Hi,
is the Saleae (Saleae Logic Pro 16) not capable of running on USB 3 only? I need to isolated it, but with a USB 3 fiber optics cable, the Saleae is not recognized.
best regards
What fiber optic cable are you using?
Note: some cables may be uni-directional, which likely won’t work w/ Saleae logic. Also, if you want full isolation, how is the Saleae logic (device) side being powered?
Alternatively, there are USB 3 isolator devices, but make sure you get one w/ SuperSpeed (full 3.0+ spec) capability if using a Logic Pro device.
For example, see:
@x-x-xx-x-x A quick note — for our USB 3.0 models (Logic Pro 8 and Logic Pro 16), and when connected with a USB 3.0 cable to a PC’s USB 3.0 port, the device initially connects using USB 2.0 but then re-enumerates over USB 3.0.
In case your USB 3.0 fiber optics cable is not able to operate via USB 2.0, a connection will not be possible due to the above requirement.
Thank you for the clarification. Still, this is unfortunate. I would love to see a future firmware that could handle USB 3 only. this would increase the usability for tasks where good isolation is necessary, like in power electronics.
Out of curiousity (I’ve never developed USB 3.0 devices), is there a compelling reason to first connect via USB 2.0 and then re-enumerate? Is a transition to pure USB 3.0 something we can look forward to as a firmware update? Any idea when?
Good question.
The USB 2.0 to USB 3.0 transition is a side effect of the hardware boot loader that’s integrated into our USB 3 device controller. We use the Cypress (now Infineon) FX3, which has several boot options, including the option to startup and enumerate as a simple bootloader device. Our software detects this and downloads our firmware to RAM, then reboots the device. This makes firmware management very simple for us, because it means we don’t need to have a firmware update process, and we don’t need to store firmware on the device. Instead, we only store our USB identification, which only takes a few bytes. This ensures that the software & firmware versions will always match, and we don’t need to worry about downgrades or upgrades.
At the time, we never imagined the USB 2.0 requirement would be a problem. To this day, the only USB-3 only use cases we’ve seen have been these fiber optic cables. I’m surprised they exist, given that I’m pretty sure the USB 3 specification requires all USB 3.0 ports to include USB 2.0 connectivity.
We did consider moving away from this for our existing products, at least for testing, however we did not design in enough non-volatile memory to fit our firmware image. It just has enough space to fit our USB identification and other identifiers. There isn’t enough space to fit our calibration data, which is why that needs to be downloaded by the software.
For future products, we are planning to store the firmware on the device, but mainly for other reasons - like the ability to do basic functions without our software running and connected.
I’ve started looking around at Fiber Optic USB 3 cables, and at least some of them claim USB 2 and USB 3 connectivity. Can you send me the model you’re trying to use? Have you tried one that claims both USB 2 and USB 3 support?
This might be as simple as buying a different cable.
I tried this cable: Delock 66466. I am aware there are extenders with some kind of USB hub, that does USB 2 to USB 3 translation, e.g. Lindy 43363. But as far as I know this is not part of the USB specification, so it is hard to tell if it will work and they are bit too pricy to just give it a try.
Interesting! I had not seen USB 3 extenders that let you use your own fiber cable. I was just looking at cables like this:
Which carries this note:
Note: The 50 and 100 ft versions of this cable are compatible with devices that are USB 2.0 as well as USB 3.0, but it has to be plugged into a USB 3.0 port in order to function! The 30 ft is currently only compatible with USB 3.0 devices.
Do you specifically need both long distance support and isolation? Or is just isolation sufficient, for example using an isolator like this: ALLDAQ ADQ-USB 3.0-ISO-with Power Supply Unit (EU) / USB 3.0 SuperSpeed-Isolator bis 1kV, inkl. passendem 5V-Steckernetzteil EU Variante | 143382
I only need isolation, but one with low capacitance because the isolated side can experience voltage changes with a high dv/dt. Active USB cables (fiber + supply) won’t work because they are not isolated. The alldaq and similar USB isolators use a capacitive coupling for the USB 3 path, e.g. 100nF capacitors between two USB 3 redrivers. The dv/dt will cause high currents through the capacitors, which will result in fried ICs. So after replacing these ICs a view times I was hoping for an easy solution with the fiber optics only extender. Maybe I’ll build a small PCB acting as a Y-adapter so I can isolate the USB 2 path separately.