ZPU (processor)
microprocessor stack machine
The ZPU is a microprocessor stack machine designed by Norwegian company Zylin AS to run supervisory code in electronic systems that include a field-programmable gate array (FPGA).
It has been designed to require very small amounts of electronic logic, making more electronic logic available for other purposes in the FPGA. To make it easily usable, it has a port of the GNU Compiler Collection. This makes it much easier to apply than CPUs without compilers. Sacrificing speed in exchange for small size, it keeps the intermediate results of calculations in memory, in a push-down stack, rather than in registers.
Zylin Corp. made the ZPU open-source in 2008.
Usage
Many electronic projects include electronic logic in an FPGA. It is wasteful to also have a microprocessor, so it is commonplace to add a CPU to the electronic logic in the FPGA. Often, a smaller, less-expensive FPGA could be used if only the CPU used less resources. This is the exact situation that the ZPU was designed to address.
The ZPU is designed to handle the miscellaneous tasks of a system that are best handled by software, for example, a user interface. The ZPU is very slow, but its small size helps to place any needed high-speed algorithm in the FPGA.
Another issue is that most CPUs for FPGAs are closed-source, available only from a particular maker of FPGAs.
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