실제 코드로 구현 하면 아래와 같다. 더 자세히 ...

Memory Range Descriptors에 대한 협력 다이어그램:

열거형 타입
enum	MRD { MRD_UNKNOWN, MRD_MEMORY, MRD_RESERVED, MRD_ACPI, MRD_NVS }
	Type of Memory Range Descriptor. 더 자세히 ...

함수
void	mrd_init (void *addr)
	MRD 관리자를 초기화한다. 더 자세히 ...

struct mrd *	mrd_base (void)
	MRD 가 저장된 Base 주소를 반환한다. 더 자세히 ...

int	mrd_count (void)
	Descriptor 의 총 개수를 반환한다. 더 자세히 ...

int	mrd_get_type (int idx)
	지정된 인덱스에 해당하는 Descriptor 의 종류를 반환한다. 더 자세히 ...

void *	mrd_get_base (int idx)
	지정된 인덱스에 해당하는 Descriptor 의 시작 주소를 반환한다. 더 자세히 ...

unsigned long	mrd_get_size (int idx)
	지정된 Index에 해당하는 Descriptor 가 가리키는 영역의 크기를 반환 더 자세히 ...

상세한 설명

실제 코드로 구현 하면 아래와 같다.

작성자: Sung-jae Park nices.nosp@m.j@ni.nosp@m.cesj..nosp@m.com

날짜: 2011-7-18

x86 에서 지원되는 Memory 영역에 대한 Descriptor 관련 코드를 구현한다. MRD(Memory Range Descriptor)는 Stage 2 Loader 에서 Protected mode 로 전환하기 직전에 BIOS 가 제공하는 Service 를 이용해서 확보했다. E820 Method 로 Bios Service Routine 0x15 번에서 제공되고 있다.

아래 Table 은 ACPI Spec 문서에서 scrap 해 온 것이다.

Input

Register	Contents	Description
EAX	Function Code	E820h
EBX	Continuation	Contains the continuation value to get the next range of physical memory. This is the value returned by a previous call to this routine. If this is the first call, EBX must contain ZERO.
ES:DI	Buffer Pointer	Pointer to an Address Range Descriptor structure that the BIOS fills in.
ECX	Buffer Size	The length in bytes of the structure passed to the BIOS. The BIOS fills in the number of bytes of the structure indicated in ECX register, maximum, or whatever amount of structure the BIOS implements. The minimum size that must be supported by both the BIOS and the caller is 20 bytes. Future implementations might extend this structure.
EDX	Signature	'SMAP' Used by the BIOS to verify caller is requesting the system map information to returned in ES:DI

Output

Register	Contents	Description
CF	Carry Flag	Non-Carry - Indicates No Error
EAX	Signature	'SMAP' Signature to verify correct BIOS revision
ES:DI	Buffer Pointer	Returned Address Range Descriptor pointer. Same value as on input
ECX	Buffer Size	Number of bytes returned by the BIOS in the address range descriptor. The minimum size structure returned by the BIOS is 20 bytes.
EBX	Continuation	Contains the continuation value to get the next address range descriptor. The actual significance of the continuation value is up to the discretion of the BIOS. The caller must pass the continuation value unchanged as input to the next iteration of the E820 call in order to get the next Address Range Descriptor. A return value of zero means that this is the last descriptor. Note: the BIOS can also indicate that the last descriptor has already been returned during previous iterations by returning the carry flag set. The caller will ignore any other information returned by the BIOS when the carry flag is set.

이 Service Routine 은 다음 데이터를 return 한다.

Offset in Bytes

Name

Description

0

BaseAddrLow

Low 32 Bits of Base Address

4

BaseAddrHigh

High 32 Bits of Base Address

8

LengthLow

Low 32 Bits of Length in Bytes

12

LengthHigh

High 32 Bits of Length in Bytes

16

Type

Address type of this range

Value	Mnemonic	Description
1	AddressRangeMemory	This range is available RAM usable by the operating system.
2	AddressRangeReserved	This range of addresses is in use or reserved by the system and is not to be included in the allocatable memory pool of the operating system's memory manager.
3	AddressRangeACPI	ACPI Reclaim Memory. This range is available RAM usable by the OS after it reads the ACPI tables.
4	AddressRangeNVS	ACPI NVS Memory. This range of addresses is in use or reserve by the system and must not be used by the operating system. This range is required to be saved and restored across an NVS sleep.
5	AddressRangeUnusable	This range of addresses contains memory in which errors have been detected. This range must not be used by OSPM.
6	AddressRangeDisabled	This range of addresses contains memory that is not enabled. This range must not be used by OSPM.
Other	Undefined	Undefined. Reserved for future use. OSPM must treat any range of this type as if the type returned was AddressRangeReserved.

