MMIO_BASE

#define	PAGING_MEMORY (HIGH_MEMORY - LOW_MEMORY)

#define	PAGING_PAGES (PAGING_MEMORY / PAGE_SIZE)

Functions
uint64_t	get_free_page ()

void	free_page (uint64_t p)

Detailed Description

Code for managing memory.

Macro Definition Documentation

◆ HIGH_MEMORY

#define HIGH_MEMORY MMIO_BASE

Start of Memory Mapped Registers.

See also: MMIO_BASE

◆ LOW_MEMORY

#define LOW_MEMORY (2 * SECTION_SIZE)

4MB (First 4 MB of memory reserved for the kernel image and init task stack).

2*2MB = 4MB

◆ PAGE_SHIFT

#define PAGE_SHIFT 12

Bits to shift to define Page size.

◆ PAGE_SIZE

#define PAGE_SIZE (1 << PAGE_SHIFT)

PAGE_SIZE: 4KB

For kernel at address 0x0: Start of stack, 4MB available for kernel (except stack).
For kernel at address 0x8000: 4064KB available for kernel till 4MB.
For kernel at address 0x80000: 3584KB available for kernel till 4MB.
2^12 = 4096 = 4KB

◆ PAGING_MEMORY

#define PAGING_MEMORY (HIGH_MEMORY - LOW_MEMORY)

Available memory for paging

MMIO_BASE - 4MB

◆ PAGING_PAGES

#define PAGING_PAGES (PAGING_MEMORY / PAGE_SIZE)

Available 4KB pages

(MMIO_BASE - 4MB) / 4KB

◆ SECTION_SHIFT

#define SECTION_SHIFT (PAGE_SHIFT + TABLE_SHIFT)

Bits to shift to define Section size (= 21).

◆ SECTION_SIZE

#define SECTION_SIZE (1 << SECTION_SHIFT)

2^21 = 2048KB = 2MB

◆ TABLE_SHIFT

#define TABLE_SHIFT 9

Bits to shift to define Table size.

Function Documentation

◆ free_page()

void free_page ( uint64_t p )

Function for deallocating memory pages.

Parameters

p	64-bit address of page to be deallocated.

◆ get_free_page()

uint64_t get_free_page ( )

Function for allocating memory pages.

Returns

On success: Starting address (64-bit) of the allocated page.
On failure: 0

Files

Macros

Functions