Start • The Project • C Compiler • Instruction Set • Assembler • FPGA • The Processor Interface • Datapath Resources • Datapath Schematic • Register File • Operand Selection • ALU • Result Mulitplexer • Address/PC Unit • The Datapath In Action • Development Tools • High Performance Design • References, Sources & PDF

I used to envy CPU designers—the lucky engineers with access to expensive tools and fabs. But, field-programmable gate arrays (FPGAs) have made custom-processor and integrated-system design much more accessible.

20–50-MHz FPGA CPUs are perfect for many embedded applications. They can support custom instructions and function units, and can be reconfigured to enhance system-on-chip (SoC) development, testing, debugging, and tuning. Of course, FPGA systems offer high integration, short time-to-market, low NRE costs, and easy field updates of entire systems.

FPGA CPUs may also provide new answers to old problems. Consider one system designed by Philip Freidin. During self-test, its FPGA is configured as a CPU and it runs the tests. Later the FPGA is reconfigured for normal operation as a hardwired signal processing datapath. The ephemeral CPU is free and saves money by eliminating test interfaces.