SMBios是一份軟體的spec, 他定義了兩個table, 即EPS ( Entry Point structure) 和 Structure Table
EPS位於記憶體1MB以下64K之間，也就是0xF0000 ~ 0xFFFFF之間。透過程式搜尋搜尋_SM_和_DMI_這兩個Keyword可以找到這個table。
以下是 SMBIOS 2.1 (32-bit) Entry Point structure，這邊列出比較重要的部分
Offset
|
Name
|
Length
|
Description
|
00h
|
Anchor String
|
4 BYTEs
|
_SM_, specified as
four ASCII characters (5F 53 4D 5F).
|
10h
|
Intermediate Anchor
String
|
5 BYTEs
|
_DMI_, specified as
five ASCII characters (5F 44 4D 49 5F)
|
16h
|
Structure Table
Length
|
WORD
|
Total length of
SMBIOS Structure Table, pointed to by the Structure Table Address, in bytes
|
18h
|
Structure Table
Address
|
DWORD
|
32-bit physical
starting address of the read-only SMBIOS Structure
|
1Ch
|
Number of SMBIOS
Structures
|
WORD
|
Handle的數量
|
透過18H這個offset可以找到一塊記憶體:Structure Table，這裡面有一堆handle, 每個handle都代表一個type(有些type不只一個handle)。任何 type 的 Structure都有定義以下這幾個共通的欄位
Offset
|
Name
|
Length
|
Description
|
00h
|
Type
|
Byte
|
which type
|
01h
|
Length
|
Byte
|
Specifies the length
of the formatted area of the structure, starting at the Type field. The
length of the structure’s string-set is not included.
|
02h
|
Handle
|
WORD
|
這是第幾個handle
|
下兩圖是Structure的兩種格式，一種是含有string, 一種是沒有(注意他的Length不含string), 如果是含有string的，最後須再加個 '0' 代表結束
最後列出有哪些Type，細部的Type欄位定義請參考spec
Type
|
Description
|
|---|---|
0
|
BIOS Information
|
1
|
System Information
|
2
|
Baseboard (or Module) Information
|
3
|
System Enclosure or Chassis
|
4
|
Processor Information
|
5
|
Memory Controller Information (Obsolete)
|
6
|
Memory Module Information (Obsolete)
|
7
|
Cache Information
|
8
|
Port Connector Information
|
9
|
System Slots
|
10
|
On Board Devices Information
|
11
|
OEM Strings
|
12
|
System Configuration Options
|
13
|
BIOS Language Information
|
14
|
Group Associations
|
15
|
System Event Log
|
16
|
Physical Memory Array
|
17
|
Memory Device
|
18
|
32-Bit Memory Error Information
|
19
|
Memory Array Mapped Address
|
20
|
Memory Device Mapped Address
|
21
|
Built-in Pointing Device
|
22
|
Portable Battery
|
23
|
System Reset
|
24
|
Hardware Security
|
25
|
System Power Controls
|
26
|
Voltage Probe
|
27
|
Cooling Device
|
28
|
Temperature Probe
|
29
|
Electrical Current Probe
|
30
|
Out-of-Band Remote Access
|
31
|
Boot Integrity Services (BIS) Entry Point
|
32
|
System Boot Information
|
33
|
64-Bit Memory Error Information
|
34
|
Management Device
|
35
|
Management Device Component
|
36
|
Management Device Threshold Data
|
37
|
Memory Channel
|
38
|
IPMI Device Information
|
39
|
System Power Supply
|
40
|
Additional Information
|
41
|
Onboard Devices Extended Information
|
42
|
Management Controller Host Interface
|
126
|
Inactive
|
127
|
End-of-Table
|
128–255
|
Available for system- and OEM- specific information
|
特別介紹Type 9 (System Slot) 看到一個有趣的現象, 基本上主機板有幾個PCIe插槽就要有幾個handle是Type 9的，但是一般PCIe的lane除了一條x16的以外大部分都是共享的，如某家主機板的規格:
>> 1*PCI-E 3.0 x16 + 1*PCI-E 3.0 x8 + 2*PCI-E x4
>> PCI-E x4 插槽與PCI-E x8 插槽共享頻寬。
但SMBios對Type 9定義了Bus/Dev/Func的號碼的欄位, 這樣不是很怪? 我提供我的看法:
若所有slot都沒有插裝置，除了x16會有固定的Bus號碼以外，因為系統未決定怎麼分配共享的lane(且通常沒插裝置時這些對外延伸bus的P2P bridge會被關閉), 所以共享lane的slot其Bus號碼應該應為0xFF, 也就是unknown。
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