ISDL: An Instruction Set Description Language for Retargetability and Architecture Exploration

Wepresent the Instruction Set Description Language, ISDL, a machinedescription language used to describe target architectures toa set of retargetable design tools including compilers and simulators.Such tools enable the design of embedded system processors bysupporting the exploration of the architecture design space.The features and flexibility of ISDL enable the description ofa wide variety of architectures with emphasis on VLIW architectures.ISDL explicitly supports constraints that define valid operationgroupings within an instruction, thus increasing the range ofspecifiable architectures and resulting in concise and intuitivedescriptions. Furthermore, a single ISDL description supportsthe automatic generation or retargeting of all of the designevaluation tools. This paper presents the structure and featuresof ISDL and describes how the information in an ISDL descriptionmay be used to retarget or generate assemblers, disassemblers,compilers, simulators, and hardware models. In addition, it comparesISDL to various other machine description languages that arebeing used for embedded processor design. Various complicationsthat arose while describing real-world architectures (which includea powerful seven-way VLIW processor and the Motorola 56000 DSP)and the solutions to these complications are also presented.