1 .. SPDX-License-Identifier: GPL-2.0
2
3 ===============================
4 Linux Drivers for Baycom Modems
5 ===============================
6
7 Thomas M. Sailer, HB9JNX/AE4WA, <sailer@ife.ee.ethz.ch>
8
9 The drivers for the baycom modems have been split into
10 separate drivers as they did not share any code, and the driver
11 and device names have changed.
12
13 This document describes the Linux Kernel Drivers for simple Baycom style
14 amateur radio modems.
15
16 The following drivers are available:
17 ====================================
18
19 baycom_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
28 baycom_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
34 baycom_par:
35 This driver supports the par96 and picpar modems.
36 Its devices are called bcp0 through bcp3.
37
38 baycom_epp:
39 This driver supports the EPP modem.
40 Its devices are called bce0 through bce3.
41 This driver is work-in-progress.
42
43 The following modems are supported:
44
45 ======= ========================================================================
46 ser12 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
54 par96 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
63 picpar 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
69 EPP 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
74 eppfpga This is a redesign of the EPP adaptor.
75 ======= ========================================================================
76
77 All of the above modems only support half duplex communications. However,
78 the driver supports the KISS (see below) fullduplex command. It then simply
79 starts to send as soon as there's a packet to transmit and does not care
80 about DCD, i.e. it starts to send even if there's someone else on the channel.
81 This command is required by some implementations of the DAMA channel
82 access protocol.
83
84
85 The Interface of the drivers
86 ============================
87
88 Unlike previous drivers, these drivers are no longer character devices,
89 but they are now true kernel network interfaces. Installation is therefore
90 simple. Once installed, four interfaces named bc{sf,sh,p,e}[0-3] are available.
91 sethdlc from the ax25 utilities may be used to set driver states etc.
92 Users of userland AX.25 stacks may use the net2kiss utility (also available
93 in the ax25 utilities package) to convert packets of a network interface
94 to a KISS stream on a pseudo tty. There's also a patch available from
95 me for WAMPES which allows attaching a kernel network interface directly.
96
97
98 Configuring the driver
99 ======================
100
101 Every time a driver is inserted into the kernel, it has to know which
102 modems it should access at which ports. This can be done with the setbaycom
103 utility. If you are only using one modem, you can also configure the
104 driver from the insmod command line (or by means of an option line in
105 ``/etc/modprobe.d/*.conf``).
106
107 Examples::
108
109 modprobe baycom_ser_fdx mode="ser12*" iobase=0x3f8 irq=4
110 sethdlc -i bcsf0 -p mode "ser12*" io 0x3f8 irq 4
111
112 Both lines configure the first port to drive a ser12 modem at the first
113 serial port (COM1 under DOS). The * in the mode parameter instructs the driver
114 to 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
119 Both lines configure the first port to drive a picpar modem at the
120 first parallel port (LPT1 under DOS). (Note: picpar implies
121 hardware DCD, par96 implies software DCD).
122
123 The channel access parameters can be set with sethdlc -a or kissparms.
124 Note that both utilities interpret the values slightly differently.
125
126
127 Hardware DCD versus Software DCD
128 ================================
129
130 To avoid collisions on the air, the driver must know when the channel is
131 busy. This is the task of the DCD circuitry/software. The driver may either
132 utilise a software DCD algorithm (options=1) or use a DCD signal from
133 the hardware (options=0).
134
135 ======= =================================================================
136 ser12 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
141 par96 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
147 picpar the picpar modem features a builtin DCD hardware, which is highly
148 recommended.
149 ======= =================================================================
150
151
152
153 Compatibility with the rest of the Linux kernel
154 ===============================================
155
156 The serial driver and the baycom serial drivers compete
157 for the same hardware resources. Of course only one driver can access a given
158 interface at a time. The serial driver grabs all interfaces it can find at
159 startup time. Therefore the baycom drivers subsequently won't be able to
160 access a serial port. You might therefore find it necessary to release
161 a 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
163 ports at startup, unless one is specified on the 'insmod' command line. Another
164 method to solve the problem is to compile all drivers as modules and
165 leave it to kmod to load the correct driver depending on the application.
166
167 The parallel port drivers (baycom_par, baycom_epp) now use the parport subsystem
168 to arbitrate the ports between different client drivers.
169
170 vy 73s de
171
172 Tom Sailer, sailer@ife.ee.ethz.ch
173
174 hb9jnx @ hb9w.ampr.org
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