3.3. Compiling Zaptel
Figure 3-1 shows the layers of
interaction between Asterisk and the Linux kernel with respect to
hardware control. On the Asterisk side is the Zapata channel
module, chan_zap. Asterisk uses
this interface to communicate with the Linux kernel, where the
drivers for the hardware are loaded.
The Zaptel interface is a kernel loadable module
that presents an abstraction layer between the hardware drivers and
the Zapata module in Asterisk. It is this concept that allows the
device drivers to be modified without
any changes being made to the Asterisk source itself. The device
drivers are used to communicate with the hardware directly and to
pass the information between Zaptel and the hardware.
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While Asterisk itself compiles on a variety of
platforms, the Zaptel drivers are Linux-specificthey are written to
interface directly with the Linux kernel. There are no official
Zaptel drivers for other operating systems, although work has been
going on to write drivers for FreeBSD.
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We will discuss the Zaptel compile-time options
momentarily, in "The zconfig.h File." First, let's take a look at
compiling and installing the drivers. (The
configuration of Zaptel drivers will be discussed in the next
chapter.)
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Before compiling
the Zaptel drivers on a system running a Linux 2.4 kernel , you should verify that /usr/src/ contains a symbolic link named
linux-2.4 pointing to your kernel
source. If the symbolic link doesn't exist, you can create it with
the following command (assuming you've installed the source in
/usr/src/):
# ln -s /usr/src/'uname -r' /usr/src/linux-2.4
Computers running Linux 2.6 kernel-based
distributions do not usually require the use of the symbolic link,
as these distributions will search for the kernel build directory
automatically. However, if you've placed the build directory in a
nonstandard place (i.e., somewhere other than /lib/modules/<kernel
version>/build/), you
will require the use of the symbolic link.
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3.3.1. The ztdummy Driver
In Asterisk, certain applications and features
require a timing device in order to operate (Asterisk won't even
compile them if no timing device is found). All Digium PCI hardware
provides a 1-kHz timing interface. If you lack the PCI hardware
required to provide timing, the ztdummy driver can be used as a timing device.
On Linux 2.4 kernel-based distributions, ztdummy must use the clocking provided by the
UHCI USB controller . The driver looks
to see that the usb-uhci module is
loaded and that the kernel version is at least 2.4.5. Older kernel
versions are incompatible with ztdummy.
On a 2.6 kernel-based distribution, ztdummy does not require the use of the USB
controller. (As of v2.6.0, the kernel now provides 1-kHz timing
with which the driver can interface; thus, the USB controller
hardware requirement is no longer necessary.)
The default Makefile configuration does not create
ztdummy. To compile ztdummy, you must remove a comment marker from
the Makefile. Open it in your
favorite text editor and look for the following line:
MODULES=zaptel tor2 torisa wcusb wcfxo wctdm \
ztdynamic ztd-eth wct1xxp wct4xxp wcte11xp # ztdummy
Remove the hash (#) symbol from in
front of "ztdummy," save the file, and compile Zaptel as usual.
3.3.2. The Zapata Telephony
Drivers
Compiling the Zapata telephony drivers for use
with your Digium hardware is straightforwardsimply run
make for either the 2.4 or 2.6 Linux kernels (the
Makefile will determine the kernel
version for you). Use these commands to compile Zaptel (replace
version with your version of zaptel):
# cd /usr/src/zaptel-version
# make clean
# make
# make install
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While running make clean is not always
necessary, it's a good idea to run it before recompiling any of the
modules, as it will remove the compiled binary files from within
the source code directory. You can also use it to clean up after
installing, if you don't like to leave the compiled binaries
floating around. Note that this removes the binaries only from the
source directory, not from the system.
In addition to the executables, make
clean also removes the intermediary files (i.e., the object
files) after compilation. You don't need them occupying space on
your hard drive.
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If you're using a system that makes use of the
/etc/rc.d/init.d/ or /etc/init.d/ directories, you may wish to run
the make config command as well. This will install the
startup scripts and configure the system, using the
chkconfig command to load the zaptel module automatically at startup.
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The Debian equivalent of chkconfig is
update-rc.d.
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3.3.3. Using ztcfg and zttool
Two programs installed along with Zaptel are
ztcfg and zttool. The ztcfg program is used to read the
configuration in /etc/zaptel.conf
to configure the hardware. The zttool program can be used to check the status
of your installed hardware. For instance, if you are using a T1
card and there is no communication between the endpoints, you will
see a red alarm. If everything is configured correctly and
communication is possible, you should see an "OK." The zttool application is also useful for analog
cards, because it tells you their current state (configured,
off-hook, etc.). The use of these programs will be explored further
in the next chapter.
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The libnewt
libraries and its development packages (newt-devel on Red Hat-based distributions)
must be installed for zttool to be
compiled.
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3.3.4. The zconfig.h File
The zconfig.h
file is where many of the Zaptel compile-time options lie. For the
most part, you should not need to edit this file, but below are
some of the options that may be of interest. To enable the options,
remove the comment tags (/* */). If you decide to enable
any of these options, be sure to do a make clean before
recompiling and reinstalling Zaptel.
3.3.4.1. Boost ringer
By enabling the BOOST_RINGER option,
you increase the amount of voltage supplied to a telephone during
ringing from ~70V to ~89V. Some devices may not detect ringing
below certain voltages, so this setting may be necessary. Note that
upping the voltage requires more power, and that it will probably
only be necessary on a telephone connected to a long loop.
Basically, you should leave this alone unless the far end isn't
detecting ringing properly. To enable this option, uncomment the
following line:
/* #define BOOST_RINGER */
The BOOST_RINGER option can also be
declared when loading the driver via modprobe, so it does
not need to be compiled into the driver (recommended).
