Hardware testing completed 3

Hardware testing completed

Mar

27

2011

Yes – the wire wrapped CPU prototype now passes all tests. Since I finished construction a couple of months ago I have been trying to eliminate all outstanding logic bugs and make the machine more stable. Only at this point I am confident enough to declare the preliminary QA phase completed and happily spread this ...
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Construction · General

Embarrassing flip-flop bug, again 2

Jan

26

2011

I found a nasty design bug yesterday. Some time ago, when I was approaching the end of preliminary hardware verification, having successfully completed tests for most of the instructions, I suddenly bumped into the wall. Problems occurred when I was trying to exercise my faults and interrupts mechanism. It didn’t work at all, causing the system ...
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Construction · Design

Bus-hold

Bus-hold

Dec

29

2010

There is one aspect of logic design I’ve been totally neglecting, at least until now. It is related to unconnected (floating) inputs of certain families of 74-series chips. I realized this having read a couple of articles on the web, particularly this article comparing TTL and CMOS families, this class on allaboutcircuits.com, and this paper from Texas Instruments. I am not an electrical ...
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Construction · Design

It works! 1

It works!

Dec

6

2010

Finally! It’s been 532 days (or 1 year, 5 months and 24 days) since my very first post here, and today I have a real, working machine, able to run programs and perform useful computations. Last night my CPU successfully executed the fibonacci program from this post from May (all homebrew CPU guys run fibonacci, right?). The code snippet ...
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Construction · General

Silly MDR flaw

Silly MDR flaw

Dec

5

2010

I have come across the first real design flaw in my CPU. By design flaw I mean a real design flaw, with something functioning not exactly as designed, not an accidentally swapped wire or a simple bug in schematics. The good news is that it going to be fairly easy to fix. The bad news ...
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Construction · Design

Countdown

Countdown

Nov

28

2010

I think I am ready to declare readiness for a final countdown. For the last few weeks I have been hunting for bugs in my wiring and running all sorts of unit tests. I have completed the ALU board wiring, and I think the machine is very close to successfully running some kind of useful ...
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Construction