159 lines
6.9 KiB
Plaintext
159 lines
6.9 KiB
Plaintext
LINUX DRIVERS FOR BAYCOM MODEMS
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Thomas M. Sailer, HB9JNX/AE4WA, <sailer@ife.ee.ethz.ch>
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!!NEW!! (04/98) The drivers for the baycom modems have been split into
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separate drivers as they did not share any code, and the driver
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and device names have changed.
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This document describes the Linux Kernel Drivers for simple Baycom style
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amateur radio modems.
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The following drivers are available:
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baycom_ser_fdx:
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This driver supports the SER12 modems either full or half duplex.
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Its baud rate may be changed via the `baud' module parameter,
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therefore it supports just about every bit bang modem on a
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serial port. Its devices are called bcsf0 through bcsf3.
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This is the recommended driver for SER12 type modems,
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however if you have a broken UART clone that does not have working
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delta status bits, you may try baycom_ser_hdx.
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baycom_ser_hdx:
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This is an alternative driver for SER12 type modems.
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It only supports half duplex, and only 1200 baud. Its devices
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are called bcsh0 through bcsh3. Use this driver only if baycom_ser_fdx
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does not work with your UART.
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baycom_par:
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This driver supports the par96 and picpar modems.
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Its devices are called bcp0 through bcp3.
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baycom_epp:
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This driver supports the EPP modem.
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Its devices are called bce0 through bce3.
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This driver is work-in-progress.
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The following modems are supported:
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ser12: This is a very simple 1200 baud AFSK modem. The modem consists only
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of a modulator/demodulator chip, usually a TI TCM3105. The computer
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is responsible for regenerating the receiver bit clock, as well as
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for handling the HDLC protocol. The modem connects to a serial port,
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hence the name. Since the serial port is not used as an async serial
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port, the kernel driver for serial ports cannot be used, and this
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driver only supports standard serial hardware (8250, 16450, 16550)
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par96: This is a modem for 9600 baud FSK compatible to the G3RUH standard.
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The modem does all the filtering and regenerates the receiver clock.
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Data is transferred from and to the PC via a shift register.
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The shift register is filled with 16 bits and an interrupt is signalled.
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The PC then empties the shift register in a burst. This modem connects
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to the parallel port, hence the name. The modem leaves the
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implementation of the HDLC protocol and the scrambler polynomial to
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the PC.
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picpar: This is a redesign of the par96 modem by Henning Rech, DF9IC. The modem
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is protocol compatible to par96, but uses only three low power ICs
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and can therefore be fed from the parallel port and does not require
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an additional power supply. Furthermore, it incorporates a carrier
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detect circuitry.
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EPP: This is a high-speed modem adaptor that connects to an enhanced parallel port.
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Its target audience is users working over a high speed hub (76.8kbit/s).
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eppfpga: This is a redesign of the EPP adaptor.
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All of the above modems only support half duplex communications. However,
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the driver supports the KISS (see below) fullduplex command. It then simply
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starts to send as soon as there's a packet to transmit and does not care
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about DCD, i.e. it starts to send even if there's someone else on the channel.
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This command is required by some implementations of the DAMA channel
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access protocol.
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The Interface of the drivers
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Unlike previous drivers, these drivers are no longer character devices,
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but they are now true kernel network interfaces. Installation is therefore
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simple. Once installed, four interfaces named bc{sf,sh,p,e}[0-3] are available.
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sethdlc from the ax25 utilities may be used to set driver states etc.
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Users of userland AX.25 stacks may use the net2kiss utility (also available
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in the ax25 utilities package) to convert packets of a network interface
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to a KISS stream on a pseudo tty. There's also a patch available from
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me for WAMPES which allows attaching a kernel network interface directly.
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Configuring the driver
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Every time a driver is inserted into the kernel, it has to know which
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modems it should access at which ports. This can be done with the setbaycom
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utility. If you are only using one modem, you can also configure the
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driver from the insmod command line (or by means of an option line in
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/etc/modprobe.conf).
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Examples:
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modprobe baycom_ser_fdx mode="ser12*" iobase=0x3f8 irq=4
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sethdlc -i bcsf0 -p mode "ser12*" io 0x3f8 irq 4
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Both lines configure the first port to drive a ser12 modem at the first
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serial port (COM1 under DOS). The * in the mode parameter instructs the driver to use
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the software DCD algorithm (see below).
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insmod baycom_par mode="picpar" iobase=0x378
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sethdlc -i bcp0 -p mode "picpar" io 0x378
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Both lines configure the first port to drive a picpar modem at the
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first parallel port (LPT1 under DOS). (Note: picpar implies
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hardware DCD, par96 implies software DCD).
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The channel access parameters can be set with sethdlc -a or kissparms.
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Note that both utilities interpret the values slightly differently.
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Hardware DCD versus Software DCD
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To avoid collisions on the air, the driver must know when the channel is
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busy. This is the task of the DCD circuitry/software. The driver may either
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utilise a software DCD algorithm (options=1) or use a DCD signal from
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the hardware (options=0).
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ser12: if software DCD is utilised, the radio's squelch should always be
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open. It is highly recommended to use the software DCD algorithm,
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as it is much faster than most hardware squelch circuitry. The
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disadvantage is a slightly higher load on the system.
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par96: the software DCD algorithm for this type of modem is rather poor.
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The modem simply does not provide enough information to implement
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a reasonable DCD algorithm in software. Therefore, if your radio
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feeds the DCD input of the PAR96 modem, the use of the hardware
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DCD circuitry is recommended.
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picpar: the picpar modem features a builtin DCD hardware, which is highly
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recommended.
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Compatibility with the rest of the Linux kernel
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The serial driver and the baycom serial drivers compete
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for the same hardware resources. Of course only one driver can access a given
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interface at a time. The serial driver grabs all interfaces it can find at
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startup time. Therefore the baycom drivers subsequently won't be able to
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access a serial port. You might therefore find it necessary to release
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a port owned by the serial driver with 'setserial /dev/ttyS# uart none', where
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# is the number of the interface. The baycom drivers do not reserve any
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ports at startup, unless one is specified on the 'insmod' command line. Another
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method to solve the problem is to compile all drivers as modules and
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leave it to kmod to load the correct driver depending on the application.
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The parallel port drivers (baycom_par, baycom_epp) now use the parport subsystem
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to arbitrate the ports between different client drivers.
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vy 73s de
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Tom Sailer, sailer@ife.ee.ethz.ch
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hb9jnx @ hb9w.ampr.org
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