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Macintosh Plus becomes unstable ONLY when networking?


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I’m trying to get a Mac Plus connected to the Internet and surf the WWW. Actually, I have it all working... kinda. Using MacWeb and a Proxy I can browse some sites, however, the Mac will eventually freeze up. If I only just load a simple site and then quit MacWeb before it freezes, I will quickly get a bomb or freeze when trying to do something else (like opening another application). If I open any other application that requires TCP I get similar symptoms. 

 

Symptoms:

* Cursor will turn into a plain pointer and system will be completely unresponsive.

* Bombs with somewhat random errors like “invalid instruction” or “address error”

 

Setup:

* Mac Plus 4MB RAM,  analog board recapped a couple years ago.

* Asante Mini EN/SC 10T Adapter hooked up with a Raspberry Pi running OpenWRT throttled to dialup speeds with the Ethernet port set to 10T mode

~ OR ~

* Serial connection with SLiRP + MacPPP

* (My WIP proxy if you’re interested: https://github.com/danielscottjames/68kproxy)

 

Troubleshooting

* Using a serial cable to rule out any problems with the Asante adapter/drivers

* When using the serial cable I can use MacTerminal to connect to the pi and that by itself does not cause the problems

* I’ve tried various versions of OS/MacTCP/etc... at this point I think it’s not a software problem, though I’m willing to be proven wrong.

* I can launch an app that enables TCP and then ping the Plus for seeming forever, but as soon as I try to do something from the Plus then it freezes.

 

 

So, I think I’m going to have to open the Mac up and fix a hardware problem, but I’m not even sure what I should be looking for. This is a very strange problem because:

* Nothing else I’ve done with this Plus causes it to freeze/bomb like this. 

* The problems seem to ONLY happen after TCP has been loaded.

 

If anyone has any ideas I’m all ears, because I’m a couple weeks into this and going crazy (though that’s the hobby I guess)

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  • 68kMLA Supporter

What system version?  I’m sure you’ve tried running with other extensions/INITs off?  I will say both of my usual Macs (an SE/30 with Asante EN/SC and a 550c) experience random freezes when hooked up to the network, including at boot time or when opening TCP-aware applications like Fetch.  They seem to usually be correlated with random failures by my GL iNet OpenWRT router (my Mac repeatably freezes, I notice the 5G light on my router isn’t blinking as it should, I power cycle the router, everything works fine again for a few days), but sometimes there are inexplicable temporary freezes ... meaning if I wait maybe 5 minutes the Mac recovers.  I haven’t bothered to investigate much because net access is an occasional thing for me (just for software transfers really) so will be interested to hear what you learn, but I probably wouldn’t assume a hardware problem with your Plus given what you’ve described.

 

If you can, it might be helpful to run Macsbug and see what the Mac is doing when it freezes.  Is it just stuck in an infinite loop?  If so it’s more probably a software issue.

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MacTest looked promising and a lot better than Apple Personal Diagnostics until I realized it wouldn’t run on on a 6800. The personal diagnostics has a RAM/VRAM/Logic Board test that I’ve looped for 30+ minutes without finding any problems.

————————————

I’ve been trying this with system 7.0.1 and 7.1 

And I have tried disabling other extensions, in fact, I’ve tried just doing a new install with the minimum amount of software necessary to test this.

 

Macsbug looks really interesting! I will play around with that and see if it sheds any light on the freezes.

It’s a little discouraging that you have freezes, too... maybe a modern network is throwing packets around that the old software doesn’t know what to do with...

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20 hours ago, Daniel James said:

MacTest looked promising and a lot better than Apple Personal Diagnostics until I realized it wouldn’t run on on a 6800. 


MacTest definitely runs on the 68k, it goes back pretty far. Make sure you have the right version. 

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On 3/6/2021 at 11:07 PM, Daniel James said:

Serial connection with SLiRP + MacPPP

 

MacPPP doesn't support SLiRP, it supports PPP. They're two different protocols that do two different things.

 

FWIW, MacTCP and MacPPP work fine for me under 7.0.1 using PPP over null modem, but I have to use 9600 as the serial baud rate because any faster means the CPU can't keep up and drops characters. This can cause system bombs if enough information is lost in the packet.

 

It also works fine with 2400 baud on NetZero, though that's not relevant here unless you decide to go for dialup.

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I think you mean SLIP, I’m referring to this SLiRP in particular, ex: http://manpages.ubuntu.com/manpages/xenial/man1/slirp.1.html Which is capable of emulating PPP or SLIP.

 

But yeah, I’ve heard that 9600 is the max that will work so that’s what I’ve been trying. The serial connection works great as long as I’m not using it with MacTCP, I was not able to get the machine to crash when just transferring data back and forth with MacTerminal.

 

19 hours ago, nkeck72 said:

This can cause system bombs if enough information is lost in the packet.

This was my first thought when I started this, was that I was pushing too much data and overflowing a buffer and overwriting system memory. However, the more I play with it, the more it seems like as soon as MacTCP is initialized something breaks and a crash is inevitable. 

 

 

On 3/7/2021 at 2:30 PM, SuperSVGA said:

MacTest definitely runs on the 68k, it goes back pretty far. Make sure you have the right version

Sorry I wasn’t clear here, I did find a version of MacTest that ran on the Plus. However, it was not the full suite (which looks very useful) but appeared to just be a rebranding of the older Apple Personal Diagnostics. 

 

MacsBug is another dead end so far. I can not find an old enough version to run on the Plus. I suspect I could find one indirectly with some old dev kit bundle, but so far I’ve been empty handed.

 

——————————————

 

My current theory is: the ROM is mildly corrupt and MacTCP just happens to use a routine that’s corrupted that most programs do not hit. However, if that was the case I’d think it’s pretty spectacular as I’d assume ROM corruption would usually cause much more severe problems.

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  • 2 months later...
On 3/10/2021 at 5:56 PM, Daniel James said:

...I did find a version of MacTest that ran on the Plus. However, it was not the full suite (which looks very useful) but appeared to just be a rebranding of the older Apple Personal Diagnostics. 

 

I cannot find the original "MacTest" on Macintosh Garden or the Repository.  I can only find later versions like MacTest SE.  Surely someone must have posted the full suite somewhere, right?

 

This Apple document describes how to use it and shows screenshots:

https://drive.google.com/file/d/1_W0T1GJbabKm-uNPtKorivhOd21szgSW/view?usp=sharing

 

 

 

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