When plugged into a well-configured Linux machine REDOUBLER will cause a message at the end of the dmesg list:
$ dmesg
[395858.273621] usb 1-1.2.2: new full-speed USB device number 15 using dwc_otg
[395858.383545] usb 1-1.2.2: New USB device found, idVendor=04b4, idProduct=c500
[395858.383582] usb 1-1.2.2: New USB device strings: Mfr=1, Product=12, SerialNumber=128
[395858.383598] usb 1-1.2.2: Product: REDOUBLER Random Number Generator
[395858.383614] usb 1-1.2.2: Manufacturer: Open Source Hardware Copyright (c) 2015 Peter Allan
[395858.383628] usb 1-1.2.2: SerialNumber: 1E0C08F0022E2400
It may be necessary to add your non-root user to the audio group to access it:
$ sudo adduser -G audio <your_username>
Assuming ALSA, it will also appear in the /dev/snd hierarchy, e.g.
$ ls -l /dev/snd/by-id
total 0
lrwxrwxrwx 1 root root 12 Mar 8 08:51 usb-Open_Source_Hardware_Copyright__c__2015_Peter_Allan_REDOUBLER_Random_Number_Generator_1E0C08F0022E2400-00 -> ../controlC1
Notice that it includes the unique serial number seen before, and is is registered as "controlC1" or card #1. If there are other sound devices, or other REDOUBLERs, they will also appear here with different card #s.
The REDOUBLER will also be recognized by arecord:
$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 1: Generat_1 [REDOUBLER Random Number Generat], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
Again, the REDOUBLER is listed as card 1.
To record some data from the REDOUBLER we refer to it as hw:1,0 where the first number is the card #. In this case
$ arecord -f dat -D hw:1,0 -d 10 > sample.wav
If arecord complains about "overruns" (eg. Raspbery Pi) then you may need an option like "--buffer-size=192000". The first 44 bytes of the wav file are the file header. After that there will be 961 bytes of mostly zeroes, which are the REDOUBLER's buffers before they are filled with random bits. If you want only random bits try
$ arecord -f dat -D hw:1,0 -d 1 | head -c +1005 > sample.bin
To listen to the white noise from the REDOUBLER, turn your speaker volume low and try
$ arecord -f dat -D hw:1,0 | aplay
Press Ctrl-C to end it.
To continuously record ALL the data produced by a REDOUBLER try something like
$ arecord -f dat -D hw:1,0 -q --max-file-time 600 --buffer-size=192000 --use-strftime /tank/temp/%Y/%m/%d/redoubler1-%H-%M-%S.wav &
All the files will have the 44-byte WAV header, but only the first will have the empty buffer. About 6TB of space will be required for a year of data. Use "disown" before closing the terminal. Other than disk space, resource use will be low.
To make things easier, some utilities are included in this directory. They need the Debian (Ubuntu, Raspian) package
$ sudo apt-get install libasound2-dev
Then
$ make
$ sudo make install
$ make clean
That creates the utility doubledown that pipes REDOUBLER data to stdout, e.g.
$ doubledown -l
Available REDOUBLERs: Card # Serial Number
1 1E0C08F0022E2400
$ doubledown -c1 -k1 | xxd
0000000: 47bd f192 c35c cc4c 982b 5332 b471 b303 G....\.L.+S2.q..
0000010: 0913 6f96 f9fa 03ea e0c6 4ab0 c11d 252a ..o.......J...%*
etc.
It also creates the filters oddbits and evenbits which select the bits from just one or the other MEM generator on the REDOUBLER. Putting it together
$ doubledown -c1 -k1024 | oddbits | ent
Entropy = 7.907466 bits per byte.
Optimum compression would reduce the size
of this 524800 byte file by 1 percent.
Chi square distribution for 524800 samples is 53993.07, and randomly
would exceed this value 0.01 percent of the times.
Arithmetic mean value of data bytes is 126.9712 (127.5 = random).
Monte Carlo value for Pi is 3.271305422 (error 4.13 percent).
Serial correlation coefficient is -0.005054 (totally uncorrelated = 0.0).
The 'make' command also creates the filter whiten which uses the chacha20 block cipher to take non-deterministic but biased, correlated, and otherwise flawed data on stdin, and produce statistically perfect random data on stdout, e.g.
$ doubledown -c1 -k1024 | whiten | rngtest
Copyright (c) 2004 by Henrique de Moraes Holschuh
This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
rngtest: starting FIPS tests...
rngtest: entropy source exhausted!
rngtest: bits received from input: 8395200
rngtest: FIPS 140-2 successes: 418
rngtest: FIPS 140-2 failures: 1
rngtest: FIPS 140-2(2001-10-10) Monobit: 0
rngtest: FIPS 140-2(2001-10-10) Poker: 0
rngtest: FIPS 140-2(2001-10-10) Runs: 1
rngtest: FIPS 140-2(2001-10-10) Long run: 0
rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
rngtest: input channel speed: (min=1.021; avg=2.023; max=1059.638)Mibits/s
rngtest: FIPS tests speed: (min=2.557; avg=5.404; max=6.137)Mibits/s
rngtest: Program run time: 5659664 microseconds
There is also a runs program that checks binary data for excessive gaps and blocks.