sethdlc - get/set Linux HDLC packet radio modem driver port information
sethdlc [ -bdhs ] [-i device]
sethdlc [-i device] -c cal
sethdlc -p [-i device] [ mode mode ] [ io iobase ] [ irq irq ]
[ dma dma ] [ dma2 dma2 ] [ serio seriobase ] [ pario pariobase ]
[ midiio midiiobase ] [ options options ]
sethdlc -a [-i device] [ txd txdelay ] [ txtail txtail ]
[ slot slottime ] [ ppersist ppersistence ] [ full ] [ half ]
sethdlc is a program designed to set and/or report the configuration
information associated with a soundcard radio modem port. This
information includes the modem type, what I/O port, IRQ and DMA channel
a particular modem port is using, and where to output a transmitter
keying (PTT) signal.
With the -p option, sethdlc sets and/or reports the port configuration.
With the -a option, sethdlc sets and/or reports the AX.25 channel
access parameters. These parameters can also be set with the kissparms
With the -c option, sethdlc instructs the driver to send a calibration
pattern for cal seconds.
Without the -p, -a and -c option, sethdlc will stay in the foreground
and display received packets. The AX.25 header and eventually a FlexNet
compressed header are decoded. CTRL-C terminates sethdlc. Specifying
additional options, sethdlc may display additional information.
sethdlc accepts the following options:
-b Trace the bits at the output of the demodulator, after RX clock
recovery. This option is only available if sethdlc and the
soundcard modem kernel driver is compiled with debugging support
on. This is useful for driver debugging.
-d Trace DCD, PTT and other status information on stdout. sethdlc
displays two times per second a line containing these
-h Display an overview of the available command line parameters and
-i The device argument specifies the HDLC modem device which should
be configured or interrogated. It will usually have the
following form: bc[0-3] for the baycom driver and sm[0-3] for
the soundcard modem driver.
-s Trace the bits at the demodulator output, before the RX clock
recovery, to stdout. This option is only available the modem
driver is compiled with debugging support on. It may not be
available on some modem, such as the par96.
The following parameters can be assigned to a soundcard radio modem
All numerical parameter values are assumed to be in decimal unless
preceeded by "0x".
The mode parameter sets the type of hardware and the operating mode of
the driver. ser12 and par96 are valid modes for the baycom driver. A
star "*" may be added to enable software DCD. The mode string format of
the soundmodem driver is as follows: hw:mode. hw may be either sbc,
wss or wssfdx. The first one specifies SoundBlaster compatible
soundcards, the second one WindowsSoundSystem compatible hardware, and
the third one WSS fullduplex operation (which currently works with
Crystal Semiconductor Chipsets CS423). The mode portion may be
afsk1200 or fsk9600. Optionally, the receive and transmit modes may be
The ioport parameter sets the I/O port address. Typical values for the
ser12 modem are 0x3f8, 0x2f8, 0x3e8 or 0x2e8, for the par96 modem
0x378, 0x278 or 0x3bc, for the sbc modems 0x220 and for the wss modems
0x530, 0x608, 0xe80 or 0xf40.
The irq parameter sets the hardware IRQ number. Typical values for the
ser12 modem are 4 and 3, for the par96 modem 7 or 5, for the sbc modems
are 7 or 5 and for the wss modems, any free IRQ from the set 2, 7, 9,
10, 11 will do. The driver automatically configures the WSS soundcard
to the correct IRQ.
The dma parameter sets the hardware DMA number. Typical values for the
sbc modems are 1 or 0 and for the wss modems, any free DMA from 0 to 3
(except 2) will do. The driver automatically configures the WSS
soundcard to the correct DMA. The Baycom modems do not need DMA.
The dma2 parameter sets the second hardware DMA number. This is only
needed for full duplex operation with the soundmodem driver.
The seriobase parameter optionally sets the address of a serial port,
where the driver will output a PTT signal at the TxD and RTS pins, and
a DCD signal at the DTR pin. As Baycom modems do have their own PTT
pin, this parameter is not used by the Baycom modem driver.
