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

Race conditions 2

Race conditions

Mar

21

2011

I think I am running into all kinds of logic design pitfalls possible. Although it slows me down quite a bit, I consider this an excellent educational experience. Race conditions is what hit me this time. In general a race condition is a state of a logic system in which particular logic gate temporarily outputs ...
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Design - control

My bookshelf

My bookshelf

Feb

28

2011

A while ago I told a colleague at work that I build a custom CPU in my free time. His first question was – how come I still have free time? Considering our type of work, this was the most obvious first question to ask – currently I can only spendfew hours each weekend to ...
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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