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White boarding a RoadTest Review of The Microchip PoE to USB-C®︎ adapter

colporteur

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What are your expectations at connection point C?

 

I am considering pitching an application for the Microchip PoE to USB-CRegistered Power and Data Adapter RoadTest review. I completed a review of a PoE device, Raspberry Pi4B (4GB) plus POE Hat - Review and figured why not leverage the knowledge into another PoE review.

 

The drawing shows my preferred setup for the RoadTest, a Linux laptop interfacing through a PoE Injector communicating with a Raspberry Pi4B. The injector is a device I acquired to resolve an issue I discovered during the RoadTest Review The Road to Raspberry Pi4B/ PoE Hat RoadTest Review (PoE insight needed) . I want to avoid more purchases.

 

After reviewing the documentation I'm confused about my expectations at point C in the diagram. I was hoping a white board session with others might clarify my understanding. One of the opportunities I miss in my retirement is the napkin discussion with technical minds during a coffee break at work. Using a drawing scribbled on a napkin, like minds worked to offer insight into solving a problem presented at the table.

 

The Microchip PoE to USB-CRegistered Power and Data Adapter provides power and data communication path. Can someone confirm my understanding that the Microchip adapter is acting as a Ethernet to USB adapter for communication? I found reference to a LAN7800 USB driver chip while drilling down through one of the documents. I assume that means the end device (i.e. Pi would require the driver support).

 

I'm not familiar with many devices that combine USB port functions of power and communication. The brochure for the product shows a tablet connected as a device. I have an Apple tablet that can act as device but that makes it rather difficult to take measurements under varying loads. In my test scenario I'm thinking I will need a breakout cable to separate Microchip adapter power from the USB signal. As an additional test in my review, I was hoping to use a Android laptop I have as an additional device to test the endpoint. But again I would need to separate power and USB signals.

 

Questions:

What are your expectations at connection point C?

  • I like the idea to have discussions like that.

     

    My understanding would be that (at point C) you have a single USB-C interface providing power (as in USB Power delivery up to 20V 3A if the device is capable of active PD negotiation) and USB communication.

    The RPi uses the USB-C port only for power and this only for 'passive' PD with a max of 5V 3A. As the RPi is a USB host, you could not use the data part of that setup.

    I hope this makes sense.

    - W.

  • in reply to wolfgangfriedrich

    To bad we didn't have the napkin between us. Here is my confusion. I agree the Micochip device is USB-C output but it does send the data out the otherside as Ethernet or that is what I assume (maybe I am wrong). That would lead me to see the Microchip as a USB to Ethernet adapter requiring a device driver. If I am wrong how is the data sent down the wire. At the other end the data has to be removed from a PoE injector (i.e. Ethernet).

     

    I appreciate taking the time to respond. Still searching. If you wanted to talk to the end device from laptop what would the end device been identified as a USB device or an Ethernet connection? If USB what are the protocol changes between the different points A, B & C.

     

    The more research I do for the Review the more I think it is a great opportunity to answer questions. Just because there is PoE to USB when would you want to use it and at what cost.

  • in reply to colporteur

    I looked into the Quickstart guide for the Microchip adapter. It does need drivers for unit plugged into the USB port (the RPi4 in your case). And it also states that the USB port on the Microchip adapter is a USB device port so it would be possible to plug in the RPi if you have a USB splitter to separate power and data. My statement (Guess) in my 1st comment about the Micorchip adapter being a USB master port is incorrect.

    Asplitter like this might be usable:

    https://www.tindie.com/products/8086net/usb-cpwr-splitter/

    https://www.tindie.com/products/clarahobbs/pd-buddy-wye/

     

    The question still stands, as what kind of connection it would show up on the RPi? Now I would guess, it would present itself as a regular network connection through the custom driver, but not sure about this.

     

    The roadtest could be a straight functionality investigation with install instructions, performance data rate test as one part. Sounds like mostly software driver installation and IT work.

     

    The other part would be to exercise the USB PD part. A USB PD Sink would be required to request different power profiles between 5 V and 20 V with different max current settings.

    A device like this would be useful (shameles self plug image)

    https://www.tindie.com/products/pier42/usb-c-pd-sink/

     

    - W.

  • in reply to wolfgangfriedrich

    Thanks for the two adapter links. I was looking through the Internet to see if such beast exist.

     

    I'm curious about your final recommendation. It generates power out the USB-C port from a power supply connected. I would need to measure power from the PoE yes/No? What did I miss?

