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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.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 |
159 |
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