Transaction Level Modelling: A reflection on what TLM is and how TLMs may be classified

Transaction-level modelling (TLM) is a poorlydefined term, promising a level of abstraction like RTL (register transfer level), where the key feature is a ‘transaction’. But unlike registers, transactions are not well defined. While many feel they have an understanding of the term, indeed many are active proponents of this form of modelling, it remains elusive. Furthermore, multiple different levels of abstraction are offered in parallel under the umbrella of the term ‘TLM’. This paper will propose a definition of a transaction and a classification of the types of data contained within transactions, based on representations of the data movements that TLM involves. Our goal in writing the paper is to increase the common industry understanding of TLM concepts, which is essential if TLM is to provide efficiency gains approaching those which have been advertised for it.