RE: Minor TLM enhancements/fixes

Stuart,

The issue I had in mind is that a current initiator model is not compatible with a target model assuming the new rules. In this case the initiator may send out a payload with streaming_width/byte_enables set and ignore the response, but the target may have acted on the byte_enables that it saw and produced a different result than the initiator expects.

Bart

From: Stuart Swan [mailto:stuart@cadence.com]
Sent: Friday, December 03, 2010 12:16 AM
To: Bart Vanthournout; Jerome CORNET; Bishnupriya Bhattacharya; john.aynsley@doulos.com; P1666 Technical WG
Subject: RE: Minor TLM enhancements/fixes

Bart-

A comment/question below.
Thanks
Stuart

From: owner-systemc-p1666-technical@eda.org [mailto:owner-systemc-p1666-technical@eda.org] On Behalf Of Bart Vanthournout
Sent: Thursday, December 02, 2010 9:48 AM
To: Jerome CORNET; Bart Vanthournout; Bishnupriya Bhattacharya; john.aynsley@doulos.com; P1666 Technical WG
Subject: RE: Minor TLM enhancements/fixes

Regarding 12.3.4.o): here there is a change to the standard; there is an expectation that if an initiator uses byte_enables that it can rely on the response_status. This is an issue for initiators that reuse a payload from a previous transport call, in this case streaming_width or byte_enables might have been set, causing an incompatibility with the extended rule. Rule 12.3.4.p) states that reuse of payloads is allowed, this would no longer be the case (or at least it would have different implications than today).
I would not want to make this change, in this case because of the potential backward compatibility issues.

[Stuart] Maybe I'm misunderstanding the scenario you are outlining, but if a user is writing a _new_ model that is now going to check response_status, then surely it is reasonable to say that that user should also reset the byte enable and streaming width parameters if the model is reusing payloads from previous call (and good programming practice in any case). For existing TLM2 models written to the old version of the standard , there is no effect on backward compatibility it seems to me.

Bart

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