[TUHS] SUN (Stanford University Network) was PC Unix
imp at bsdimp.com
Sat Apr 10 08:28:50 AEST 2021
On Fri, Apr 9, 2021 at 12:33 PM Jon Steinhart <jon at fourwinds.com> wrote:
> Lawrence Stewart writes:
> > Regarding the SUN-1 design, I had heard a rumor that it was designed
> using TTL
> > “typical” propagation delays rather than worst case, and as a result was
> > flakey.
> It's astonishing how common a practice that was back then.
Even into the 2000s. I had a 6-month long war with one of the hardware guys
for a time collection ISA card he did. It worked great, the driver worked
great. Life was good. We shipped product. 5 years later, the customer comes
back and wants a dozen more. So, we got new parts and 4 of the 6 new cards
were flakey, 2 were good. Fingers pointed at the device driver, etc. Long
months of intermittent troubleshooting continued for 5 months. During this
time I build an ISA bus trace card, showed the traces were good and the
flakiness was the result of bad data coming back from the card. At which
point they brought in a different hardware guy to look at things. He
discovered the first hardware guy had built an async circuit with typical
delay patterns. One of the parts we used was rated at 200ns, but parts from
the flakey board worked at 50ns. Turns out the manufacturer substituted a
faster part, so the 'typical' delay propagation worked for this async
circuit, but the faster response time would corrupt data from time to time.
The design was tweaked to be synchronous with a latch, and the unmodified
driver worked perfectly then...
Fun times that...
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