Re: Split Completion Issue

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

Hi Srikiran,

>My Question :
>
>     When I transfer the 8 bytes with Split Completion cycle, can I set
>the BCM bit and change the bytecount to 8 bytes even though it is
>not to disconnect the transaction on the first ADB ??
>The PCI-X specification Ver1.0 has not specified the completer for a
>Split Completion cycle setting the BCM bit for bytecount overflow case.
>It specifies for disconnection on the first ADB only.
>  

No, You cannot set the byte count to 8 and try to disconnect at a non ADB aligned address.

But with your particular case, you have two options.
1.  Generate a Device specific error or byte count out of range completion, so that the initiator knows that his attempt is no good.
2.  Return first 8 dwords as they are, and return the others till ADB as all zero's or FF's and disconnect at ADB. (This means that you have a ADB of memory with first 8 dwords as active and all other implementated as dead or zero's).

Also can you tell me that why is that in a PCI-X envoirnment, you are requesting 4K of space for 8 DWORDS. You can ask only one ADB of space
as that is the min. requirement for PCI-X for BAR allocation.

Is it possible that the initiator accessing your device does not know that you are just a 8 Dword device ?? Not anybody and everybody will try to access your device.

Amit Shah
DCM Technologies
Austin Design Center


---------- Original Message ----------------------------------
From: Srikiran Dravida <SrikiranD@ami.com>
Date: Mon, 12 Jun 2000 12:13:09 -0400

>Hi  All,
>
>       I have a BAR which requests for 4k address space. But the device
>connected to this BAR can handle only 8bytes read or 8 bytes write.
>   In the case of write I do a Single Dataphase Disconnect and forward the
>cycle to the device.
>   In the case of a read I signal a Split Response, but I have no way of
>informing
>the initiator that I can handle only 8bytes of data and no more.
> So if an initiator issues a read request with more than 8 bytes, say it
>asked for 16bytes at a 64-bit aligned address, I respond with Split
>Response. In the
>Split Completion cycle I transfer 8 bytes (fetched from the device) only. I
>do this
>by setting BCM bit and changing the bytecount field to 8 bytes in the
>attribute phase of the Split Completion cycle. For the remaining bytecount
>I do a Split Completion Message cycle with the overflow information.
>
>My Question :
>
>     When I transfer the 8 bytes with Split Completion cycle, can I set
>the BCM bit and change the bytecount to 8 bytes even though it is
>not to disconnect the transaction on the first ADB ??
>The PCI-X specification Ver1.0 has not specified the completer for a
>Split Completion cycle setting the BCM bit for bytecount overflow case.
>It specifies for disconnection on the first ADB only.
>  
>  Thanks
>
>- SriKiran Dravida.
>
>