ISDL: An Instruction Set Description Language for retargetability and architecture exploration

We present the Instruction Set Description Language, ISDL, a machine descri ption language used to describe target architectures to a set of retargetab le design tools including compilers and simulators. Such tools enable the d esign of embedded system processors by supporting the exploration of the ar chitecture design space. The features and flexibility of ISDL enable the de scription of a wide variety of architectures with emphasis on VLIW architec tures. ISDL explicitly supports constraints that define valid operation gro upings within an instruction, thus increasing the range of specifiable arch itectures and resulting in concise and intuitive descriptions. Furthermore, a single ISDL description supports the automatic generation or retargeting of all of the design evaluation tools. This paper presents the structure and features of ISDL and describes how th e information in an ISDL description may be used to retarget or generate as semblers, disassemblers, compilers, simulators, and hardware models. In add ition, it compares ISDL to various other machine description languages that are being used for embedded processor design. Various complications that a rose while describing real-world architectures (which include a powerful se ven-way VLIW processor and the Motorola 56000 DSP) and the solutions to the se complications are also presented.