3.3.4.2. Disable m-law/A-law precomputation
Defining CONFIG_CALC_XLAW tells Zaptel to not precompute m-law/A-law into tables and to recalculate it for
each sample. We haven't timed it, but the original coder felt that
if you have a small number of channels and/or a small level-2
cache, it may be quicker to execute the calculation code than to
actually do a lookup on the table loaded into memory.
To enable this option, uncomment the following
line within zconfig.h:
/* #define CONFIG_CALC_XLAW */
3.3.4.3. Enable MMX optimization
You can enable MMX optimization (if your
processor supports it) by removing the comment tags around the
following line:
/* #define CONFIG_ZAPTEL_MMX */
Be aware that CONFIG_ZAPTEL_MMX is
considered to be incompatible with AMD processors and can cause
system instability.
3.3.4.4. Choose echo cancellation
method
All the echo cancellers in Asterisk use a Finite
Impulse Response (FIR) algorithm. The differences between
themmostly in code implementation and slight algorithm tweaksare
minimal. By default, the MARK2
echo canceller is used, and it is generally considered the most
robust. To change the default, add comment tags around the
#define ECHO_CAN_MARK2 line and uncomment another
line:
/* #define ECHO_CAN_STEVE */
/* #define ECHO_CAN_STEVE2 */
/* #define ECHO_CAN_MARK */
#define ECHO_CAN_MARK2
/* #define ECHO_CAN_MARK3 */
3.3.4.5. Enable aggressive
suppression
Aggressive residual echo suppression with the
MARK2 echo canceller can be
enabled by removing the comment tags around the following line:
/* #define AGGRESSIVE_SUPPRESSOR */
The aggressive suppressor makes the nonlinear
processor (NLP) stronger. What the NLP essentially does is say, "If
the sample is that quiet anyway, make the volume level about
0."
3.3.4.6. Disable echo
cancellation
When echo cancellation is enabled in Asterisk,
it is possible to disable it by sending a 2100-Hz tone at the
beginning of a call. If you do not want Asterisk to disable echo
cancellation even when it detects the echo cancel disable tone,
uncomment the following line:
/* #define NO_ECHOCAN_DISABLE */
Fax machines and modems use the 2100-Hz tone
during negotiation , and Asterisk
monitors for this tone during call setup.
3.3.4.7. Enable HDLC
When using the Zaptel driver with T1 or E1
hardware, you can configure Zaptel to use TDM channels for data
instead of voice. To enable HDLC functionality in the drivers,
uncomment the following line:
/* #define CONFIG_ZAPATA_NET */
For this change to be meaningful, you must also
use the sethdlc utility and
perform some configuration in zapata.conf.
3.3.4.8. Enable ZapRAS
You can also make use of the ZapRAS program to turn Asterisk into a Remote
Access Server (RAS) for use with your ISDN connections. To enable
this functionality, you must uncomment the following line from
within the zconfig.h file:
/* #define CONFIG_ZAPATA_PPP */
You must also patch Asterisk and configure a PPP
daemon, so be aware that this task is nontrivial.
3.3.4.9. Enable Zaptel's watchdog
You can tell Zaptel to monitor the status of
interfaces via its built-in "watchdog." It will check if the
interfaces stop taking interrupts or otherwise misbehave. If this
happens, the hardware will automatically be restarted. To enable
the watchdog, uncomment this line:
/* #define CONFIG_ZAPTEL_WATCHDOG */
3.3.4.10. Set default tone zone
The tone zone info option is used to select
which set of tones (e.g., dial tone, busy indication, ring tone,
stutter, etc.), as defined in the zonedata.c file, should be used as the
default. The zonedata.c file
contains the frequencies and patterns that Asterisk uses to
communicate on the PSTN networks in various countries and to signal
connected telephones. The default tone zone (0) is used to indicate
North American signaling frequencies. Other tone zones include
Australia (1), France (2), Japan (7), Taiwan (14), and many others.
You can change the default on the following line:
#define DEFAULT_TONE_ZONE 0
3.3.4.11. Enable CAC ground start
signaling
Some devices, such as the FXO ports on a Carrier
Access Corporation (CAC) channel bank, have nonstandard FXS ground
start signaling start states (A=low, B=low). You can configure the
drivers to use this state by removing the comment tags around the
following line:
/* #define CONFIG_CAC_GROUNDSTART */
3.3.4.12. TDM400P Revision H PCI ID
workaround
If you happen to be using an older TDM400P
Revision H card, you may find that it sometimes forgets its PCI ID.
To make the wctdm driver
essentially match all subvendor IDs, uncomment the following
line:
/* #define TDM_REVH_MATCHALL */
This may be required when using older revisions
of TDM400P cards with newer versions of Asterisk, due to a change
in the subvendor ID code. This has been known to cause the
following type of error when loading the wctdm module:
# ZT_CHANCONFIG failed on channel 12: No such device or address (6)
Uncommenting the #define line above
should resolve this problem.
3.3.5. Passing Module Parameters to
Configure Zaptel
Some of the Zaptel options can also be enabled
when loading the module, by passing module parameters to the
wctdm driver. You can list these
parameters at load time (as opposed to statically changing them in
the zconfig.h file) with the
modinfo command:
# modinfo -p wctdm
debug int
loopcurrent int
robust int
_opermode int
opermode string
timingonly int
lowpower int
boostringer int
fxshonormode int
You then pass the module parameters to the
modprobe command. For example, you can use the following
command to activate the boostringer parameter when the
module is loaded, instead of statically defining its use with
#define BOOST_RINGER in the zconfig.h file:
# modprobe wctdm boostringer=1
Another common parameter to pass to a module is
opermode. By passing opermode to the wctdm driver, you can configure the TDM400P to
better deal with line impedances for your country.
opermode accepts a two-letter country code as its
argument.
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