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TimeStamps with ischo. transfers

Hi,

[First of all, this is all being done in a Kext]

I'm having some trouble with using time-stamps received with a DCL in isoch. transfers, and I would like to understand how and when they are taken.

First of all, from an earlier note in this group, I understand that the timeStamp (32 bits) format is:

SSSS SSSC CCCC CCCC CCCC OOOO OOOO OOOO

S = Second, C = Cycle, O = Offset.

And in case of isoch. time stamps, the 4 most significant bits are always going to be zero, and so are all the offset bits.

My first question is: for a Send transfer (NuDCL), if I have a group of packets/send DCLs, where I have added a timeStamp pointer only for the last packet, and also, added a callback, and an update list(with all the DCLs for this group) for this last packet, what will the timeStamp contain?

a. Will it contain the time(cycle) that the last packet (on which the timeStampPtr was adder) was sent on?

b. Or Will it contain the time that the first packet of the update list was sent on?

c. Or will it contain the time *after* the last packet was sent?

Second Question: Is the timestamping mechanism in NuDCL different from (legacy)DCL mechanism (using the take timestamp OpCode)?

The reason I ask is, that in our driver, we are using NuDCL for transmission and legacy DCL for receiving. The reason for using NuDCL for transmission is that that we needed to modify the packet length at runtime.

Any help on this matter would be appreciated.

Thanks.
Devendra.
 
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