On 24/01/13 11:43, Stef wrote:> In comp.arch.embedded, > David Brown <david@westcontrol.removethisbit.com> wrote: >> On 24/01/13 00:56, Grant Edwards wrote: >>> >>> I'd have to agree with that. It looked to me like he was going to >>> have to put a 3-port Ethernet switch in every one of his widgets so he >>> could daisy-chain them (unless he can live with a star topology with a >>> switch at the center). The 10base2 thinnet solution using 50 Ohm coax >>> and BNC "T" connectors would be cute, but good luck getting parts. >>> Can you even buy PHY chips and magnetics for 10base2 these days? >> >> I don't think coax Ethernet used magnetics - it certainly did not have >> good isolation. I remember getting buzzed when connecting coax Ethernet >> cables to computers on different mains circuits. > > 10base2 does use magnetics and is isolated. On problem with that is that > the entire network cable is floating and can get statically charged, that > can zap you. I don't recall if there where cards with bleed resistors, > but each card had some over voltage protection device over the magnetics, > somewhere in the region of 1500V. > And if I think about it, I seem to remember termination resistors with a > little metal chain to ground your cable at one end. But that memory is a > bit vague. ;-) > > That chain could explain your experience: If the cable was grounded > somehere remote and you'd touch the cable BNC and the PC case, you could > have a potential difference. You would not notice this if you touched > only the BNC connector on the PC, as this was isolated. > > Main cause for voltage on a PC case are ungrounded PC's in my > experience, not difference between mains circuits (they must be quite > substantial for you to feel them). > The case of ungrounded PC's is at half the mains voltage due to the > capacitive voltage divider in the mains filter. >This sounds like a likely explanation. I don't remember the cable being grounded anywhere (at least, not intentionally!) - but I certainly touched both PC and cable while connecting them. By the time I learned the details of Ethernet hardware, we had moved over to twisted pair.
Smalles Ethernet (no TCP/IP) implementation, even 10Mbps
Started by ●January 22, 2013
Reply by ●January 24, 20132013-01-24
Reply by ●January 24, 20132013-01-24
On Thu, 24 Jan 2013 11:43:16 +0100, Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> wrote:>In comp.arch.embedded, >David Brown <david@westcontrol.removethisbit.com> wrote: >> On 24/01/13 00:56, Grant Edwards wrote: >>> >>> I'd have to agree with that. It looked to me like he was going to >>> have to put a 3-port Ethernet switch in every one of his widgets so he >>> could daisy-chain them (unless he can live with a star topology with a >>> switch at the center). The 10base2 thinnet solution using 50 Ohm coax >>> and BNC "T" connectors would be cute, but good luck getting parts. >>> Can you even buy PHY chips and magnetics for 10base2 these days? >> >> I don't think coax Ethernet used magnetics - it certainly did not have >> good isolation. I remember getting buzzed when connecting coax Ethernet >> cables to computers on different mains circuits. > >10base2 does use magnetics and is isolated. On problem with that is that >the entire network cable is floating and can get statically charged, that >can zap you. I don't recall if there where cards with bleed resistors, >but each card had some over voltage protection device over the magnetics, >somewhere in the region of 1500V. >And if I think about it, I seem to remember termination resistors with a >little metal chain to ground your cable at one end. But that memory is a >bit vague. ;-) > >That chain could explain your experience: If the cable was grounded >somehere remote and you'd touch the cable BNC and the PC case, you could >have a potential difference. You would not notice this if you touched >only the BNC connector on the PC, as this was isolated.10base2 wiring instructions required exactly _ONE_ grounding point in the network. Using more than one grounding point did cause ground loop problems.
