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Comment by blitmap | Hacker News Reader

This is an impressive undertaking, and hands-down one of the coolest things I have ever seen. :-)

Thank you very much! I always wanted to check out the PDP-1 and play Spacewar. Because I'm on the wrong continent, the only way to do it was to build my own :-)

There is a follow up - it can also play music, just like the original could. Check it out: https://www.youtube.com/watch?v=ROPyR-tV7A4

Kudos for such an impressive achievement (hrvach is the author of the featured PDP-1 FPGA Implementation.)

A quick question: Were the original PDP-1 manuals enough to implement the system from scratch? Were there details or hidden issues you had to "guess"?

The manuals found on Bitsavers were a great help, they are very detailed and explain the system well.

The original instruction test tapes helped me a lot with debugging the various corner cases. For example, the multiply step opcode (MUS) is re-used in later versions which had full hardware multiply (MUL). The backwards compatibility was retained by flipping a switch inside the computer to selecting between MUS and MUL. I had some programs failing mysteriously because of this.

There were also various pixel brightness available and after implementing it, I discovered Spacewar actually uses that to make some stars brighter than others.

Music playing capability was very advanced for its time (having 4 voices) and after everything was a "silent movie" for a while, there was a rewarding moment when I finally fixed a bug and Mozart started playing from the speakers.

A cool machine, very advanced for its time...

Cheers!

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