1.. SPDX-License-Identifier: GPL-2.0
2
3===============================
4Linux Drivers for Baycom Modems
5===============================
6
7Thomas M. Sailer, HB9JNX/AE4WA, <sailer@ife.ee.ethz.ch>
8
9The drivers for the baycom modems have been split into
10separate drivers as they did not share any code, and the driver
11and device names have changed.
12
13This document describes the Linux Kernel Drivers for simple Baycom style
14amateur radio modems.
15
16The following drivers are available:
17====================================
18
19baycom_ser_fdx:
20  This driver supports the SER12 modems either full or half duplex.
21  Its baud rate may be changed via the ``baud`` module parameter,
22  therefore it supports just about every bit bang modem on a
23  serial port. Its devices are called bcsf0 through bcsf3.
24  This is the recommended driver for SER12 type modems,
25  however if you have a broken UART clone that does not have working
26  delta status bits, you may try baycom_ser_hdx.
27
28baycom_ser_hdx:
29  This is an alternative driver for SER12 type modems.
30  It only supports half duplex, and only 1200 baud. Its devices
31  are called bcsh0 through bcsh3. Use this driver only if baycom_ser_fdx
32  does not work with your UART.
33
34baycom_par:
35  This driver supports the par96 and picpar modems.
36  Its devices are called bcp0 through bcp3.
37
38baycom_epp:
39  This driver supports the EPP modem.
40  Its devices are called bce0 through bce3.
41  This driver is work-in-progress.
42
43The following modems are supported:
44
45======= ========================================================================
46ser12   This is a very simple 1200 baud AFSK modem. The modem consists only
47	of a modulator/demodulator chip, usually a TI TCM3105. The computer
48	is responsible for regenerating the receiver bit clock, as well as
49	for handling the HDLC protocol. The modem connects to a serial port,
50	hence the name. Since the serial port is not used as an async serial
51	port, the kernel driver for serial ports cannot be used, and this
52	driver only supports standard serial hardware (8250, 16450, 16550)
53
54par96   This is a modem for 9600 baud FSK compatible to the G3RUH standard.
55	The modem does all the filtering and regenerates the receiver clock.
56	Data is transferred from and to the PC via a shift register.
57	The shift register is filled with 16 bits and an interrupt is signalled.
58	The PC then empties the shift register in a burst. This modem connects
59	to the parallel port, hence the name. The modem leaves the
60	implementation of the HDLC protocol and the scrambler polynomial to
61	the PC.
62
63picpar  This is a redesign of the par96 modem by Henning Rech, DF9IC. The modem
64	is protocol compatible to par96, but uses only three low power ICs
65	and can therefore be fed from the parallel port and does not require
66	an additional power supply. Furthermore, it incorporates a carrier
67	detect circuitry.
68
69EPP     This is a high-speed modem adaptor that connects to an enhanced parallel
70	port.
71
72	Its target audience is users working over a high speed hub (76.8kbit/s).
73
74eppfpga This is a redesign of the EPP adaptor.
75======= ========================================================================
76
77All of the above modems only support half duplex communications. However,
78the driver supports the KISS (see below) fullduplex command. It then simply
79starts to send as soon as there's a packet to transmit and does not care
80about DCD, i.e. it starts to send even if there's someone else on the channel.
81This command is required by some implementations of the DAMA channel
82access protocol.
83
84
85The Interface of the drivers
86============================
87
88Unlike previous drivers, these drivers are no longer character devices,
89but they are now true kernel network interfaces. Installation is therefore
90simple. Once installed, four interfaces named bc{sf,sh,p,e}[0-3] are available.
91sethdlc from the ax25 utilities may be used to set driver states etc.
92Users of userland AX.25 stacks may use the net2kiss utility (also available
93in the ax25 utilities package) to convert packets of a network interface
94to a KISS stream on a pseudo tty. There's also a patch available from
95me for WAMPES which allows attaching a kernel network interface directly.
96
97
98Configuring the driver
99======================
100
101Every time a driver is inserted into the kernel, it has to know which
102modems it should access at which ports. This can be done with the setbaycom
103utility. If you are only using one modem, you can also configure the
104driver from the insmod command line (or by means of an option line in
105``/etc/modprobe.d/*.conf``).
106
107Examples::
108
109  modprobe baycom_ser_fdx mode="ser12*" iobase=0x3f8 irq=4
110  sethdlc -i bcsf0 -p mode "ser12*" io 0x3f8 irq 4
111
112Both lines configure the first port to drive a ser12 modem at the first
113serial port (COM1 under DOS). The * in the mode parameter instructs the driver
114to use the software DCD algorithm (see below)::
115
116  insmod baycom_par mode="picpar" iobase=0x378
117  sethdlc -i bcp0 -p mode "picpar" io 0x378
118
119Both lines configure the first port to drive a picpar modem at the
120first parallel port (LPT1 under DOS). (Note: picpar implies
121hardware DCD, par96 implies software DCD).
122
123The channel access parameters can be set with sethdlc -a or kissparms.
124Note that both utilities interpret the values slightly differently.
125
126
127Hardware DCD versus Software DCD
128================================
129
130To avoid collisions on the air, the driver must know when the channel is
131busy. This is the task of the DCD circuitry/software. The driver may either
132utilise a software DCD algorithm (options=1) or use a DCD signal from
133the hardware (options=0).
134
135======= =================================================================
136ser12   if software DCD is utilised, the radio's squelch should always be
137	open. It is highly recommended to use the software DCD algorithm,
138	as it is much faster than most hardware squelch circuitry. The
139	disadvantage is a slightly higher load on the system.
140
141par96   the software DCD algorithm for this type of modem is rather poor.
142	The modem simply does not provide enough information to implement
143	a reasonable DCD algorithm in software. Therefore, if your radio
144	feeds the DCD input of the PAR96 modem, the use of the hardware
145	DCD circuitry is recommended.
146
147picpar  the picpar modem features a builtin DCD hardware, which is highly
148	recommended.
149======= =================================================================
150
151
152
153Compatibility with the rest of the Linux kernel
154===============================================
155
156The serial driver and the baycom serial drivers compete
157for the same hardware resources. Of course only one driver can access a given
158interface at a time. The serial driver grabs all interfaces it can find at
159startup time. Therefore the baycom drivers subsequently won't be able to
160access a serial port. You might therefore find it necessary to release
161a port owned by the serial driver with 'setserial /dev/ttyS# uart none', where
162# is the number of the interface. The baycom drivers do not reserve any
163ports at startup, unless one is specified on the 'insmod' command line. Another
164method to solve the problem is to compile all drivers as modules and
165leave it to kmod to load the correct driver depending on the application.
166
167The parallel port drivers (baycom_par, baycom_epp) now use the parport subsystem
168to arbitrate the ports between different client drivers.
169
170vy 73s de
171
172Tom Sailer, sailer@ife.ee.ethz.ch
173
174hb9jnx @ hb9w.ampr.org
175