Reply by ●January 24, 20132013-01-24
On 2013-01-23, David Brown <david.brown@removethis.hesbynett.no> wrote:> If you want to write PC code to communicate with your system, it's easy > with Linux - just open a raw socket and away you go. You can happily > use languages like Python for this to do it quickly and simply. With > Windows, life is more complicated - but it is still possible.An intesting coincidence... In my department staff meeting this morning, the engineer who is responsible for one of the Windows apps that talks raw ethernet to one of our product lines says the app doesn't work under the latest versions of Windows 8 (it did work with earlier versions of Win8). I'm sure we'll get it to work again, but everybody involved will agree that over the life of the product, choosing raw ethernet created orders of magnitude more work work than it saved. Choosing raw ethernet many years ago probably saved _one_ firmware engineer a few weeks effort. In the years since, it has probably cost several man years of extra work. According to the tech support support guys, raw ethernet is a constant source of breakage for people with any sort of third-party windows "security" software installed.> Raw Ethernet is faster, more predictable and has lower overheads than > IP - even UDP. That is why it is used for protocols like ATA over > Ethernet.For ATAoE or SCSIoE, that small overhead is important. For turning the lamp in the living room on/off, it's not. -- Grant Edwards grant.b.edwards Yow! And then we could sit at on the hoods of cars at gmail.com stop lights!
Reply by ●January 24, 20132013-01-24
On 2013-01-24, David Brown <david@westcontrol.removethisbit.com> wrote:> I didn't think about that - I've only used such programs during testing, > and it's not a big problem to use root on a development machine. But I > agree that using root for something you run often is not nice - even > with setuid or CAP_NET_RAW (if I've got that one right).I was wondering if SELinux had a capability that could fix that problem, but I don't have SELinux installed on any of my boxes, and requiring it of customers wouldn't be an option.>>> You can happily use languages like Python for this to do it quickly >>> and simply. >> >> I know. I was the one who added raw socket support to Python because I >> had to deal with the headache of troubleshooting stuff that uses raw >> Ethernet. :) > > Well, I owe you my thanks here. It made some development work I did > much easier. > > I haven't used raw Ethernet much in practice - I only used it as a > stepping stone to getting LWIP working on an MPC microcontroller. > But it was easy to set up, and easy to work with on the PC (using > Python, as root...), and let me troubleshoot my MAC setup.Using raw ethernet as a development step makes a lot of sense. Supporting it in a product is where all the headaches start.> Basically, I think that if you are communicating over Ethernet with a > PC (Windows, Linux, whatever) or other standard equipment, then IP > with UDP and/or TCP is definitely the right choice. But raw Ethernet > is quite a realistic option for a closed network between nodes that > you have full control over, and the low and predictable latencies can > fit far better in many industrial applications than UDP.If you can keep the network closed and really don't want to talk to PCs, then it may be a good option.>> The 10base2 thinnet solution using 50 Ohm coax >> and BNC "T" connectors would be cute, but good luck getting parts. >> Can you even buy PHY chips and magnetics for 10base2 these days? > > I don't think coax Ethernet used magnetics - it certainly did not > have good isolation. I remember getting buzzed when connecting coax > Ethernet cables to computers on different mains circuits.That's interesting -- I assumed there was galvanic isolation. But now that I think about it, the BNC shell always appeared to be connected directly to chassis ground. -- Grant Edwards grant.b.edwards Yow! I once decorated my at apartment entirely in ten gmail.com foot salad forks!!
Reply by ●January 24, 20132013-01-24
On 2013-01-24, Paul <paul@pcserviceselectronics.co.uk> wrote:> In article <kdptc0$4ss$1@reader1.panix.com>, invalid@invalid.invalid > says... >> >> On 2013-01-23, David Brown <david.brown@removethis.hesbynett.no> wrote: > ..... >> > With Windows, life is more complicated - but it is still possible. >> >> From what I've gathered it's rather painful and is difficult to make >> work across different windows versions. > > What isn't difficult across Windows versionsTouch� -- Grant Edwards grant.b.edwards Yow! How's the wife? at Is she at home enjoying gmail.com capitalism?
Reply by ●January 24, 20132013-01-24
In comp.arch.embedded, Grant Edwards <invalid@invalid.invalid> wrote:> On 2013-01-24, David Brown <david@westcontrol.removethisbit.com> wrote: > >>> The 10base2 thinnet solution using 50 Ohm coax >>> and BNC "T" connectors would be cute, but good luck getting parts. >>> Can you even buy PHY chips and magnetics for 10base2 these days? >> >> I don't think coax Ethernet used magnetics - it certainly did not >> have good isolation. I remember getting buzzed when connecting coax >> Ethernet cables to computers on different mains circuits. > > That's interesting -- I assumed there was galvanic isolation. But now > that I think about it, the BNC shell always appeared to be connected > directly to chassis ground.No, there was always a plastic part between case and metal shell of the BNC. See this example: http://uk.shopping.com/Longshine-LCS-8034TB/info A PCI 10base-T/10base2 combocard, still available. -- Stef (remove caps, dashes and .invalid from e-mail address to reply by mail) meetings, n.: A place where minutes are kept and hours are lost.
