In the old days — we are speaking like the 1960s as well as 1970s — computers were frequently developed for extremely specific functions utilizing either discrete logic or “bit slice” chips. Either way, more bits meant more money so often these computers were made with just sufficient bits to satisfy a needed precision. We don’t believe that was what was on [Mad Ned’s] mind, though, when he decided to implement a 9-bit CPU called QIXOTE-1 on an FPGA.
Like many pastime projects, this started with an FPGA board in browse of a problem. At first, [Ned] had a plan to produce a custom computer together with a custom language to then create a video game. A quick browse on the Web led to that being a typical sufficient job with one guy that we’ve talked about right here on Hackaday before knocking it out of the park.
[Ned] then believed about just doing a no-software video game. as well late to be the very first to do that. Not to be deterred, he decided to duplicate the PDP-8. Whoops. That’s been done before, too. wanting something original, he lastly decided on a custom CPU. since bytes are usually — if not technically — 8 bits, this CPU phone calls its 9-bit words nonads as well as utilizes octal which maps well to three digits per nonad.
This very first publish talks about the story behind the CPU as well as provides a short overview of its capabilities, however we are waiting on future posts to show more of what’s behind the curtain in what [Ned] phone calls “Holy Nonads, part 010.”
The drawback to doing a custom CPU is you have to develop your own tools. You can always, of course, duplicate something as well as take your toolchain. Or go universal.