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+osmo-rfds usage
+===============
+
+Flashing image
+--------------
+
+Refer to the [official documentation](https://wiki.analog.com/university/tools/pluto/users/firmware).
+
+In short, you can mount the pluto as a mass storage device, copy the
+`pluto.frm` file into it at the root, then umount and eject the device.
+
+The led should start blinking quickly, incicating the flash is in progress.
+Do **NOT** disconnect the pluto from power while this is in progress.
+Wait for it to stop blinking quickly and the new image should be ready to use.
+
+
+Connect to the pluto
+--------------------
+
+Refer to official analog wiki for full details but here are the cliff notes:
+
+* Console:
+    * `minicom -D /dev/ttyACM0`
+
+* Network :
+    * `ip link set enp0s20u3 up`
+    * `ip addr add 192.168.2.2/24 dev enp0s20u3`
+    * (replace `enp0s20u3` with whatever name the CDC ECM device was assigned on your machine)
+    * `ssh root@192.168.2.1`
+
+* Credentials: root / analog
+
+
+Running `osmo-rfds`
+-------------------
+
+Once connected, the `osmo-rfds` binary can be used to control the loopback.
+
+```
+# osmo-rfds -h
+osmo-rfds [options]
+ -t, --tx-freq
+ -r, --rx-freq
+ -T, --tx-gain
+ -R, --rx-gain
+ -s, --samplerate
+ -c, --buffer-count
+ -b, --buffer-size
+ -a, --amplitude
+ -d, --delay
+ -h, --help
+```
+
+Options should be fairly self-explanatory.
+
+ * `tx-freq` / `rx-freq` are the frequencies used, in Hz.
+ * `tx-gain` / `rx-gain` are the gain settings in dB. (Refer to iio_info for valid values)
+ * `samplerate` is the configured sample rate in Hz. 
+   This will influence the bandwidth that's echoed back as well as the delay
+   granularity. Minimum sample rate supported by IIO is ~ 2.1 Msps.
+ * `buffer-count` / `buffer-size` are advanced IIO parameters which are
+   included only for testing and should be left to their default values.
+ * `amplitude` is the scaling applied to the received signal before retransmission.
+   Beware of overflows !
+ * `delay` is the delay to be applied, in number of samples before
+   retransmitting the signal. Range is from 0 to 32767
+
+
+To do a quick test, place the pluto near an UHD device.
+
+Start the pluto relay with RX on 1G and TX on 1.1G with a 1000 samples delay:
+
+```
+# osmo-rfds -t 1100000000 -r 1000000000 -d 1000
+[+] Options :
+  . TX frequency   : 1100.000 MHz
+  . TX gain        : -40.0 dB
+  . RX frequency   : 1000.000 MHz
+  . RX gain        : 40.0 dB
+
+  . Sample Rate    : 4.000 Msps
+
+  . Buffer count   : 4
+  . Buffer size    : 4096 bytes
+
+  . Echo amplitude : 0.2
+  . Echo delay     : 1000 samples
+```
+
+
+Then start the uhd pinger to Tx on 1G and RX on 1.1G :
+
+```
+./pinger -r 1100000000 -t 1000000000
+[+] Options :
+  . TX frequency      : 1000.000 MHz
+  . TX gain           : 60.0 dB
+  . RX frequency      : 1100.000 MHz
+  . RX gain           : 60.0 dB
+
+  . Master Clock Rate : Auto
+  . Sample Rate       : 2.000 Msps
+
+  . Burst length      : 256 samples
+  . Burst period      : 250.000 ms
+  . Maximum delay     : 5.000 ms
+
+[INFO] [UHD] linux; GNU C++ version 6.4.0; Boost_106500; UHD_3.14.0.0-99-g8e7768c7
+[INFO] [B200] Detected Device: B205mini
+[INFO] [B200] Operating over USB 3.
+[INFO] [B200] Initialize CODEC control...
+[INFO] [B200] Initialize Radio control...
+[INFO] [B200] Performing register loopback test...
+[INFO] [B200] Register loopback test passed
+[INFO] [B200] Setting master clock rate selection to 'automatic'.
+[INFO] [B200] Asking for clock rate 16.000000 MHz...
+[INFO] [B200] Actually got clock rate 16.000000 MHz.
+[INFO] [B200] Asking for clock rate 32.000000 MHz...
+[INFO] [B200] Actually got clock rate 32.000000 MHz.
+[+] Echo at (0.000000, 0.000000, 159487) :
+[+] Echo at (0.098540, 615.705994, 549) : 549 (615.705994)
+[+] Echo at (0.072381, 1.956668, 583) : 583 (1.956668)
+[+] Echo at (0.073429, 2.770400, 583) : 583 (2.770400)
+[+] Echo at (0.073496, 2.343132, 583) : 583 (2.343132)
+[+] Echo at (0.072222, 2.368830, 583) : 583 (2.368830)
+[+] Echo at (0.073371, 3.440041, 583) : 583 (3.440041)
+```
+
+This shows a delay of 583 samples.
+
+If we run the pinger with RX on the same frequency as TX we get a 50 samples
+delay. So of those 583 samples, only 533 samples are due to the pluto echo.
+
+533 samples at 2 Msps = 266.5 us.
+We asked for a delay of 1000 samples at 4 Msps = 250 us.
+The additional 16.5 us represent the minimal delay due to analog delays and
+fixed processing pipelines in the pluto.
+