I received the three prototype USB 3.0 hubs for the Jetson yesterday and was able to test them this morning. Things started out great. The hub mounted onto the Jetduino and the Jetson without any problems. I was able to power it up and connect it to the Jetsons USB port, and then tested it with multiple different devices. It recognized them all and I could use them, including USB cameras, Keyboard and mouse, USB flash sticks, and external hard drives. Figure 1 shows an image of the hub mounted on the Jetduino, and figure 2 shows it mounted directly onto the Jetson. I am using a 5V @ 1A power supply for it.
Next, I went on to test the transfer speeds for the new hub, and that is where I ran into trouble. I ran a series of tests so I could compare the read and write speeds under different conditions. Before beginning I enabled the USB 3.0 capabilities on the Jetson. All tests were run using a new PNY 32GB Turbo Attache USB 3.0 flash drive on the Jetson TK1. The same USB 3.0 cable was used for all tests that required one. Write/Read speeds were tested using the following commands after cd'ing into the mounted flash drive:
> dd if=/dev/zero of=./largefile bs=8k count=1000
> sudo sh -c "sync && echo 3 > /proc/sys/vm/drop_caches"
> dd if=./largefile of=/dev/null bs=8k
The first test I performed was by connecting the flash drive directly into the USB 3.0 port on the Jetson.
Direct Connection Speeds
Write Speed: 51.8 MB/s
Read Speed: 65.5 MB/s
The second test was done using a Cypress 3.0 USB hub
Write Speed: (82 MB) copied, 4.25992 s, 19.2 MB/s
Read Speed: (82 MB) copied, 1.29301 s, 63.4 MB/s
The third test was done using the Jetson USB hub
Write Speed: (82 MB) copied, 5.94309 s, 13.8 MB/s
Read Speed: (82 MB) copied, 2.98313 s, 27.5 MB/s
As you can see, the read speed using the Jetson hub I had built was significantly slower compared to either the direct connection, or through the other test hub. Surprisingly, the write speed on the other hub was quite a bit lower as well compared to the direct connection. It was only a bit faster than the Jetson hub results.
These results are quite disappointing to me. When I started working with the manufacturer I was assured that their design was fully USB 3.0 SuperSpeed compliant, and had been used by a number of different customers without issue. I have sent an email to them detailing what I have found, and they said they will run some tests on their end. It is possible that something was messed up while they rearranged things to meet my new layout requirements. USB 3.0 devices are sensitive to board layout, and require fairly precise impedance matching to reach their full capability. That is the main reason I decided to use another companies existing design instead of trying to build this board myself. I did a decent amount of research into what would be required to make a USB 3.0 hub and decided it was over my head.
However, another other possibility is that their design was never able to attain SuperSpeed, and they were counting on most people to consider it good enough. If they are unable to find a fix for this issue then I would need to start this process all over again with a different company and try to find some way to verify their design up front.
Before proceeding with that I would like to get a better idea of what the actual demand is for this hub. For me personally, this is something I would really like to have, but it is not something that I must have for the robotics work I am planning. I know a few others have also said they are very interested in it as well. To make it even more appealing, I also planned to have some small plastic clips manufactured so you could also mount this on the Jetson TX1. My question though, is how many people would want one of these? Is it just a small subset of people, or is there a larger group out there that would be interested in this? I was originally looking to sell just the board for about $20. If you wanted one of the small USB cables and a power supply that would add $5-10 on that.
If you are interested in this hub then please leave a comment below, or email me so I can get an idea of what type of interest there is for this product. If the manufacturer cannot fix their issue, and there is not a lot of stated interest in it, then I will probably shelve this hub for the moment so I can focus exclusively on the Jetduino.
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