Reply by ●January 25, 20132013-01-25
In article <kds1t3$sbl$2@reader1.panix.com>, invalid@invalid.invalid says...> > On 2013-01-24, Paul <paul@pcserviceselectronics.co.uk> wrote: > > In article <kdptc0$4ss$1@reader1.panix.com>, invalid@invalid.invalid > > says... > >> > >> On 2013-01-23, David Brown <david.brown@removethis.hesbynett.no> wrote: > > ..... > >> > With Windows, life is more complicated - but it is still possible. > >> > >> From what I've gathered it's rather painful and is difficult to make > >> work across different windows versions. > > > > What isn't difficult across Windows versions > > Touch�But very true.... Dont even get me started on apps written in fixed pixels that are a pain on different screen sizes. Worst you have problem come up in 'safe' mode you cannot alter the settings as the dialog box is larger than screen. That is of course if the settings can be modified without full application running, which wont in safe mode. Recent case, could not uninstall a wifi driver, as the app insisted on reinstalling driver even if the device suppossedly had no power. Normal mode start system driver crash, safe mode unable to uninstall or disable! That took some doing to disable. -- Paul Carpenter | paul@pcserviceselectronics.co.uk <http://www.pcserviceselectronics.co.uk/> PC Services <http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font <http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny <http://www.badweb.org.uk/> For those web sites you hate
Reply by ●January 25, 20132013-01-25
Paul wrote:>... >Recent case, could not uninstall a wifi driver, as the app insisted on >reinstalling driver even if the device suppossedly had no power. Normal >mode start system driver crash, safe mode unable to uninstall or >disable! That took some doing to disable.In some extreme cases like that, I was forced to boot from a Linux CD, mount the windows disk and erase the offending files, (at least the ones I could identify.) Then reboot while crossing fingers ... -- Roberto Waltman [ Please reply to the group, return address is invalid ]
Reply by ●January 26, 20132013-01-26
In article <5cd5g8l9bib39vf9snsfagunqqmipkdr5e@4ax.com>, usenet@rwaltman.com says...> > Paul wrote: > >... > >Recent case, could not uninstall a wifi driver, as the app insisted on > >reinstalling driver even if the device suppossedly had no power. Normal > >mode start system driver crash, safe mode unable to uninstall or > >disable! That took some doing to disable. > > In some extreme cases like that, I was forced to boot from a Linux CD, > mount the windows disk and erase the offending files, (at least the > ones I could identify.) > Then reboot while crossing fingers ...Most Windows 'diagnostics' assume 95% of system is working first :-) -- Paul Carpenter | paul@pcserviceselectronics.co.uk <http://www.pcserviceselectronics.co.uk/> PC Services <http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font <http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny <http://www.badweb.org.uk/> For those web sites you hate
Reply by ●January 26, 20132013-01-26
On 2013-01-26, Paul <paul@pcserviceselectronics.co.uk> wrote:> In article <5cd5g8l9bib39vf9snsfagunqqmipkdr5e@4ax.com>, > usenet@rwaltman.com says... >> >> Paul wrote: >> >... >> >Recent case, could not uninstall a wifi driver, as the app insisted on >> >reinstalling driver even if the device suppossedly had no power. Normal >> >mode start system driver crash, safe mode unable to uninstall or >> >disable! That took some doing to disable. >> >> In some extreme cases like that, I was forced to boot from a Linux CD, >> mount the windows disk and erase the offending files, (at least the >> ones I could identify.) >> Then reboot while crossing fingers ... > > Most Windows 'diagnostics' assume 95% of system is working first :-)And they're useless for the other 5%. -- Grant Edwards grant.b.edwards Yow! I have a VISION! It's at a RANCID double-FISHWICH on gmail.com an ENRICHED BUN!!
