User guide

106 RealCT Direct API Developer Guide
Chapter 4: E1 Networking
Configuring Debounce
When debouncing is enabled, the board waits for the signaling
bits to be stable before relaying the information to the devices.
Waiting for the bits to stabilize prevents errors from being
handled as if they were valid signals. Debouncing, which is also
called deglitching, should always be enabled.
The ‘6’ to ‘9’ msec wait is less than the minimum time used for
signal recognition protocols, so enabling debouncing should not
impact performance. In fact, it should increase performance,
despite the delay, since the software does not have to handle
spurious signals. The software adds an additional debouncing
time at a higher layer, which further reduces the risk of
spurious signals reaching the application.
Configuring the Loopback Mode
There are two software loopbacks set using
CONFIG_CARRIER: remote and local. These are used to test a
board or the data link. For information about additional
hardware loopbacks, see Troubleshooting on page 134.
In a remote loopback, the board immediately transmits all
data it receives back to the CO. If all connections are
working, the CO should receive the same information it
transmitted. If any transmission errors disappear in the
remote loopback configuration, the problem is with the
clock or carrier settings in your application. If the problem
does not disappear, the problem is either the cabling or at
the carrier end.
In a local loopback, the board receives the same data it
transmits, without passing through any cabling. If placing
your board in a local loopback fixes problems you
experienced on the line, the problem is with the cabling or
with the carrier. If a local loopback does not fix errors, then
the board is not sending valid data.
When you first load the driver, it has both loopback modes
enabled by default. In this configuration, both the board and the
CO only receive the data they transmit. This configuration lets
you verify that both the board and CO can send and receive
valid data. For normal operation, remove both loopbacks so that
the board and CO can transmit and receive data.