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| Simple way to show ethernet packet timing on scope |
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| mikeselectricstuff:
Once again I don't need to trigger on the packet, just see where it is relative to me reading it out of the W5500 - ideally start and end. Sounds like the encoding makes it a lot less straightforward than I expected.. |
| tautech:
--- Quote from: mikeselectricstuff on July 23, 2018, 08:24:26 pm ---Once again I don't need to trigger on the packet, just see where it is relative to me reading it out of the W5500 - ideally start and end. Sounds like the encoding makes it a lot less straightforward than I expected.. --- End quote --- What about a Period trigger ? |
| ajb:
If you were to hook up an external PHY to the same link via an ethernet hub (not a switch!) or a passive tap, scoping its RXDV signal should give you a reasonable idea. PHYs usually require minimal configuration, so it should be pretty easy to get a cheap PHY breakout PCB up and running for the purpose. You might not even have to touch the SMI. |
| Hydron:
If you can dig out another Ethernet device with a separate MAC and PHY chip, you could try passively splitting the incoming data pair to both devices and sniff the MAC->PHY connection - it should have a deterministic latency given in the datasheet and handy pins like "receive data valid" etc if you don't want to sniff the whole bus. You probably want something using the full MII interface rather than RMII, and may need to force it to not auto-negotiate or auto crossover. If that's not workable then maybe find said separate MAC/PHY device and put it on the transmit side? No need for any sketchy signal splitting etc in that case. Might get lucky and find a switch to use like that (I have an old gigabit switch here in London that has a separate PHY per port - let me know if you get desperate and I can chuck it on the scope to see what I get out in 100Mbit mode) Edit: ajb - looks like I had the same idea at the same time as you! Bit slow typing it out on the phone, and it didn't give me the desktop version's new post summary thing. |
| amyk:
Don't know which scope you have but apparently some of them can do 10M/100M Ethernet decode. 100baseTX has no long-term scrambling to speak of but uses 4B5B and MLT3 to transform the bits so you might be able to trigger on a packet start if you work out what the resulting waveform should be (start of frame is very distinctive above physical layer, it may still be just as distinctive there.) Dig into IEEE 802.3 and have a look... |
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