The setting of parameters of the emulated KISS TNC is done in the
same way in the SCC driver. You can change parameters by using
the kissparms program from the ax25-utils package or use the program
“sccparam”:

sccparam <device> <paramname> <decimal-|hexadecimal value>

You can change the following parameters:

The parameters have the following meaning:

speed:

The baudrate on this channel in bits/sec

Example: sccparam /dev/scc3 speed 9600

txdelay:

The delay (in units of 10 ms) after keying of the
transmitter, until the first byte is sent. This is usually
called “TXDELAY” in a TNC. When 0 is specified, the driver
will just wait until the CTS signal is asserted. This
assumes the presence of a timer or other circuitry in the
MODEM and/or transmitter, that asserts CTS when the
transmitter is ready for data.
A normal value of this parameter is 30-36.

Example: sccparam /dev/scc0 txd 20

persist:

This is the probability that the transmitter will be keyed
when the channel is found to be free. It is a value from 0
to 255, and the probability is (value+1)/256. The value
should be somewhere near 50-60, and should be lowered when
the channel is used more heavily.

Example: sccparam /dev/scc2 persist 20

slottime:

This is the time between samples of the channel. It is
expressed in units of 10 ms. About 200-300 ms (value 20-30)
seems to be a good value.

Example: sccparam /dev/scc0 slot 20

tail:

The time the transmitter will remain keyed after the last
byte of a packet has been transferred to the SCC. This is
necessary because the CRC and a flag still have to leave the
SCC before the transmitter is keyed down. The value depends
on the baudrate selected. A few character times should be
sufficient, e.g. 40ms at 1200 baud. (value 4)
The value of this parameter is in 10 ms units.

Example: sccparam /dev/scc2 4

full:

The full-duplex mode switch. This can be one of the following
values:

Example: sccparam /dev/scc0 fulldup off

wait:

The initial waittime before any transmit attempt, after the
frame has been queue for transmit. This is the length of
the first slot in CSMA mode. In full duplex modes it is
set to 0 for maximum performance.
The value of this parameter is in 10 ms units.

Example: sccparam /dev/scc1 wait 4

maxkey:

The maximal time the transmitter will be keyed to send
packets, in seconds. This can be useful on busy CSMA
channels, to avoid “getting a bad reputation” when you are
generating a lot of traffic. After the specified time has
elapsed, no new frame will be started. Instead, the trans-
mitter will be switched off for a specified time (parameter
min), and then the selected algorithm for keyup will be
started again.
The value 0 as well as “off” will disable this feature,
and allow infinite transmission time.

Example: sccparam /dev/scc0 maxk 20

min:

This is the time the transmitter will be switched off when
the maximum transmission time is exceeded.

Example: sccparam /dev/scc3 min 10

idle:

This parameter specifies the maximum idle time in full duplex
2 mode, in seconds. When no frames have been sent for this
time, the transmitter will be keyed down. A value of 0 is
has same result as the fullduplex mode 1. This parameter
can be disabled.

Example: sccparam /dev/scc2 idle off # transmit forever

maxdefer

This is the maximum time (in seconds) to wait for a free channel
to send. When this timer expires the transmitter will be keyed
IMMEDIATELY. If you love to get trouble with other users you
should set this to a very low value 😉

Example: sccparam /dev/scc0 maxdefer 240 # 2 minutes

txoff:

When this parameter has the value 0, the transmission of packets
is enable. Otherwise it is disabled.

Example: sccparam /dev/scc2 txoff on

group:

It is possible to build special radio equipment to use more than
one frequency on the same band, e.g. using several receivers and
only one transmitter that can be switched between frequencies.
Also, you can connect several radios that are active on the same
band. In these cases, it is not possible, or not a good idea, to
transmit on more than one frequency. The SCC driver provides a
method to lock transmitters on different interfaces, using the
“param <interface> group <x>” command. This will only work when
you are using CSMA mode (parameter full = 0).

The number <x> must be 0 if you want no group restrictions, and
can be computed as follows to create restricted groups:
<x> is the sum of some OCTAL numbers:

Examples:

When 2 interfaces use group 201, their transmitters will never be
keyed at the same time.

When 2 interfaces use group 101, the transmitters will only key
when both channels are clear at the same time. When group 301,
the transmitters will not be keyed at the same time.

Don’t forget to convert the octal numbers into decimal before
you set the parameter.

Example: (to be written)

softdcd:

use a software dcd instead of the real one... Useful for a very
slow squelch.

Example: sccparam /dev/scc0 soft on