28.3 Infrared Data Transmission
IrDA (Infrared Data Association) is an industry standard
for wireless communication with infrared light. Many laptops sold today are
equipped with an IrDA-compatible transceiver that enables communication with
other devices, such as printers, modems, LANs, or other laptops. The transfer
speed ranges from 2400 bps to 4 Mbps.
There are two IrDA operation modes. The standard mode, SIR, accesses the
infrared port through a serial interface. This mode works on almost all
systems and is sufficient for most requirements. The faster mode, FIR,
requires a special driver for the IrDA chip. Not all chip types are supported
in FIR mode because of a lack of appropriate drivers. Set the desired IrDA
mode in the BIOS of your computer. The BIOS also shows which
serial interface is used in SIR mode.
Find information about IrDA in the IrDA how-to by Werner Heuser at
https://tuxmobil.org/Infrared-HOWTO/Infrared-HOWTO.html.
Additionally refer to the Web site of the Linux IrDA Project at https://irda.sourceforge.net/.
28.3.1 Software
The necessary kernel modules are included in the kernel package. The package
irda provides the necessary helper
applications for supporting the infrared interface. Find the documentation
at /usr/share/doc/packages/irda/README after the
installation of the package.
28.3.2 Configuration
The IrDA system service is not started automatically when the system is
booted. Use the YaST IrDA module for activation. Only one setting can
be modified in this module: the serial interface of the infrared device. The
test window shows two outputs. One is the output of
irdadump, which logs all sent and received IrDA packets.
This output should contain the name of the computer and the names of all
infrared devices in transmission range. An example for these messages is
shown in Section 28.3.4,
Troubleshooting. All
devices to which an IrDA connection exists are listed in the lower part of
the window.
IrDA consumes a considerable amount of battery power, because a discovery
packet is sent every few seconds to detect other
peripheral devices. Therefore, IrDA should only be started when
necessary if you depend on battery power. Enter the command
rcirda start to activate
it or rcirda stop to
deactivate it. All needed kernel modules
are loaded automatically when the
interface is activated.
If preferred, configure manually in the file
/etc/sysconfig/irda. This file contains
only one variable, IRDA_PORT, which determines
the interface to use in SIR mode.
28.3.3 Usage
Data can be sent to the device file /dev/irlpt0
for printing. The device file /dev/irlpt0 acts just
like the normal /dev/lp0 cabled interface, except the
printing data is sent wirelessly with infrared light.
For printing, make sure that the printer is in visual
range of the computer's infrared interface
and the infrared support is started.
A printer that is operated over the infrared interface can be configured
with the YaST printer module. Because it is not detected automatically,
configure it manually by clicking
. Select and click
to configure the printer device. Usually,
irlpt0 is the right connection. Click
to apply your settings. Details about operating
printers in Linux are available in Section 19.0,
Printer Operation.
Communication with other hosts and with mobile phones or other similar
devices is conducted through the device file
/dev/ircomm0. The Siemens S25 and Nokia 6210
mobile phones, for example, can dial and connect to the Internet with the
wvdial application using the infrared interface.
Synchronizing data with a Palm Pilot is also possible, provided the
device setting of the corresponding application has been set to
/dev/ircomm0.
If you want, you can address only devices that support the printer or IrCOMM
protocols. Devices that support the IROBEX protocol, such as the 3Com Palm
Pilot, can be accessed with special applications, like irobexpalm and
irobexreceive. Refer to the IR-HOWTO (https://tldp.org/HOWTO/Infrared-HOWTO/) for information. The
protocols supported by the device are listed in brackets after the name of
the device in the output of irdadump. IrLAN protocol
support is still a work in progress.
28.3.4 Troubleshooting
If devices connected to the infrared port do not respond, use the command
irdadump (as root) to
check if the other device is recognized by the computer. Something similar
to Example 28-1 appears regularly when a Canon BJC-80 printer
is in visible range of the computer:
Example 28-1
Output of irdadump
21:41:38.435239 xid:cmd 5b62bed5 > ffffffff S=6 s=0 (14)
21:41:38.525167 xid:cmd 5b62bed5 > ffffffff S=6 s=1 (14)
21:41:38.615159 xid:cmd 5b62bed5 > ffffffff S=6 s=2 (14)
21:41:38.705178 xid:cmd 5b62bed5 > ffffffff S=6 s=3 (14)
21:41:38.795198 xid:cmd 5b62bed5 > ffffffff S=6 s=4 (14)
21:41:38.885163 xid:cmd 5b62bed5 > ffffffff S=6 s=5 (14)
21:41:38.965133 xid:rsp 5b62bed5 < 6cac38dc S=6 s=5 BJC-80
hint=8804 [Printer IrCOMM ] (23)
21:41:38.975176 xid:cmd 5b62bed5 > ffffffff S=6 s=* earth
hint=0500 [ PnP Computer ] (21)
Check the configuration of the interface if there is no output or
the other device does not reply. Verify that the correct interface is used.
The infrared interface is sometimes located at
/dev/ttyS2 or at /dev/ttyS3 and
an interrupt other than IRQ 3 is sometimes used. These settings can be
checked and modified in the BIOS setup menu of almost every laptop.
A simple video camera can also help in determining whether the
infrared LED lights up at all. Most video cameras can see infrared light;
the human eye cannot.
