XOP: a second generation fast processor for on-line use in high energy physics experiments

Processors for trigger calculations and data compression in high energy physics are characterized by a high data input capability combined with fast execution of relatively simple routines. In order to achieve the required performance it is advantageous to replace the classical computer instruction-set by microcoded instructions, the various fields of which control the internal subunits in parallel. The fast processor called ESOP is based on such a principle: the different operations are handled step by step by dedicated optimized modules under control of a central instruction unit. Thus, the arithmetic operations, address calculations, conditional checking, loop counts and next instruction evaluation all overlap in time. Based upon the experience from ESOP the architecture of a new processor "XOP" is beginning to take shape which will be faster and easier to use. In this context the most important innovations are: easy handling of operands in the arithmetic unit by means of three data buses and large data files, a powerful data addressing unit for easy handling of vectors, as well as single operands, and a very flexible logic for conditional branching. Input/Output will be made transparent through the introduction of internal fast processors, which will be used in conjunction with powerful firmware as a software debugging aid.