주의

The BIOS can use the AddressRangeReserved address range type to block out various addresses as not suitable for use by a programmable device. Some of the reasons a BIOS would do this are:

The address range contains system ROM.
The address range contains RAM in use by the ROM.
The address range is in use by a memory-mapped system device.
The address range is, for whatever reason, unsuitable for a standard device to use as a device memory space.
The address range is within an NVRAM device where reads and writes to memory locations are no longer successful, that is, the device was worn out.

20

Extended Attributes

Bits	Mnemonic	Description
0	Reserved	Reserved. Must be set to 0
1	AddressRangeNonVolatile	If set, the Address Range Descriptor represents non-volatile memory. Memory reported as non-volatile may require characterization to determine its suitability for use as conventional RAM
2	AddressRangeSlowAccess	If set, accesses to the described range may incur considerable latencies
3	AddressRangeErrorLog	If set, the address range descriptor represents memory used for logging hardware errors.
4-31	Reserved	Reserved for future use

주의

The BIOS returns address ranges describing baseboard memory.
The BIOS does not return a range description for the memory mapping of PCI devices, ISA Option ROMs, and ISA Plug and Play cards because the OS has mechanisms available to detect them.
The BIOS returns chip set-defined address holes that are not being used by devices as reserved.
Address ranges defined for baseboard memory-mapped I/O devices, such as APICs, are returned as reserved.
All occurrences of the system BIOS are mapped as reserved, including the areas below 1 MB, at 16 MB (if present), and at end of the 4-GB address space.
Standard PC address ranges are not reported. For example, video memory at A0000 to BFFFF physical addresses are not described by this function. The range from E0000 to EFFFF is specific to the baseboard and is reported as it applies to that baseboard.
All of lower memory is reported as normal memory. The OS must handle standard RAM locations that are reserved for specific uses, such as the interrupt vector table (0:0) and the BIOS data area (40:0).

다만, 이 Service Routine 을 사용하기 위해서는 Real Mode (16 bits) 여야 하기 때문에, Protected Mode 로 전환하기 전에, MRD 들을 얻어 오고, 특정 메모리 영역에 저장한 다음에 Stage 2 로 이동하여 해당 정보를 사용하도록 한다.

; Get the memory from the ACPI (E820h) services
        mov dword [KERNEL_ARGUMENT], 0
        xor ebx, ebx            ; Continuation
        mov es, ebx             ; ES
        mov edi, KERNEL_ARGUMENT + 4 ; DI (ES:DI) location of storing data
        mov ecx, 20             ; Buffer size, 20 bytes
        mov edx, 0x534d4150     ; Signature
e820_get_desc:
        mov eax, 0x0000E820     ; function ID
        clc                     ; Clear carry flag
        int 0x15                ; Invoke interrupt 0x15
        jc e820_error           ; Check the carry flag
        cmp eax, 0x534d4150     ; Check the signature
        jne e820_error
        cmp ecx, 20             ; Check the minimum size of descriptor
        jl no_e820
        add edi, ecx            ; Move pointer to next
        cmp edi, E820_BOUND     ; Compare the boundary of memory for descriptors
        jge e820_overflow
        inc dword [KERNEL_ARGUMENT]
        cmp ebx, 0              ; Check the continuation value
        jne e820_get_desc

열거형 타입 문서화

enum MRD

Type of Memory Range Descriptor.

열거형 멤버
MRD_UNKNOWN	Unknown
MRD_MEMORY	AddressRangeMemory
MRD_RESERVED	AddressRangeReserved
MRD_ACPI	AddressRangeACPI
MRD_NVS	AddressRangeNVS

함수 문서화

struct mrd* mrd_base ( void )

MRD 가 저장된 Base 주소를 반환한다.

반환값: MRD 가 저장된 Base 주고

int mrd_count ( void )

Descriptor 의 총 개수를 반환한다.

반환값: Descriptor 의 전체 개수

이 함수를 호출하는 함수들에 대한 그래프입니다.:

void* mrd_get_base ( int idx)

지정된 인덱스에 해당하는 Descriptor 의 시작 주소를 반환한다.

매개변수

[in] idx 인덱스

반환값: Index 에 해당하는 Descriptor 의 시작주소

이 함수를 호출하는 함수들에 대한 그래프입니다.:

unsigned long mrd_get_size ( int idx)

지정된 Index에 해당하는 Descriptor 가 가리키는 영역의 크기를 반환

매개변수

[in] idx 인덱스

반환값: Index에 해당하는 Descriptor 가 가리키는 영역의 크기

이 함수를 호출하는 함수들에 대한 그래프입니다.:

int mrd_get_type ( int idx)

지정된 인덱스에 해당하는 Descriptor 의 종류를 반환한다.

매개변수

[in] idx 인덱스

반환값: Index 에 해당하는 Descriptor 의 종류

이 함수를 호출하는 함수들에 대한 그래프입니다.:

void mrd_init ( void * addr)

MRD 관리자를 초기화한다.

반환값: void 없음

이 함수를 호출하는 함수들에 대한 그래프입니다.: