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Based on kernel version 3.9. Page generated on 2013-05-02 23:10 EST.

1			    LINUX DRIVERS FOR BAYCOM MODEMS
2	
3	       Thomas M. Sailer, HB9JNX/AE4WA, <sailer@ife.ee.ethz.ch>
4	
5	!!NEW!! (04/98) The drivers for the baycom modems have been split into
6	separate drivers as they did not share any code, and the driver
7	and device names have changed.
8	
9	This document describes the Linux Kernel Drivers for simple Baycom style
10	amateur radio modems. 
11	
12	The following drivers are available:
13	
14	baycom_ser_fdx:
15	  This driver supports the SER12 modems either full or half duplex.
16	  Its baud rate may be changed via the `baud' module parameter,
17	  therefore it supports just about every bit bang modem on a
18	  serial port. Its devices are called bcsf0 through bcsf3.
19	  This is the recommended driver for SER12 type modems,
20	  however if you have a broken UART clone that does not have working
21	  delta status bits, you may try baycom_ser_hdx. 
22	
23	baycom_ser_hdx: 
24	  This is an alternative driver for SER12 type modems.
25	  It only supports half duplex, and only 1200 baud. Its devices
26	  are called bcsh0 through bcsh3. Use this driver only if baycom_ser_fdx
27	  does not work with your UART.
28	
29	baycom_par:
30	  This driver supports the par96 and picpar modems.
31	  Its devices are called bcp0 through bcp3.
32	
33	baycom_epp:
34	  This driver supports the EPP modem.
35	  Its devices are called bce0 through bce3.
36	  This driver is work-in-progress.
37	
38	The following modems are supported:
39	
40	ser12:  This is a very simple 1200 baud AFSK modem. The modem consists only
41	        of a modulator/demodulator chip, usually a TI TCM3105. The computer
42	        is responsible for regenerating the receiver bit clock, as well as
43	        for handling the HDLC protocol. The modem connects to a serial port,
44	        hence the name. Since the serial port is not used as an async serial
45	        port, the kernel driver for serial ports cannot be used, and this
46	        driver only supports standard serial hardware (8250, 16450, 16550)
47	
48	par96:  This is a modem for 9600 baud FSK compatible to the G3RUH standard.
49	        The modem does all the filtering and regenerates the receiver clock.
50	        Data is transferred from and to the PC via a shift register.
51	        The shift register is filled with 16 bits and an interrupt is signalled.
52	        The PC then empties the shift register in a burst. This modem connects
53	        to the parallel port, hence the name. The modem leaves the 
54	        implementation of the HDLC protocol and the scrambler polynomial to
55	        the PC.
56	
57	picpar: This is a redesign of the par96 modem by Henning Rech, DF9IC. The modem
58	        is protocol compatible to par96, but uses only three low power ICs
59	        and can therefore be fed from the parallel port and does not require
60	        an additional power supply. Furthermore, it incorporates a carrier
61	        detect circuitry.
62	
63	EPP:    This is a high-speed modem adaptor that connects to an enhanced parallel port.
64	        Its target audience is users working over a high speed hub (76.8kbit/s).
65	
66	eppfpga: This is a redesign of the EPP adaptor.
67	
68	
69	
70	All of the above modems only support half duplex communications. However,
71	the driver supports the KISS (see below) fullduplex command. It then simply
72	starts to send as soon as there's a packet to transmit and does not care
73	about DCD, i.e. it starts to send even if there's someone else on the channel.
74	This command is required by some implementations of the DAMA channel 
75	access protocol.
76	
77	
78	The Interface of the drivers
79	
80	Unlike previous drivers, these drivers are no longer character devices,
81	but they are now true kernel network interfaces. Installation is therefore
82	simple. Once installed, four interfaces named bc{sf,sh,p,e}[0-3] are available.
83	sethdlc from the ax25 utilities may be used to set driver states etc.
84	Users of userland AX.25 stacks may use the net2kiss utility (also available
85	in the ax25 utilities package) to convert packets of a network interface
86	to a KISS stream on a pseudo tty. There's also a patch available from
87	me for WAMPES which allows attaching a kernel network interface directly.
88	
89	
90	Configuring the driver
91	
92	Every time a driver is inserted into the kernel, it has to know which
93	modems it should access at which ports. This can be done with the setbaycom
94	utility. If you are only using one modem, you can also configure the
95	driver from the insmod command line (or by means of an option line in
96	/etc/modprobe.d/*.conf).
97	
98	Examples:
99	  modprobe baycom_ser_fdx mode="ser12*" iobase=0x3f8 irq=4
100	  sethdlc -i bcsf0 -p mode "ser12*" io 0x3f8 irq 4
101	
102	Both lines configure the first port to drive a ser12 modem at the first
103	serial port (COM1 under DOS). The * in the mode parameter instructs the driver to use
104	the software DCD algorithm (see below).
105	
106	  insmod baycom_par mode="picpar" iobase=0x378
107	  sethdlc -i bcp0 -p mode "picpar" io 0x378
108	
109	Both lines configure the first port to drive a picpar modem at the
110	first parallel port (LPT1 under DOS). (Note: picpar implies
111	hardware DCD, par96 implies software DCD).
112	
113	The channel access parameters can be set with sethdlc -a or kissparms.
114	Note that both utilities interpret the values slightly differently.
115	
116	
117	Hardware DCD versus Software DCD
118	
119	To avoid collisions on the air, the driver must know when the channel is
120	busy. This is the task of the DCD circuitry/software. The driver may either
121	utilise a software DCD algorithm (options=1) or use a DCD signal from
122	the hardware (options=0).
123	
124	ser12:  if software DCD is utilised, the radio's squelch should always be
125	        open. It is highly recommended to use the software DCD algorithm,
126	        as it is much faster than most hardware squelch circuitry. The
127	        disadvantage is a slightly higher load on the system.
128	
129	par96:  the software DCD algorithm for this type of modem is rather poor.
130	        The modem simply does not provide enough information to implement
131	        a reasonable DCD algorithm in software. Therefore, if your radio
132	        feeds the DCD input of the PAR96 modem, the use of the hardware
133	        DCD circuitry is recommended.
134	
135	picpar: the picpar modem features a builtin DCD hardware, which is highly
136	        recommended.
137	
138	
139	
140	Compatibility with the rest of the Linux kernel
141	
142	The serial driver and the baycom serial drivers compete
143	for the same hardware resources. Of course only one driver can access a given
144	interface at a time. The serial driver grabs all interfaces it can find at
145	startup time. Therefore the baycom drivers subsequently won't be able to
146	access a serial port. You might therefore find it necessary to release
147	a port owned by the serial driver with 'setserial /dev/ttyS# uart none', where
148	# is the number of the interface. The baycom drivers do not reserve any
149	ports at startup, unless one is specified on the 'insmod' command line. Another
150	method to solve the problem is to compile all drivers as modules and
151	leave it to kmod to load the correct driver depending on the application.
152	
153	The parallel port drivers (baycom_par, baycom_epp) now use the parport subsystem
154	to arbitrate the ports between different client drivers.
155	
156	vy 73s de
157	Tom Sailer, sailer@ife.ee.ethz.ch
158	hb9jnx @ hb9w.ampr.org
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