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greatscottgadgets / cynthion

USB test instrument
https://greatscottgadgets.com/cynthion/
BSD 3-Clause "New" or "Revised" License
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question: Can Cynthion emulate a host? #174

Closed firelizzard18 closed 2 months ago

firelizzard18 commented 3 months ago

I am working on USB support for a microcontroller. When I plug my device into a PC, it does not work. I'm sure there's a bug somewhere in my descriptors or something the host OS doesn't even register that a device has been attached so wireshark is useless. To eliminate variables, I'd like to configure Cynthion to be a really basic USB host so I can plug my device in and capture and analyze the packets it sends without all the extra complexity of a full PC/OS host. Is that supported?

Zman350x commented 3 months ago

I know this isn't what you're asking, but is it even showing up in device manager at all? If not, then you probably have a bigger issue than device descriptors. It only takes a few resistors for a device to show up on your PC. Broken descriptors would just give something like "unknown USB device" or "USB error" or something like that.

firelizzard18 commented 3 months ago

I phrased the description as if I was currently working on it but in reality this is something I worked on a few years ago and recently was reminded of. I was using a microcontroller with built-in USB support. The manufacturer of the development board I used provided a C library (Arduino core) that works, but my attempt to convert that to Go failed. So I'm pretty sure I was doing something wrong, not that the microcontroller was bad. But it's been a while.

nekrondev commented 3 months ago

I'd like to configure Cynthion to be a really basic USB host so I can plug my device in and capture and analyze the packets it sends without all the extra complexity of a full PC/OS host. Is that supported?

Technically one could write gateware or a SoC firmware that would emulate an USB host. However, currently there is no support for this on the software side as far as I can see. The best for you would be to hook Cynthion up to a PC and capture the traffic between the MCU USB device and PC USB host controller and see whats going on. It's important to select the correct USB speed at Packetry before you attach the device or otherwise you won't see any packets.

firelizzard18 commented 3 months ago

Broken descriptors would just give something like "unknown USB device" or "USB error" or something like that.

This is demonstrably not true at least in Linux. When I program it (with the blinky example) via the manufacturer-provided Arduino core, it shows up in the system log (dmesg) and lsusb. When I program it with a program that has no USB support, nothing shows up in dmesg or lsusb.

miek commented 3 months ago

This is demonstrably not true at least in Linux. When I program it (with the blinky example) via the manufacturer-provided Arduino core, it shows up in the system log (dmesg) and lsusb. When I program it with a program that has no USB support, nothing shows up in dmesg or lsusb.

Most microcontrollers allow you to turn the D+/D- pull-up resistor on or off, so what probably happened is that the pull-up was disabled when running the program with no USB support and that's why you don't see anything in dmesg

miek commented 2 months ago

Closing as I think the question has been covered, but feel free to re-open if you have any more questions!