怎樣讀寫SMBus上的Device—以擷取Intel平台上Memory的SPD資訊為例

How to access devices on SMBus--- Take reading SPD information (Intel platform) as example

 firing -2005/04/13

0. Essential skills before you start:

l         How to read/write PCI configuration space?

l         How to read/write I/O space under WindowsNT/2000… platform?

And an Intel south bridge datasheet as reference

1．  Basic steps

a.       Enable SMBus controller

b.       Get SMBus base address

c.       Read SPD information, according the device IDs

2．  Enable SMBus controller

LPC Interface Bridge Registers (D31:F0),  Offset: 40h (FUNC_DIS)，Bit0 :

Software sets this bit to disable the SMBus Host controller function.

0 = SMBus controller is enabled

1 = SMBus controller is disabled

This bit is set to 1(SMBus controller is disabled) by default. So, just set this bit to 0.

(How to make sure you have enabled SMBus controller? Go to ‘Device Manager’ and refresh it, and then check ‘System Device’, where you should find a PCI device named “Intel® 82801DB SMBus Controller” like.)

3．  Get SMBus base address

SMBus Controller PCI Register (D31:F3), offset: 20~23H. That’s the SMBus base address. Just read this base address. Normally, the address could be 0x500 or 0x5000

4．  Read SPD information

The SMBus DeviceID of memory bank0 is a0, bank1= 0xa2, and bank2 =0xa4

a. start

b. wait smbus ready

c. output Base+04, (DeviceID+1)

d. out Base+03, offset

e. out Base+02, 48H

f. wait 200ms

g. wait smbus ready

h. input base+05

i. OK

Note:

How to wait SMBus ready? Input Base+0, bit0==0 indicates smbus is ready, otherwise(bit0==1), smbus is busy