Add libusb check for known ADALM-Pluto VID:PID

[zuckschwerdt]

Some filtering and delay before letting IIO scan a USB context so we don't interfere with other drivers USB enumeration.
This should close #24.

[zuckschwerdt]

With newer libiio (version 0.24+, unreleased currently) this likely isn't needed and we add the desired VID/PID to the usb backend scan.
Since strstr() is used in older versions the VID/PID parameter is backwards compatible without the need to feature detect at runtime.
See analogdevicesinc/libiio#764 and analogdevicesinc/libiio#791

[zuckschwerdt]

To anyone able reproduce the discovery bug #24: this PR needs community testing, and some feedack, please ;)

[alphafox02]

I'll pulled and did a git checkout of this PR. This is on 20.04 and I am using the latest libad9361 and libiio pulled last night. It would appear my results are the same as master.

Here's what iio_info shows with no PlutoSDR plugged in using #50.

dragon@dragon-ROCK-Pi-X:/usr/src/SoapyPlutoSDR/build$ iio_info
Library version: 0.23 (git tag: fc3dc48)
Compiled with backends: local xml ip usb
IIO context created with local backend.
Backend version: 0.23 (git tag: fc3dc48)
Backend description string: Linux dragon-ROCK-Pi-X 5.15.0-33-generic #34~20.04.1-Ubuntu SMP Thu May 19 15:51:16 UTC 2022 x86_64
IIO context has 2 attributes:
local,kernel: 5.15.0-33-generic
uri: local:
IIO context has 1 devices:
iio:device0: axp288_adc
6 channels found:
voltage5: (input)
1 channel-specific attributes found:
attr 0: raw value: 4080
temp0: (input)
1 channel-specific attributes found:
attr 0: raw value: 976
temp1: (input)
1 channel-specific attributes found:
attr 0: raw value: 2976
current3: (input)
1 channel-specific attributes found:
attr 0: raw value: 0
temp2: (input)
1 channel-specific attributes found:
attr 0: raw value: 464
current4: (input)
1 channel-specific attributes found:
attr 0: raw value: 624
No trigger on this device
dragon@dragon-ROCK-Pi-X:/usr/src/SoapyPlutoSDR/build$

Here's SoapySDRUtil --find still seeing as though a Pluto is plugged in.

`dragon@dragon-ROCK-Pi-X:/usr/src/SoapyPlutoSDR/build$ SoapySDRUtil --find
######################################################

Soapy SDR -- the SDR abstraction library

######################################################

[INFO] [UHD] linux; GNU C++ version 9.2.1 20200304; Boost_107100; UHD_3.15.0.0-2build5
Found device 0
device = PlutoSDR
driver = plutosdr
label = PlutoSDR #0 local:
uri = local:
`

[alphafox02]

The suggestion mentioned in the other ticket about recompiling libiiio with cmake -DWITH_LOCAL_BACKEND=NO -DWITH_IIOD=NO ../) worked, SoapySDRUtil no longer sees the onboard sensor as a Pluto. That doesn't really relate to this ticket, but it works for now. I would be happy to test more suggestions or changes to this pull request, or try out different versions of libad9361 and libiio.

[zuckschwerdt]

Thanks for the detailed feedback. We'll need both PRs then. I'll update and merge #42 soon.

[alphafox02]

Would it help if I tested #42?

[zuckschwerdt]

I think #42 doesn't fit in the current source. I'll need to rewrite.

[rgetz]

This was added to libiio as analogdevicesinc/libiio#791

[zuckschwerdt]

Thanks, yes, I assume we are using that feature if available: https://github.com/pothosware/SoapyPlutoSDR/blob/master/PlutoSDR_Registration.cpp#L23-L24