[Discuss-gnuradio] Two rtl2832 dongles in a GRC project

[Игорь Попов]

I try to make project with two dongles rtl2832+r820.

In
 GNU Radio Companion v3.7.6.1-58-g620817ed I made simple project with 
two equal channels containing rtl2832_source block and 
blocks_ctrlport_probe2. And I have an error. The output of programm is:
//////////////////////////////////////////////////////////////////////////////////////////////////////
Generating: "/home/igor/GRC_Projects/rtl_2832_block/top_block.py"
>>>
 Warning: This flow graph may not have flow control: no audio or RF 
hardware blocks found. Add a Misc->Throttle block to your flow graph 
to avoid CPU congestion.

Executing: "/home/igor/GRC_Projects/rtl_2832_block/top_block.py"

RTL2832 Source block configuration:
    Read length (bytes): 32768
    Buffer enabled: yes
    Buffer multiplier: 8
    Buffer size (samples): 131072
    Samples per read: 16384
    Buffer level: 50,0%
Successfully initialised demod: "ezcap EzTV"
Skipping auto-probe with custom tuner: "r820t"
Found RTL2832 device: ezcap EzTV (tuner: Rafael Micro R820T)
    Sample rate range:    900001 - 3200000 Hz
    Crystal frequency:    28800000 Hz
[r820t] Initialised (default bandwidth: 0 Hz)
RTL2832 Source block configuration:
    Read length (bytes): 32768
    Buffer enabled: yes
    Buffer multiplier: 8
    Buffer size (samples): 131072
    Samples per read: 16384
    Buffer level: 50,0%
libusb error: unknown return code [-6] (int rtl2832::demod::find_device():446) "libusb_claim_interface(devh, 0)"
Traceback (most recent call last):
  File "/home/igor/GRC_Projects/rtl_2832_block/top_block.py", line 146, in <module>
    tb = top_block()
  File "/home/igor/GRC_Projects/rtl_2832_block/top_block.py", line 105, in __init__
    if self.rtl2832_source_0.create() == False: raise Exception("Failed to create RTL2832 Source: rtl2832_source_0")
Exception: Failed to create RTL2832 Source: rtl2832_source_0
////////////////////////////////////////////////////////////////////////////////////////////////////
Separatly dongles are working properly. And if I run one project for the one dongle and one more for the second one all is OK.
Please help me to what direction I have to go.
Thank You.