2.3.1. Transaction Payload

The data passed in a transaction may take any form. However the TLM 2.0 standard defines a generic payload which is suitable for many uses, and which can be extended if required. By using the generic payload, a TLM 2.0 model will maximize interoperability.

The main features of the generic payload are:

Command: Is this a read or a write?
Address: What is the address (in the hardware sense of an address in memory).
Data: A pointer to the physical data as an array of bytes
Byte Enable Mask: A pointer to an array indicating which bytes of the data are valid.
Response: An indication of whether the transaction was successful, and if not the nature of the error.

Further features provide support for streaming, custom memory management and extensions to the generic payload.

A TLM 2.0 transport function is used to pass the payload to another SystemC thread and obtain a response—i.e. a transaction.

The generic payload is suitable for modeling a wide range of bus interfaces and protocols. However where additional features are required, TLM 2.0 provides an extension mechanism. The chapter on implementing a transactional JTAG debugger interface (see Chapter 11) describes the use of this extension mechanism to model the data for a bit-serial interface.