  • in reply to wolfgangfriedrich

    It will be a USB-LAN adapter with the LAN7800 chipset. Unfortunately, as the Pi uses the port only for power and not data, you won't be able to transact data on the LAN, but even just having USB-PD power from PoE could be valuable in some application contexts.

     

    - Gough

  • in reply to Gough Lui

      wrote:

     

    It will be a USB-LAN adapter with the LAN7800 chipset. Unfortunately, as the Pi uses the port only for power and not data, you won't be able to transact data on the LAN, but even just having USB-PD power from PoE could be valuable in some application contexts.

     

    - Gough

     

    Can someone confirm my understanding that the Microchip adapter is acting as a Ethernet to USB adapter for communication? I found reference to a LAN7800 USB driver chip while drilling down through one of the documents. I assume that means the end device (i.e. Pi would require the driver support).

     

     

    This device should be mated with te USB connector you normally use to power the Pi. It will now power the Pi. And with correct drivers, also act as a network device.

     

    The PoE hat does not have a role in this context.

  • in reply to Jan Cumps

    Funny that - I didn't realise they enabled USB-OTG on the USB-C connector. In that case, yes, the Pi would be able to detect a USB-Ethernet bridge and potentially transact data, but you do need to make a change to the boot configuration to load the necessary overlay -

    https://dev.webonomic.nl/4-ways-to-connect-your-raspberry-pi-4-to-the-internet

     

    - Gough

  • in reply to Gough Lui

    I'd have to check, but believe you don't need to enable OTG.

    That is to turn the USB-C connector into a network card when you use a plain USB cable between laptop and Pi.

     

    In this case, the Microchip PD-USB-DP60 is a network adapter. Instead of enabling OTG, you need to install correct linux drivers for the device.

    The drivers are documented via a document linked in the product home page.

    The software is available from the same page:

    https://www.microchip.com/wwwproducts/en/LAN7800#additional-features

    Documents -> Software Libraries

  • in reply to Jan Cumps

    Well, you'll have to just try it and see. The reason I say you may have to enable the overlay is because the OTG hardware on the Pi4 is configured "device only" by default -

    The OTG hardware present on previous models of Pi is still available and it has moved to a single connection on the USB-C port. The OTG hardware is intended to be used in device-only mode on Pi 4.

    from https://www.raspberrypi.org/documentation/hardware/raspberrypi/usb/README.md

     

    Instead, if you want to be able to talk to the Microchip LAN7800, you basically need the OTG port on the Pi4 (i.e. the USB-C port) to become a USB host as the adapter is very clearly a device-only role. I'm not sure if such a configuration will be stable or intended based on the documentation.

     

    But just to "try it out" is a perfectly good reason to apply for a RoadTest, because I'd have to say that some of the documentation is not quite as clear as it should be, and the way USB-C is implemented across devices is very very variable.

     

    - Gough

  • I love this site! I miss the coffee break napkin discussions at work but this site provides the ideal replacement. My thanks to & for making posts to my discussion. Your input enabled me to discover a feature of the the Raspberry Pi. I had never heard of USB OTG (On The Go) or that such a features was available on the Pi.

     

    I followed up on your posts and set out to test the Raspberry Pi USB OTG interface. I assembled a cable that would allow me to connect my laptop USB port to the Pi4B USB-C. I disconnected all peripherals from the Pi4B hoping the laptop USB port could sufficiently power the Pi.  I followed the instructions listed in the links and changed the /boot/config.txt & /boot/cmdline,txt files to enable OTG.

     

    The moment of truth, I plugged the Pi4B into the laptop and booting started. I then attempted to connect to the Pi (previously configured wireless connection) and was rewarded with success. The Pi4B booted! A quick ip a command and I discovered a usb0 interface on the Pi. I then made /etc/dhcpcd.conf configuration to determine if I could assign an IP address to the interface. That was a success also.

     

    I then got lost thinking I could connect to the interface over my network. After some head scratching I realized the errors of my ways. It is not on my network but rather a end to end connection from the laptop to the Pi.  I discovered the laptop had created an addition network interface for the usb port but had no IP configuration. I'm assuming if that interface was configured correctly I would be able to talk. I will leave that for possible RoadTest Review details.

     

    Thanks to your input I have at least one RoadTest Review scenarios to explore. I also think physical separation of data and power on a USB-C is another good investigation scenario.