LimeSDR mini can't get past 480Mbps

Hi all, trying to push my LimeSDR mini to the max, I’ve been playing with sdrangel and noticed that above 14MS/s I started getting Dropped frames, at about an indicated throughput of 45.056 MB/s. That hint made me check the USB speed and indeed I found out the LimeSDR mini was connected at 480Mbps.

The strange thing is that lsusb says

SuperSpeed USB Device Capability:

  • bLength 10*
  • bDescriptorType 16*
  • bDevCapabilityType 3*
  • bmAttributes 0x00*
  • wSpeedsSupported 0x000e*
  •  Device can operate at Full Speed (12Mbps)*
  •  Device can operate at High Speed (480Mbps)*
  •  Device can operate at SuperSpeed (5Gbps)*
  • bFunctionalitySupport 2*
  •  Lowest fully-functional device speed is High Speed (480Mbps)*
  • bU1DevExitLat 10 micro seconds*
  • bU2DevExitLat 2047 micro seconds*
    Device Status: 0x0001
  • Self Powered*

which would make me think it is capable of 5Gbps, but for some reason I cannot access that speed.
In order to make sure the port on my Dell Elitebook 840 was working ok, I connected a USB3 SSD which was correctly recognized and connected at 5Gbps.

I am running Ubuntu 18.04.3 LTS and kernel is

4.15.0-58-generic #64-Ubuntu SMP Tue Aug 6 11:12:41 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Anyone has an idea about this problem and what could cause this?

matt i2eeq

Just an update about my LimeSDR mini on Windows. I have tried the LimeSDR mini on my latop, an i7 based Surface Book 2, with even worse results - SDRAngel cannot get past 9MS/s; this is very frustrating as I’ve purchased this to leverage the remarkable bandwidth.

I followed the drivers installation guids but it turned out the driver was already installed (FTDI USB 3.0 Bridge).

Is there any possibility that the unit is defective and must be returned?

Has anyone experienced anything similar?

thanks in advance

matt iz2eeq

It is already reported problems with different USB controllers (VL805 chip), front panel USB connectors, bad USB cables and insufficient power supply from lap top PC. Change cable and plug it in directly to motherboard USB 3.0 connector (detach any other USB peripheral), run LimeSuiteGui and perform tests.
FTDI offers FT601 utility for check and/or configuring USB3 bridge.

@yt7pwr thanks for hint

I guess I have finally found the problem. To mitigate the serious heating I had added a small fan (same type used for PIs) soldered to the J10 header: as soon as I removed it, LimeSDR mini was able to reach the design max bandwidth.

Interestingly enough, before removing the fan I tried to apply external power supply in terms of USB Y cable but it did not make any change. So now I am sure the fan was the problem, but I am still not sure why…

iz2eeq matt

Overheating is well known problem but you should have at least few minutes before problem starts. Anyway, you have to lubricate it well :slight_smile:

73 Goran, yt7pwr

I finally solved the problem, which was not the fan, at least not directly: it was the fan mount which had not enough clearance to allow for USB connector full insertion, hence the degraded performance. Now I’ve correctly filed the mount and the Lime SDR mini is working wonder with the small fan connected to J10 (the fan uses just 30mA).

iz2eeq matt

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