Added totorial to use the AES67 Daemon on a board to operate as AES67 USB Receiver and Transmitter.

Minor changes to daemon prerequisite.

README.md

@@ -85,12 +85,12 @@ This directory contains a the daemon configuration and status files used to run
 <a name="prerequisite"></a>
 The daemon and the demo have been tested with **Ubuntu 18.04** distro on **ARMv7** and with **Ubuntu 18.04, 19.10 and 20.04** distros on **x86** using:
 
-* Linux kernel version >= 4.14.x
+* Linux kernel version >= 4.10.x
-* GCC  version >= 7.4 / clang >= 6.0.0 (C++17 support required)
+* GCC  version >= 7.x / clang >= 6.x (C++17 support required)
-* cmake version >= 3.10.2
+* cmake version >= 3.7
 * node version >= 8.10.0
 * npm version >= 3.5.2
-* boost libraries version >= 1.65.1
+* boost libraries version >= 1.65
 * Avahi service discovery (if enabled) >= 0.7
 
 The BeagleBone® Black board with ARM Cortex-A8 32-Bit processor was used for testing on ARMv7.
@@ -145,6 +145,9 @@ The demo performs the following operations:
 ## Devices and interoperability tests ##
 See [Devices and interoperability tests with the AES67 daemon](DEVICES.md)
 
+## AES67 USB Receiver and Transmitter ##
+See [Use your board as AES67 USB Receiver and Transmitter](USB_GADGET.md)
+
 ## Notes ##
 <a name="notes"></a>
 

USB_GADGET.md

@@ -0,0 +1,69 @@
+# AES67 USB Receiver and Transmitter #
+
+This document describes how to use the AES67 Daemon on a board to operate as AES67 USB Receiver and Transmitter.
+
+The board doesn't need to have an audio codec but a USB client or OTG connector that is able to operate in device mode.
+
+Eventually you will connect your card to your PC (*Windows* / *Linux* / *MAC*) via USB and use the PC as a player or recorder and the card to relay audio from USB to Ethernet and vice versa.
+
+## Kernel configuration ##
+<a name="kernel_config"></a>
+You need to enable support for USB gadget and compile and enable the USB Audio Gadget 1.0 module of the Linux Kernel. 
+For this make sure you have the following kernel config options enabled:
+
+      CONFIG_USB_F_UAC1=m
+      CONFIG_USB_CONFIGFS_F_UAC1=y
+      CONFIG_GADGET_UAC1=y
+In the Kernel menu config the location of these option is:
+
+      -> Device Drivers 
+        -> USB support (USB\_SUPPORT [=y])
+          -> USB Gadget Support (USB\_GADGET [=y])
+Transfer the new kernel and modules to the board. 
+Also make sure your board is properly configured to use the USB connector in device mode.
+
+**_NOTE:_** The reason for configuring USB Audio Gadget 1.0 instead of 2.0 is that 2.0 does not currently work properly with *Windows*.
+
+## Install the USB Audio Gadget 1.0 ##
+<a name="g_audio_install"></a>
+Install the Audio Gadget module with:
+
+      sudo modprobe g\_audio
+
+If the negotiation with the connected PC is succefull on the board a new virtual audio card shows up.
+To verify run:
+
+      cat /proc/asound/card
+The expected output is:
+
+       0 [UAC1Gadget     ]: UAC1_Gadget - UAC1_Gadget
+                            UAC1_Gadget 0
+By default this new audio codec works with a sample rate of 48Khz, 2 channels and sample format *S16_LE*.
+
+On the PC new audio input and output devices show up. 
+The name assigned to these depend on the OS.
+On *Windows* a new speaker and microphone named *AC interface* get configured.
+
+
+## AES67 USB Transmitter ##
+<a name="usb_transmitter"></a>
+Before starting make sure that the [AES67 daemon basic setup](DEVICES.ms#daemon_setup) is done.
+
+On the board run the following command to relay the audio from the USB to the AES67 Source:
+
+      sudo nice -n -10 ./alsaloop -c 2 -r 48000 -f S16_LE -C plughw:UAC1Gadget -P plughw:RAVENNA
+On the PC start the audio playback on the new device.
+
+**_NOTE:_** The *ALSA RAVENNA driver* will perform the format conversion from *S16\_LE* to the *Source* format.
+
+## AES67 USB Receiver ##
+<a name="usb_receiver"></a>
+Before starting make sure that the [AES67 daemon basic setup](DEVICES.ms#daemon_setup) is done. 
+You also need to configure a new stereo *Sink* on the daemon.
+
+On the board run the following command to relay the audio from AES67 Sink to the USB:
+
+      sudo nice -n -10 ./alsaloop -c 2 -r 48000 -f S16\_LE -P plughw:RAVENNA -C plughw:UAC1Gadget
+On the PC start the audio recording on the new device.
+
+**_NOTE:_** The *ALSA RAVENNA driver* will perform the format conversion from *S16\_LE* to the *Sink* format.