I saw this mentioned here, but it would be great to have USB 3.0 support in the next version. I just ran into an issue where the Joulescope would cause a bandwidth limitation crash in the Saleae when connected to the same hub. Unfortunately, it pipes everything through the same USB 2.0 hub tree, causing the bottleneck.
I know it’s a big ask, but it would be great!
Hi @sethk - We are already working on the third-generation Joulescope JS320. It will also use USB 2 high-speed (480 MHz). We did consider USB superspeed 5 GHz with the new Infineon (formerly Cypress) FX5, but the cost add was significant compared to USB high-speed. Since Joulescopes only require about 10 MB/s, it is hard to justify a significant price increase for USB 3.
USB high-speed, full-speed, and low-speed devices are essentially on the same “shared bus” topology, where data transmission is explicitly initiated by the host. That’s just how USB 1 & 2 have worked for decades. The downside is that any device on the same root hub can reduce the amount of throughput available for other devices. While I would love Joulescopes to use USB isochronous mode, I also consider USB 2 isochronous mode to be fundamentally flawed.
USB 3 is really an entirely separate bus from USB 1 & 2 with it’s own differential pairs and signaling. The USB-IF definitely has challenges communicating port capabilities with USB 2 480 MHz, 5 GHz, 10 GHz, 20 GHz, 40 GHz, different power ratings, PPS, source/sink, battery charging, and more. That said, USB is still the easiest and most ubiquitous way to connect a peripheral to a host computer.
If you have a desktop host computer, you can add additional USB root hubs using PCIe to USB cards.
Yeah, that’s totally fair.
This is an understatement!
Unfortunately, I’m running a laptop with a dock. Thankfully, the laptop itself has 3 USB-C 3.0 ports, so I have some options when it comes to connecting. However, that defeats the whole intention behind the dock (but that’s my issue and not something Joulescope specific).
@sethk - Does the laptop have Thunderbolt? If so, then you can get a Thunderbolt dock (using PCIe) that adds more USB root hubs. You can also consider a Thunderbolt to PCIe card expander, such as the OWC Mercury Helios 3S. You can then add a PCIe to USB expansion card.
So my laptop has a Thunderbolt port, but I’m trying to minimize the number of cables I need to connect to it, which is why I got a dock. (I’m actually not sure which of the 3 USB ports is the Thunderbolt port, as the dock supposedly uses Thunderbolt and works just fine on all 3 ports….)
I’m able to solve the problem with a second USB-C cable directly to the laptop, so it’s equally inconvenient as the Thunderbolt to PCIe card expander in this case. However, I will definitely keep that in mind for my next laptop purchase (or move to desktop where I have easy expandability).
Thanks for the info and answer.
The fact that USB3 hubs don’t do transaction translation of USB 2 traffic onto the USB 3 bus has caused complaints from people trying to run multiple webcams etc, and having no way if everything goes through one root hub. I suppose the USB-IF expected serious streaming devices to go to USB3, but most manufacturers assume they’re not using “too much” of the available bandwidth and stick to USB2.
Considering the sticker price of the JouleScopes I’m surprised that USB 3 was a “significant” cost add, but I guess there’s extra R&D as well as simple chip costs.
Yeah, the fact that the USB-IF made two entirely separate buses is an annoyance. You can use USBView on Windows to see the root hub relationship. Other OS’s have similar tools.
So, every $1 of main board BOM cost is about $8 of product cost once you load on PCB cost, assembly costs, testing costs, yield, warranty, our margin, and distributor margin. The cheapest solution today that would give the same great experience is the Infineon FX5. The one we would use, CYUSB3084-FCAXI, is $19 in volume, about $15 of BOM price increase or $120 of MSRP increase.
It’s really a question of value. For most Joulescope use cases, adding USB 3 has limited utility, but we would force everyone to pay a USB 3 premium.