[sdiy] Analysis of the TB-303 CPU timing
davebr at modularsynthesis.com
Tue Mar 21 01:45:45 CET 2017
This thread reminds me of my early work in the 70's. The Tektronix
4112/4114 intelligent graphic terminals were all written in PL/M. I did the
disk system and wrote all the drivers in assembly which was most likely
cross assembled on a DEC 11/45. Later we used some of the Intel development
systems. One of my tasks was to rewrite some of the PL/M modules in
assembler to either compress size or speed them up. I did a lot of that for
about a year.
Previously I designed the 8080 processor system for the Tektronix 4024/4025
business graphic computer. That was all written in assembler. I later
repurposed the CPU and made a Sol-20 compatible home computer from it.
There is a photo of that on my website. When I outgrew dual cassette tapes
I moved to CP/M. Since CP/M wasn't available on the Sol-20 I had to
disassemble CP/M and then modify it appropriately. I did a lot of
disassembly in those days.
I did have a challenge on a program called Music that ran on the Sol-20. It
was a music compiler that generated three voice harmonies by creating
self-modifying code that executed in RAM. It was really bizarre but worked
quite well. I ended up disassembling and modifying that code into an
8080-based doorbell that I built probably in 1976 or 1977. I still have it
as a doorbell and it has been running in a tight loop waiting for someone to
push my doorbell for 40 years. At probably about a 16 uS loop, that loop
has executed nearly 7.8x10^13 times. That's a bunch. The 2708 eprom has
also lasted 40 years.
David J. Brown
Modular Synthesis, LLC
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