A simulator for the OBP space flight computer #Space #VintageComputing @hjalfi

David Given has coded an assembler and simulator for the OBP, the On-Board Processor used by a variety of spacecraft, designed way back in 1968.

The OBP is a rather elegant 18-bit, two’s-complement machine from about 1968. It’s a full Von Neumann architecture with code and data living in the same address space, of which there can be up to 64kw, divided into 4kw pages. The instruction set includes hardware multiplication and division, multiple-bit shifts, a decent set of comparison instructions, system calls, simple memory protection, rich I/O including DMA, and sixteen different individually maskable interrupts — it’s actually quite a nice thing to work with. Admittedly, running at 250kHz and with most instructions taking multiple cycles, it’s not the fastest thing around. But then it did use non-volatile core memory and was built out of raw NOR gates.

The OBP was used on a variety of spacecraft, including the OAO-3 Copernicus space telescope, which was in operation from 1972 to 1981.

See the video below and more in the article here with the code on GitHub.


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