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re: Power Management spec. question




>  From: raw@brahms.amd.com (Robert Williams), on 3/4/97 6:29 PM:
>  
>  The PCI Bus Power Management Interface Spec., Rev. 0.99a states that the 
>  DSI (Device Specific Initailization) bit in the PMC register is meant 
>  for fucntions which require specific programming in order to appear 
>  as compataible device types.  Should this bit be set for any device
>  that needs some software initailization after it leaves state D3?
>  
>  For example a network device may need to have its multicast address
>  filter reloaded after power is restored.  Should this function have
>  its DSI bit set?
>  
>      bob.williams@amd.com
>  
The Device Specific Initialization (DSI) bit is really intended for devices
that would normally be able to use a generic device driver (devices such as
standard modems, or compatible sound cards), but require unique initialization
to put them into such a compatibility mode.

One example might be a DSP based audio controller that gets configured by it's
option ROM to be put into a sound blaster compatible configuration.  When the
OS loads, an SB compatible driver could be loaded to control the device and
everything would work fine, until the device was placed into the D3 state.
Since all configuration information may be lost in the D3 state, when the DSP
card was restored to D0 uninitialized, it would have "lost" the compatibility
configuration, thus the compatible driver would be unable to communicate with
it.

The DSI bit informs the OS that it needs to use a device specific driver, and
not a compatible driver, if it plans on putting the device into D3.

In the case of a network device, the DSI should only be set if the device
supports some sort of compatible device driver which may not understand how to
fully re-initialized the device.  If the network device is itself a unique
device, and doesn't support any compatible modes, then its device specific
driver should always be loaded, and the DSI bit is unnecessary.
 
Regards,
Brian Belmont		Voice: 	972.997.6021
Texas Instruments	Fax:	972.997.6301
PC Systems Lab		MsgID:	BVB1
					Internet: bbelmont@ti.com