Hacker News Reader

Comment by cnvogel | Hacker News Reader

Probably out of fear that the signals might deteriorate with probes attached.

But with a modern-ish logic-analyzer and the ancient original hardware (huge voltage swings, slow clock, very long busses), I doubt that the probes would make a discernible difference, would they?

View on HN

Yes, you're right about the signals. The Alto has a 5.88 MHz clock which is very slow by modern standards, and the buses are a couple feet of wire-wrapped pins so the probes are unlikely to have any effect.

I'm not sure modern-ish is the right word for the logic analyzer. It's a 1999 Agilent logic analyzer and I don't know how they managed to make it so slow. You can ftp a trace off it over Ethernet at the glacial speed of 10 kilobytes per second, so copying traces for analysis is a big bottleneck.

Is it a 16500? If so, you might see if you can scrounge up a 16505A, which might be able to network much faster (plus, it supports VNC and has a nice (for the time) graphical display. The 16505A is basically a PA-RISC pizza box that hooks up to the 16500 via a SCSI cable on the back, and adds some X11/Motif GUI happiness on top. I took a quick look around eBay and saw one for ~$275, but you might be able to get one cheaper if you look.

Side note: it was called a "Prototype Analyzer" because it was meant for analyzing prototypes, but we had more than one customer tell their salesperson to come back later when it was out of the prototype stage.

The logic analyzer is a 1670G; Marc collects vintage HP equipment, although technically this is Agilent.

You might try mounting it via NFS; it's also quite possible that the serial port might be faster for getting traces off the box than its relatively anemic ethernet support.

The serial port is also slow as molasses. If we want a full download, Marc will run it over the serial port overnight. We haven't tried NFS.

Eh, 1999 was right when the split happened, so regardless of the label, it was still basically an HP product at the time. Still, that doesn't help you much; the 16505A only worked with the 16500 series analyzer. There was a 16700, IIRC, that was basically an 16500C with an integrated 16505A, but that doesn't help you much.

Have you tried a different ethernet switch connected to the logic analyzer ? One cause of really slow transfers is one end getting the full/half duplex negotiation wrong.

That's a brilliant idea, I almost forgot about this. When I installed networking gear in the 90s, common knowledge/best practice was to always fix duplex/link-speed on fixed installed gear (routers/switches) because they frequently messed up autonegotiation.

Try a managed switch where you can choose 10/100, Full/Half and see statistics. Also try to get a "netstat/ifstat" like display on the logic analyzer to see bad packets/collisions/...

Reminds me of my electronics R&D days on flight sims in the 1980s where the fix for one particularly edge-case timing issue was to replace a 74S TTL part (within a sea of 74S logic) with a 74LS one and INSIST that only 74LS parts were used in that particular socket. Job done, no need for more probing!

Back in the old days, we saw crosstalk at at 4Mhz. I think circuits absent a pullup can be susceptible. But in general, I agree, you're more likely to break something removing and reinstalling the probes.

Which reminds me, one time back at my first job, the hardware guys were working on a new design, and it only worked with the logic analyzer probes attached to the CPU. They later discovered a missing connection between a pullup or pulldown resistor and the appropriate +Vcc or GND supply.

Reply on news.ycombinator.com