Completely replace SD Card? (duet ethernet)



  • 20 enough?I've seen all the advice, but since I have a signal strength that flaps between -50 and -70 I'll wait till that is stable before passing judgement.. at the moment I'm happy to continue blaming my end of the network.


  • administrators

    With the signal strength changing that much, I suspect you are getting interference from another device in the same band. Have you tried changing the WiFi channel?



  • Just found something odd. I have near identical printers setup, one which has a Duet Wifi, and one which is a Duet Ethernet. Using DWC to upload a 30MB file shows the performance is severely different between the two, but not in a way that I would expect. The Wifi connected Duet can be uploaded to significantly quicker. The Duet Wifi seems to top out at around 580k/sec, whereas the Ethernet only gets to about 340k/s. Could this be a feature of the firmware on the Ethernet version? Does anyone else have similar results?

    The SD card in both is a brand new 16GB SanDisk Ultra SDHC Class 10.


  • administrators

    @spoonunit are both SD cards formatted with 64 KB blocks? That can make a difference.


  • administrators

    You can run M39 to check the cluster size.

    The other thing that can make a difference is fragmentation of the SD card. A heavily-fragmented SD card tends to slow down the speed of writing to it.

    In my tests, both WiFi (with a good signal strength)and Ethernet top out at about 1Mbps if the SD card has a large cluster size and is not heavily fragmented. For very large files it drops to around 800kbytes/sec.



  • Will double check. Both were straight out the packet, so I assume they're identically formatted. Assumptions can be wrong though.


  • administrators

    It may be worth checking that the Ethernet physical link has connected at 100Mbps, not 10Mbps.



  • Ethernet machine

    M39
    SD card in slot 0: capacity 15.93Gb, free space 15.89Gb, speed 20.00MBytes/sec, cluster size 32kb

    Wifi Machine

    M39
    SD card in slot 0: capacity 15.93Gb, free space 15.92Gb, speed 20.00MBytes/sec, cluster size 32kb



  • @dc42 Is there M command to check link speed established?

    M552
    Network is enabled, configured IP address: 0.0.0.0, actual IP address: 192.168.XXX.155

    Looking at the router, the 100M light is lit. The cable went from duet to cable to a connector on the back of the box. I've plugged the cable in directly to the Duet to rule out that short cable, but the longer cable could in theory still be to blame.


  • administrators

    @spoonunit said in Completely replace SD Card? (duet ethernet):

    @dc42 Is there M command to check link speed established?

    Not yet, but I'll add it to the network section of the M122 report in the forthcoming 2.02beta1 release.



  • I ran some more tests to see if I could find an issue with the networking but ultimately it seems fine.

    For clarity, when I originally reported the issue, I had the Duet connected to a short extension which provides an ethernet port at the back of the box. From there a cable to 10/100 switch (with a light on signifying that the Duet has a 100 link). The switch then goes to a power-line network plug, which then emerges into another switch and finally to the PC where I was testing.

    To rule out all the gubbins in the middle, I took a laptop to the room with the printer in, took out the cable from the back of the printer and plugged it into the laptop. I then ran a speedtest to just check what throughput the cable should be able to receive through the powerline networking. It's less than stellar to be honest, but even so it can get 28Mbps, or about 3MB/s which should be more than enough to pump the full potential 660K/s that I see the wireless Duet able to pull.

    Next stop was to take the powerline networking out of the equation, so I configured the laptop as a wireless bridge. I then connected the laptop directly to the printer and over that single cable still found the upload restricted, whether accessed directly from the laptop (single cable), or over the bridged networking.

    It's not a huge issue really; uploads still work. I just feel they should be much faster on ethernet than wireless, but definitely at least equal. A 100Mbps link ought to be able to copy in at 10MB/s or more, but I guess there are constraints with the electronics, firmware, and SD card that are constraining that. Will the new Duet boards in development offer higher throughput from ethernet?


  • administrators

    The major speed constraint is writing to the SD card using limited buffer space. During testing of the Duet WiFi in 2016 I found that if I had the firmware throw the data away after receiving it, I could "upload" to it at 3Mbytes/sec. That dropped to less than 1Mbyte/sec when the data was saved to SD card. What's really needed is a much larger RAM buffer, because SD cards are optimised for very large block writes as happens in digital cameras. The next-generation Duet will have more RAM. Meanwhile, now that we are using RTOS we may in a future firmware release be able to overlap SD card writing with Ethernet or WiFi receiving to a greater extent than we do now, and get some speedup that way.


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