The pariobase parameter optionally sets the address of a LPT port where
the driver will output a PTT signal on the DATA0 line and a DCD signal
on the DATA1 line. As Baycom modems do have their own PTT pin, this
parameter is not used by the Baycom modem driver.
The midiiobase parameter optionally sets the address of a MPU401
compatible MIDI port, where the driver will output a PTT signal. Since
the MIDI port is effectively an UART and therefore cannot output a DC
signal, the output must be fed through a retriggerable monoflop with a
period of about 15ms. See
http://www.ife.ee.ethz.ch/~sailer/pcf/ptt_circ/ptt.html for a sample
schematic diagram. As Baycom modems do have their own PTT pin, this
parameter is not used by the Baycom modem driver.
The txdelay sets the transmitter keyup delay time. Unlike kissparms,
the unit is tens of ms. This is the time the transmitter needs to
switch its PA on and for its frequency synthesizer to settle. Typical
values for a handheld transceiver are 200ms (i.e. 20), and for a good
crystal driven transceiver 20ms (i.e. 2).
The txtail sets the time PTT is held after the last packet. Unlike
kissparms, the unit is tens of ms. Do not set this value to 0. Most
modems need some extra time to actually clock the last bits out to the
The slottime parameter specifies how often the channel access algorithm
is executed. Unlike kissparms, the unit is tens of ms. Unless you have
very specific requirements, set this to 100ms (i.e. 10).
The ppersist sets how "eagerly" the station starts to transmit as soon
as the channel gets free. The optimum value is 256 divided by the
number of stations on the channel. (This should really be done
automatically by the L2)
full sets the modem to full duplex mode. Note that some modems do not
actually support full duplex mode, in this case this parameter makes
the modem start its transmission as soon as it gets packets from the
upper layer, without waiting for the channel to become free. This is
needed by some implementations of alternative channel access
algorithms, e.g. DAMA.
half sets the modem to half duplex mode.
CONSIDERATIONS OF CONFIGURING BAYCOM PORTS
It is important to note that sethdlc merely tells the Linux kernel
where it should expect to find the I/O port and IRQ lines of a
particular serial port. It does not configure the hardware to use a
particular I/O port. In order to do that, you will need to physically
program the serial board, usually by setting some jumpers or by
switching some DIP switches.
This section will provide some pointers in helping you decide how you
would like to configure your baycom ports.
The "standard MS-DOS" port associations are given below:
COM1, port 0x3f8, irq 4
COM2, port 0x2f8, irq 3
COM3, port 0x3e8, irq 4
COM4, port 0x2e8, irq 3
LPT1, port 0x378, irq 7
LPT1 (on hercules graphics adapter), port 0x3bc, irq 7
LPT1, port 0x278, irq 5
CONSIDERATIONS OF CONFIGURING SOUNDCARD RADIO MODEM PORTS
Some cards need to be initialized before they act as a WSS or
SoundBlaster compatible card. This driver does not do this. You can use
the standard linux sound driver, if compiled as a module. Just load the
sound driver (insmod sound) and remove it again (rmmod sound). The card
should then be configured for either soundblaster or WSS compatibility.
If this does not work for some reason, you’ll have to write your own
soundcard configuration utility. This is not as complicated as it
sounds; it can be done from user space (but requiring root privileges)
using ioperm and/or iopl.
It is important that the audio levels of your radio match those of the
soundcard. To help achieve this, there are two utilities: smdiag and
smmixer. See their respective manpage.
The sound driver and the soundcard modem driver are mutually exclusive,
i.e. they cannot both access the same soundcard at the same time. Even
worse, the sound driver reserves the soundcard as soon as it gets
loaded. The souncard modem driver however reserves the card only when
the interface is started, i.e. during ifconfig sm[0-3] up.
9600 baud may not currently work on SoundBlaster cards with DSP
revision 4.x, i.e. SB16 and SB32 AWE. This is because they seem to not
be fully backwards compatible.
CAUTION: Using an invalid port can lock up your machine.
smdiag (8), smmixer (8), kissparms (8),
sethdlc was written by Thomas Sailer, HB9JNX/AE4WA
(firstname.lastname@example.org). Inspired by setserial.