add an (incomplete) text document describing module parameters available in Zaptel modules

git-svn-id: http://svn.digium.com/svn/zaptel/branches/1.4@3783 5390a7c7-147a-4af0-8ec9-7488f05a26cb

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+ === Parameters for Zaptel modules ===
+
+(Note: this list is woefully incomplete, but is a starting point and
+will be improved as time permits.)
+
+ --- VPMADT032 Parameters ---
+
+The wctdm24xxp and wcte12xp drivers support cards which can have an
+optional VPMADT032 hardware echo canceler module. If that module is
+present, the following module parameters are available for these
+drivers:
+
+vpmsupport - 0 or 1, defaults to 1
+
+	Enables or disables use of the VPM.
+
+vpmdtmfsupport - 0 or 1, defaults to 0
+
+	Enables or disables DTMF tone detection on the VPM
+	(currently defaults to 'disabled' due to performance issues
+	when this functionality is enabled).
+
+vpmnlptype - 0 through 4, defaults to 1
+
+	Selects the type of non-linear processor that should be
+	applied when echo is detected and removed by the VPM. There
+	are five choices:
+
+		0 - None (not recommended)
+		1 - Mute (mutes the echo)
+		2 - Random Noise (replaces the echo with random noise)
+		3 - Hoth Noise (replaces the echo with Hoth noise)
+		4 - Suppress (suppresses the echo to a specified level)
+
+vpmnlpthresh - 0 through 40, in decibels (dB), defaults to 24
+
+	Relative signal level of echo to transmitted audio at which
+	NLP will be used to remove echo.
+
+vpmnlpmaxsupp - 0 through 90, in decibels (dB), defaults to 0
+
+	When vpmnlptype is 'Suppress', this value indicates the
+	relative energy level decrease that should be applied to the
+	echo signal).