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