DSD demod: updated readme with information on DV serial device support

plugins/channel/demoddsd/readme.md

@@ -9,16 +9,27 @@ This plugin uses the [DSDcc](https://github.com/f4exb/dsdcc) library that has be
 
 The modulation and format is automatically detected and switched.
 
-DSDcc itself uses [mbelib](https://github.com/szechyjs/mbelib) to decode AMBE frames. While DSDcc is intended to be patent-free, `mbelib` that it uses describes functions that may be covered by one or more U.S. patents owned by DVSI Inc. The source code itself should not be infringing as it merely describes possible methods of implementation. Compiling or using `mbelib` may infringe on patents rights in your jurisdiction and/or require licensing. It is unknown if DVSI will sell licenses for software that uses `mbelib`.
+To enable this plugin at compile time you will need to have DSDcc installed in your system. Please follow instructions in [DSDcc readme](https://github.com/f4exb/dsdcc/blob/master/Readme.md) to build and install DSDcc. If you install it in a custom location say `/opt/install/dsdcc` you will need to add these defines to the cmake command: `-DLIBDSDCC_INCLUDE_DIR=/opt/install/dsdcc/include/dsdcc -DLIBDSDCC_LIBRARIES=/opt/install/dsdcc/lib/libdsdcc.so`
+
+<h2>DV serial device support</h2>
+
+You can use a serial device connected to your system that implements and exposes the packet interface of the AMBE3000 chip. This can be for example a ThumbDV USB dongle. In order to support DV serial devices in your system you will need two things:
+
+  - Compile with [SerialDV](https://github.com/f4exb/serialDV) support Please refer to this project Readme.md to compile and install SerialDV. If you install it in a custom location say `/opt/install/serialdv` you will need to add these defines to the cmake command: `-DLIBSERIALDV_INCLUDE_DIR=/opt/install/serialdv/include/serialdv -DLIBSERIALDV_LIBRARY=/opt/install/serialdv/lib/libserialdv.so`
+  - Enable DV serial devices in your system by checking the option in the Preferences menu. YOu will need to enable the DV serial devices each time you start SDRangel.
+  
+Please note that such serial devices work with a serial interface at 400 kb. While this seems large for a serial interface this limits the throughput and hence the capability of decoding several channels in parallel. The software can enqueue requests over many devices so the more you have the more channels you can decode in parallel. Note also that a channel that does not output voice frames will not require a device for decoding so only channels that receive voice frames at any one time will require a DV serial device.
+
+<h2>Mbelib support</h2>
+
+DSDcc itself can use [mbelib](https://github.com/szechyjs/mbelib) to decode AMBE frames. While DSDcc is intended to be patent-free, `mbelib` that it uses describes functions that may be covered by one or more U.S. patents owned by DVSI Inc. The source code itself should not be infringing as it merely describes possible methods of implementation. Compiling or using `mbelib` may infringe on patents rights in your jurisdiction and/or require licensing. It is unknown if DVSI will sell licenses for software that uses `mbelib`.
 
 If you are not comfortable with this just do not install DSDcc and/or mbelib and the plugin will not be compiled and added to SDRangel. For packaged distributions just remove:
 
   - For Linux distributions: `plugins/channel/libdemoddsd.so`
   - For Windows distributions: `dsdcc.dll`, `mbelib.dll`, `plugins\channel\demoddsd.dll`
 
-If you choose to compile and install this plugin you will need to have DSDcc installed in your system. Please follow instructions in [DSDcc readme](https://github.com/f4exb/dsdcc/blob/master/Readme.md) to build and install DSDcc. If you install it in a custom location say `/opt/install/dsdcc` you will need to add these defines to the cmake command: `-DLIBDSDCC_INCLUDE_DIR=/opt/install/dsdcc/include/dsdcc -DLIBDSDCC_LIBRARIES=/opt/install/dsdcc/lib/libdsdcc.so`
-
-If you have mbelib installed in a custom location, say `/opt/install/mbelib` you will need to add these defines to the cmake command: `-DLIBMBE_INCLUDE_DIR=/opt/install/mbelib/include -DLIBMBE_LIBRARY=/opt/install/mbelib/lib/libmbe.so`
+For software built fron source if you choose to have `mbelib` support you will need to have DSDcc compiled with `mbelib` support. You will also need to have defines for it on the cmake command. If you have mbelib installed in a custom location, say `/opt/install/mbelib` you will need to add these defines to the cmake command: `-DLIBMBE_INCLUDE_DIR=/opt/install/mbelib/include -DLIBMBE_LIBRARY=/opt/install/mbelib/lib/libmbe.so`
 
 <h2>Interface</h2>