PCI power management

["Gelder, Dimitri van" <DGelder@tulip.nl>]

     Dear PCI reflector,
     
     Power management is a hot issue these days even in "normal computers" 
     that get their supply from mains. The PCI bus power management 
     interface specification revision 0.93 gives a lot of useful 
     information. Looking at the hardware side some additions can be made. 
     For signalling the sleep state of the computer no hardware
     is needed but for signalling its awakening a PCI_PM line can help 
     hardware to recover from a real power saving state. Assuming the name 
     for a PCI wake up line is PCI_PM the function of this line is could 
     be.
     
     PCI_PM
      
     When PCI_PM is high the system is working in normal state. In an 
     environment where PCI_PM is not controlled it can be pulled up using 
     the motherboard supply. In power saving PCI_PM goes low. This can be 
     the falling edge to put a device to sleep but this is not necessary 
     the case. A sleep state can also be timed from this edge or can be 
     software controlled. The rising edge triggers the device to wake up a 
     gain. This edge is more important since there is no other way 
     signalling the system awakening while not keeping the device almost 
     fully active.
     
     Adding this pin to the PCI interface should make power saving more a 
     rule than an option. PIN 10 on the B side of the PCI Connector would 
     give a good place to the signal PCI_PM.
      
     Yours Sincerely,
     
     Dimitri van Gelder
      
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