Re: Correct IDSEL generation/identification.. ??

["Kevin Brace" <kevinbraceusenet@hotmail.com>]

Abraham,

See the comments below.


>From: Abraham Thomas <abraham_ktm@yahoo.com>
>To: pci-sig@znyx.com
>Subject: Correct IDSEL generation/identification.. ??
>Date: Mon, 23 Dec 2002 05:55:16 -0800 (PST)
>
>Hello experts,
>
>i have a doubt relating to IDSEL implementation...
>if i understand right this is what the spec means:
>
>the host-pci bridge decodes the "device number" in the
>32 bit address (config. access to address port) it
>gets from the CPU and uses one of the AD11-AD31 lines
>(or more practically AD16-AD31 AD lines) for
>generating IDSEL during address phase of conf/
>transaction instead of using a separate IDSEL signal.
>this IDSEL acts as a chip select for any one of
>various devices in the bus. in modern PCs, the IDSEL
>of the 1st device on the bus (which i believe means
>the 1st slot?? -- clarify if incorrect) is connected
>(/resistively coupled???) to AD16, 2nd to AD17 and so
>on...
>
>my doubt is: if we need to tell our target device to
>use a particular AD line as chip select for it, how do
>we know which AD line to tell it bcos this may change
>if we change the slot in which we put our pci card?
>won't our device work if placed on any other slot (ie,
>if it takes any other device number??) bcos the the
>logic for decoding the IDSEL is "burn"t inside the
>target device... say, we could tell our card to OK a
>config access if AD16 line is asserted. what if this
>card is put in the next slot? in this case it won't
>work.. it will work only if AD17 is asserted since
>this is the way that the H/PCI bridge generates IDSEL.
>
>what is the way around this? what's wrong in my
>understanding? if there is no fixed logic to
>understand which AD line is meant for our device, how
>does the right IDSEL reach the right device?
>
>kindly clarify..
>
>thanks in advance
>Happy Holidays!!
>
>regards,
>Abraham Thomas
>


        When your device is decoding AD[31:0] during a Type 0 configuration 
transaction (Only PCI-to-PCI bridges respond to a Type 1 configuration 
transaction.), you are not supposed to look at AD[31:11].
In a typical implementation, IDSEL is connected to one the lines of 
AD[31:16], but that's just one example of implementing IDSEL, and supposedly 
other implementations that don't use AD[31:16] are possible according to PCI 
2.2 specification page 37.


Kevin Brace (If someone wants to respond to what I wrote, I prefer if you 
will do so within the mailing list.)

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