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1) USB Host and USB OTG on an android device would require the same type of cable? I.e. 4&5 pins shortened?
USB OTG components of an Android device are used to switch the USB OTG-capable Android device in USB host mode or in USB peripheral mode.
USB is a master-slave communication bus: USB communication can only take place between a master device and a slave device.
A master, or USB host, is a computer.
A slave, or USB peripheral, can be a mouse, a keyboard, a DAC, a telephone, a smartphone, a tablet …
USB was designed to be easy to use: plug-and-play!
When a user connects a USB peripheral (for example a USB DAC) to a USB host (for example a PC), the USB host’s operating system (for example Windows or Linux) detects the USB peripheral and loads the appropriate software driver (for example a USB DAC driver or USB audio driver).
More and more smart peripherals, like smartphones or tablets, have all the features of a computer.
For example, Android smartphones or tablets are Linux-based computers.
Android relies on Linux for core system services such as security, memory management, process management, network stack, and driver model.
Thus Android handles all the things that Linux is really good at such as a vast array of device drivers, which take the pain out of interfacing to peripheral hardware.
As legacy computers, legacy peripherals like Android smartphones or tablets having all the features of a computer need to interconnect with peripherals. This slave-to-slave communication functionality is not supported by the master-to-slave communication USB model.
To address this need, the USB OTG concept is added to the USB standard in 2009.
USB OTG retains the legacy master-to-slave or USB host-to-USB peripheral communication model.
A USB OTG device is a dual-role USB device, sometimes a USB host, sometimes a USB peripheral:
. a USB OTG-capable Android device operating as a USB peripheral can interwork with a PC operating as a USB host
. a USB OTG-capable Android device operating as a USB host can interwork with a USB DAC always operating as a USB peripheral.
When the (functional) Micro-A plug (i.e. pin 4 & pin 5 connected) of a so-called USB OTG cable is inserted into the Micro-USB receptacle of a USB OTG-capable Android device, the ID resistance is less than 10Ω, and the Android device is configured to USB host mode by USB OTG components.
2) Isn't it true that in addition to supporting USB Host mode, the android device must support specific USB device types to work with them?
Yes, in addition to support USB host feature, the Android device, like the PC, must support specific USB device drivers to work with them.
http://developer.android.com/guide/topics/connectivity/usb/index.html
http://developer.android.com/reference/android/hardware/usb/UsbConstants.html
E.g. to work with a USB DAC/Sound Card out of the box, the device must support USB Audio class of devices? Because this is exactly what is shown in the picture with Sony Xperia Z and Sony portabe headphone DAC/Amp: the "Z" series support USB audio device class out of the box.
Yes, to work with a USB DAC/Sound Card out of the box, the device must support USB Audio class of devices.
"Well, the USB Audio issue feels like it could've belonged at LG, or Asus or whoever the maker of each specific device happens to be.
It's the OEMs and platform vendors that actually implement the USB Audio support (I happened to be involved in this when I was at Sony Mobile).
Google (as of Android 4.1) essentially just provides some of the
higher-level mechanisms for detection of USB Audio accessories, while the OEM / platform vendor fills in the blanks. Those blanks can either be very small if you only want audio output at a fixed sample rate, or they can grow quite big if you want more features like recording, voice calls, etc.
You could argue that Google should provide a complete basic solution for USB Audio, but that's not the setup today."
http://music.columbia.edu/pipermail/andraudio/2013-May/000833.html
A request to Google for supporting USB audio is ongoing:
http://www.head-fi.org/t/595071/android-phones-and-usb-dacs/2625#post_9614979
3) Does UARP add such support to Android devices which do not natively support USB Audio device class?
Yes, if these Android devices support full USB host and support the Android USB host API.
4) How can one figure out, whether the claimed support of USB Host functionnality is sufficient for UARP/USB DAC combo operation, by reading the device specs?
These Android devices should support the Android USB host API (i.e. Android 3.1 or higher) and should support full USB host.
Hopefully, there will be no more incomplete USB host implementation like the USB host feature of the Galaxy S2.
(((((
