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Re: Merging of two 32-bits to form one 64-bit data

Hi there,

Interesting situation you have there.
I don't think there is any pci-recommendation or rule that will help you out

However, I think you can re-use a solution you already have in your bridge,
ie. during the
initiation of the 64-bit burst!

What do I mean with this?

During the *initiating* of a 64-bit transaction there are 2 requirements
that must be met:
a. the target  has 64-bit capabilities (ACK64#)
b. the bridge has 64-bit data that it wants to write.

These same rules apply at every cycle during the rest of the burst as well.
if  you have a 32-bit 'left-over' in your pipe-line, you do the same as
during the start of the transfer:
a. you (wait for the) end the current transfer (in this case the 64-bit
b. you start a 32-bit write, ie. you will need to re-arbitrate for the bus
to support the 32-bit transfer.

'hope this helps?

Martijn Emons
- Designer Consultant -
Arcobel ASIC Design Centre B.V.
The Netherlands
tel.:  +31 73 64 60 100
fax:  +31 73 64 60 115
----- Original Message -----
From: "Ajit Khaparde" <akhaparde@platysindia.com>
To: <pci-com-request@znyx.com>
Cc: "PCI_group COM" <pci-com@znyx.com>; "PCI_group SIG" <pci-sig@znyx.com>
Sent: Friday, November 17, 2000 9:24
Subject: Merging of two 32-bits to form one 64-bit data

> PCI Designers,
> I have come across a situation during the design of a 66MHz 64-bit
PCi-to-PCI Bridge and it goes this way....
> Case:
> The Initiator on the Primary/originating bus could be a 32-bit master and
the Target on the Secondary/Destination bus could be a 64-bit device. Then
is it possible to latch the data from the initiator as it is being
sent(32-bit) and merge two such 32-bits of data into one to form one 64-bit
of data and send it to the target, for it can accept a 64-bit transaction.
> I would like someone to comment on this and inform me whether this can be
> If yes, then I have come across one difficulty.
> If the Initiator on the primary side has sent an odd number of Double
words then my idea of merging the two 32-bits of data to one single 64-bit
could result in merging the last odd 32-bit of data with a null or stale
> Can someone suggest me a solution for this situation?
> Thanks in advance.
> Regards,
> Waiting for your reply,
> Ajit Khaparde
> Platys communications (India) Pvt. Ltd.
> Design Engineer,
> #501, Arien Apartments,
> Punjagutta,
> Hyderabad-500082,
> India
> Ph:+91-40-6507141
> _____________________________________________________________
> email for free ---> http://www.platysindia.com