Re: pci-x query

["Amit Shah" <Amit@dcmtech.com>]

>    2] This is regarding the split response during DWORD transactions. 
>
>        I am not getting the significance of the Split Response for DWORD transaction. If it is a DWORD transaction, why it is necessary to give split response instead of 
>        completing the transaction?  

Consider a case wherein the master who originally started a transaction starts a transaction towards a target, which resides behind a PCI-X to PCI-X brodge. Now the bridge has to initially decode the cycle, and give a split to the master. Then the bridge will act as a master on the Secondary side and initiate the cycle, where the original target will decode it and return the data (via a split completion or Single data transfer). In turn, the bridge will accept the completion data and will issue a split completion back on the original master on primary.

In PCI, this scenario was taken care of by the bridge by making the incoming cycle as a delayed cycle. In this scenario, the original master has to try the same cycle till it gets a response other than a retry from Bridge.

Now in PCI-X, the bridge will issue a split, so the master does not have to re-arbitrate for the PCI-X bus. Now it is bridge's responsibility to return the requested data. So let the down stream cycle be a dword or a burst, bridge has to issue a split.

I hope i answered your question.

Amit Shah
Design Engr
DCM Technologies


---------- Original Message ----------------------------------
From: "Madhura Bokil" <madhura@controlnet.co.in>
Date: Tue, 29 Aug 2000 19:06:03 +0530

>Hello,
>  I have some queries regarding PCI-X. 
>
>    1] This is regarding the PCI-X status register. [Pg. 141 from PCI-X Addendum Rev. 1.0]
>
>        Bits 15-8 [Bus Number] & 7-3 [Device Number] are mentioned as Read-only bits in the standard. At the same time it is mentioned that these bits should be updated 
>        during each Configuration Write Transaction. If these bits are to be updated during every Configuration Write transaction, how these bits can be read-only? 
>
>    2] This is regarding the split response during DWORD transactions. 
>
>        I am not getting the significance of the Split Response for DWORD transaction. If it is a DWORD transaction, why it is necessary to give split response instead of 
>        completing the transaction?  
>
>I will be thankful if somebody can help me to clear these queries.
>
>Regards,
>  
>Madhura Bokil.
>
>
>
>