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Phases of AT type model in a system ?

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I am learning systemc/TLM2.0, I have a confusions in using the phases,

When it comes to AT modeling, BEGIN_REQ and END_REQ are used to write data from initiator to target and BEGIN_RESP and END_RESP are use to read from traget to initiator


we should split the write to target in 4 different phases and read from target in 4 different phases? I am aware of return path and early completion , i just want to have clearity on usage of request and response phases,


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BEGIN_REQ/END_REQ and BEGIN_RESP/END_RESP mark time points in the protocol. So in the stanndard implementation you have 2 phases: request and response. Depending on the type of access various data is been transferred: for a read REQ usually carries the addr while RESP carries the data and status while during a write REQ carries addess and data while RESP just carries the status. It is up to the initiator and target to care for consistency of the data in the payload, in most implementations I''ve seen the data is sampled/set at the BEGIN_* time point.

Best regards

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Okay, for more clearity ,above image is taken from LRM from section,  

1. during read command,is it 10ns in return path is for the target to perform read from  target memory  to data_pointer of initiator present in target as a part of generic payload member?  if not than when is the actual read happens ?

2.what is target doing from 110ns to 150ns ?

3.how do i interpret 5ns present in return of BEGIN_RESP

Please help .

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