usrp-e100: added app notes for fpga loading and reclocking

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diff --git a/host/docs/usrp_e1xx.rst b/host/docs/usrp_e1xx.rst
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+========================================================================
+UHD - USRP-E1XX Series Application Notes
+========================================================================
+
+.. contents:: Table of Contents
+
+------------------------------------------------------------------------
+Specify a non-standard image
+------------------------------------------------------------------------
+The UHD will automatically select the USRP embedded FPGA image from the installed images package.
+The FPGA image selection can be overridden with the "fpga" device address parameter.
+
+Example device address string representations to specify non-standard FPGA image:
+
+::
+
+    fpga=usrp_e100_custom.bin
+
+------------------------------------------------------------------------
+Changing the master clock rate
+------------------------------------------------------------------------
+The master clock rate of the USRP embedded feeds both the FPGA DSP and the codec chip.
+UHD can dynamically reconfigure the clock rate though the set_master_clock_rate() API call.
+Hundreds of rates between 32MHz and 64MHz are available.
+A few notable rates are:
+
+* 64MHz - maximum rate of the codec chip
+* 61.44MHz - good for UMTS/WCDMA applications
+* 52Mhz - good for GSM applications
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Set 61.44MHz - uses external VCXO
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+To use the 61.44MHz clock rate, the USRP embedded will require two jumpers to be moved.
+
+* J16 is a two pin header, remove the jumper (or leave it on pin1 only)
+* J15 is a three pin header, move the jumper to (pin1, pin2)
+
+For the correct clock settings, call usrp->set_master_clock_rate(61.44e6)
+before any other parameters are set in your application.
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Set other rates - uses internal VCO
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+To use other clock rates, the jumpers will need to be in the default position.
+
+* J16 is a two pin header, move the jumper to (pin1, pin2)
+* J15 is a three pin header, move the jumper to (pin2, pin3)
+
+For the correct clock settings, call usrp->set_master_clock_rate(rate)
+before any other parameters are set in your application.