README, UPGRADE.txt, system.conf.sample: Add documentation for using HWEC

Update documentation to the effect that HWEC is not enabled by default
and must be enabled manually if desired via "echocanceller" in system.conf.


git-svn-id: http://svn.astersk.org/svn/dahdi/tools/trunk@9528 17933a7a-c749-41c5-a318-cba88f637d49

README

@@ -106,7 +106,9 @@ channels, and send it to the kernel.
 A sample annotated system.conf is included in this directory and
 installed by default. Edit it to suit your configuration. Alternatively 
 use the script dahdi_genconf to generate one that should work with your 
-system.
+system. Note that while dahdi_genconf will generate a working configuration,
+it will not automatically detect hardware echo cancellation modules.  These
+will have to be enabled manually in system.conf.
 
 /etc/dahdi/init.conf
 ~~~~~~~~~~~~~~~~~~~~

UPGRADE.txt

@@ -62,10 +62,9 @@ Any or all of these modules can be loaded at the same time, and the echo
 canceler to be used on the system's channels can be configured using
 the dahdi_cfg tool from the dahdi-tools package.
 
-IMPORTANT: It is *mandatory* to configure an echo canceler for the
-system's channels using dahdi_cfg unless the interface cards in use
-have echo canceler modules available and enabled. There is *no*
-default software echo canceler with DAHDI. See
+IMPORTANT: It is *mandatory* to configure an echo canceler for the system's
+channels using dahdi_cfg. There is *no* default echo canceler with DAHDI, not
+even hardware echo cancellation modules. See
 <<_echo_cancellers,section on echo cancellers>> in sample system.conf.
 
 

system.conf.sample

@@ -312,10 +312,11 @@ defaultzone=us
 # cancellers are compiled and installed as part of the dahdi-linux package.
 # You can specify in this file the echo canceller to be used for each
 # channel. The default behavior is for there to be NO echo canceller on any
-# channel, so it is very important that you specify one here if you do
-# not have hardware echo cancellers and need echo cancellation.
+# channel, so it is very important that you specify one here.
 #
-# Valid echo cancellers are: mg2, kb1, sec2, and sec.
+# Valid echo cancellers are: hwec, mg2, kb1, sec2, and sec.
+# 'hwec' is a special echo canceller that should be used if hardware echo
+# cancellation is desired on and available on the specified channels.
 # If compiled, 'hpec' is also a valid echo canceller.
 # 
 # To configure the default echo cancellers, use the format: