175 lines
7.2 KiB
ReStructuredText
175 lines
7.2 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
===============================
|
|
Linux Drivers for Baycom Modems
|
|
===============================
|
|
|
|
Thomas M. Sailer, HB9JNX/AE4WA, <sailer@ife.ee.ethz.ch>
|
|
|
|
The drivers for the baycom modems have been split into
|
|
separate drivers as they did not share any code, and the driver
|
|
and device names have changed.
|
|
|
|
This document describes the Linux Kernel Drivers for simple Baycom style
|
|
amateur radio modems.
|
|
|
|
The following drivers are available:
|
|
====================================
|
|
|
|
baycom_ser_fdx:
|
|
This driver supports the SER12 modems either full or half duplex.
|
|
Its baud rate may be changed via the ``baud`` module parameter,
|
|
therefore it supports just about every bit bang modem on a
|
|
serial port. Its devices are called bcsf0 through bcsf3.
|
|
This is the recommended driver for SER12 type modems,
|
|
however if you have a broken UART clone that does not have working
|
|
delta status bits, you may try baycom_ser_hdx.
|
|
|
|
baycom_ser_hdx:
|
|
This is an alternative driver for SER12 type modems.
|
|
It only supports half duplex, and only 1200 baud. Its devices
|
|
are called bcsh0 through bcsh3. Use this driver only if baycom_ser_fdx
|
|
does not work with your UART.
|
|
|
|
baycom_par:
|
|
This driver supports the par96 and picpar modems.
|
|
Its devices are called bcp0 through bcp3.
|
|
|
|
baycom_epp:
|
|
This driver supports the EPP modem.
|
|
Its devices are called bce0 through bce3.
|
|
This driver is work-in-progress.
|
|
|
|
The following modems are supported:
|
|
|
|
======= ========================================================================
|
|
ser12 This is a very simple 1200 baud AFSK modem. The modem consists only
|
|
of a modulator/demodulator chip, usually a TI TCM3105. The computer
|
|
is responsible for regenerating the receiver bit clock, as well as
|
|
for handling the HDLC protocol. The modem connects to a serial port,
|
|
hence the name. Since the serial port is not used as an async serial
|
|
port, the kernel driver for serial ports cannot be used, and this
|
|
driver only supports standard serial hardware (8250, 16450, 16550)
|
|
|
|
par96 This is a modem for 9600 baud FSK compatible to the G3RUH standard.
|
|
The modem does all the filtering and regenerates the receiver clock.
|
|
Data is transferred from and to the PC via a shift register.
|
|
The shift register is filled with 16 bits and an interrupt is signalled.
|
|
The PC then empties the shift register in a burst. This modem connects
|
|
to the parallel port, hence the name. The modem leaves the
|
|
implementation of the HDLC protocol and the scrambler polynomial to
|
|
the PC.
|
|
|
|
picpar This is a redesign of the par96 modem by Henning Rech, DF9IC. The modem
|
|
is protocol compatible to par96, but uses only three low power ICs
|
|
and can therefore be fed from the parallel port and does not require
|
|
an additional power supply. Furthermore, it incorporates a carrier
|
|
detect circuitry.
|
|
|
|
EPP This is a high-speed modem adaptor that connects to an enhanced parallel
|
|
port.
|
|
|
|
Its target audience is users working over a high speed hub (76.8kbit/s).
|
|
|
|
eppfpga This is a redesign of the EPP adaptor.
|
|
======= ========================================================================
|
|
|
|
All of the above modems only support half duplex communications. However,
|
|
the driver supports the KISS (see below) fullduplex command. It then simply
|
|
starts to send as soon as there's a packet to transmit and does not care
|
|
about DCD, i.e. it starts to send even if there's someone else on the channel.
|
|
This command is required by some implementations of the DAMA channel
|
|
access protocol.
|
|
|
|
|
|
The Interface of the drivers
|
|
============================
|
|
|
|
Unlike previous drivers, these drivers are no longer character devices,
|
|
but they are now true kernel network interfaces. Installation is therefore
|
|
simple. Once installed, four interfaces named bc{sf,sh,p,e}[0-3] are available.
|
|
sethdlc from the ax25 utilities may be used to set driver states etc.
|
|
Users of userland AX.25 stacks may use the net2kiss utility (also available
|
|
in the ax25 utilities package) to convert packets of a network interface
|
|
to a KISS stream on a pseudo tty. There's also a patch available from
|
|
me for WAMPES which allows attaching a kernel network interface directly.
|
|
|
|
|
|
Configuring the driver
|
|
======================
|
|
|
|
Every time a driver is inserted into the kernel, it has to know which
|
|
modems it should access at which ports. This can be done with the setbaycom
|
|
utility. If you are only using one modem, you can also configure the
|
|
driver from the insmod command line (or by means of an option line in
|
|
``/etc/modprobe.d/*.conf``).
|
|
|
|
Examples::
|
|
|
|
modprobe baycom_ser_fdx mode="ser12*" iobase=0x3f8 irq=4
|
|
sethdlc -i bcsf0 -p mode "ser12*" io 0x3f8 irq 4
|
|
|
|
Both lines configure the first port to drive a ser12 modem at the first
|
|
serial port (COM1 under DOS). The * in the mode parameter instructs the driver
|
|
to use the software DCD algorithm (see below)::
|
|
|
|
insmod baycom_par mode="picpar" iobase=0x378
|
|
sethdlc -i bcp0 -p mode "picpar" io 0x378
|
|
|
|
Both lines configure the first port to drive a picpar modem at the
|
|
first parallel port (LPT1 under DOS). (Note: picpar implies
|
|
hardware DCD, par96 implies software DCD).
|
|
|
|
The channel access parameters can be set with sethdlc -a or kissparms.
|
|
Note that both utilities interpret the values slightly differently.
|
|
|
|
|
|
Hardware DCD versus Software DCD
|
|
================================
|
|
|
|
To avoid collisions on the air, the driver must know when the channel is
|
|
busy. This is the task of the DCD circuitry/software. The driver may either
|
|
utilise a software DCD algorithm (options=1) or use a DCD signal from
|
|
the hardware (options=0).
|
|
|
|
======= =================================================================
|
|
ser12 if software DCD is utilised, the radio's squelch should always be
|
|
open. It is highly recommended to use the software DCD algorithm,
|
|
as it is much faster than most hardware squelch circuitry. The
|
|
disadvantage is a slightly higher load on the system.
|
|
|
|
par96 the software DCD algorithm for this type of modem is rather poor.
|
|
The modem simply does not provide enough information to implement
|
|
a reasonable DCD algorithm in software. Therefore, if your radio
|
|
feeds the DCD input of the PAR96 modem, the use of the hardware
|
|
DCD circuitry is recommended.
|
|
|
|
picpar the picpar modem features a builtin DCD hardware, which is highly
|
|
recommended.
|
|
======= =================================================================
|
|
|
|
|
|
|
|
Compatibility with the rest of the Linux kernel
|
|
===============================================
|
|
|
|
The serial driver and the baycom serial drivers compete
|
|
for the same hardware resources. Of course only one driver can access a given
|
|
interface at a time. The serial driver grabs all interfaces it can find at
|
|
startup time. Therefore the baycom drivers subsequently won't be able to
|
|
access a serial port. You might therefore find it necessary to release
|
|
a port owned by the serial driver with 'setserial /dev/ttyS# uart none', where
|
|
# is the number of the interface. The baycom drivers do not reserve any
|
|
ports at startup, unless one is specified on the 'insmod' command line. Another
|
|
method to solve the problem is to compile all drivers as modules and
|
|
leave it to kmod to load the correct driver depending on the application.
|
|
|
|
The parallel port drivers (baycom_par, baycom_epp) now use the parport subsystem
|
|
to arbitrate the ports between different client drivers.
|
|
|
|
vy 73s de
|
|
|
|
Tom Sailer, sailer@ife.ee.ethz.ch
|
|
|
|
hb9jnx @ hb9w.ampr.org
|