1                    LINUX DRIVERS FOR BAYCOM MODEMS
   3       Thomas M. Sailer, HB9JNX/AE4WA, <>
   5!!NEW!! (04/98) The drivers for the baycom modems have been split into
   6separate drivers as they did not share any code, and the driver
   7and device names have changed.
   9This document describes the Linux Kernel Drivers for simple Baycom style
  10amateur radio modems. 
  12The following drivers are available:
  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. 
  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.
  30  This driver supports the par96 and picpar modems.
  31  Its devices are called bcp0 through bcp3.
  34  This driver supports the EPP modem.
  35  Its devices are called bce0 through bce3.
  36  This driver is work-in-progress.
  38The following modems are supported:
  40ser12:  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)
  48par96:  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.
  57picpar: 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.
  63EPP:    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).
  66eppfpga: This is a redesign of the EPP adaptor.
  70All of the above modems only support half duplex communications. However,
  71the driver supports the KISS (see below) fullduplex command. It then simply
  72starts to send as soon as there's a packet to transmit and does not care
  73about DCD, i.e. it starts to send even if there's someone else on the channel.
  74This command is required by some implementations of the DAMA channel 
  75access protocol.
  78The Interface of the drivers
  80Unlike previous drivers, these drivers are no longer character devices,
  81but they are now true kernel network interfaces. Installation is therefore
  82simple. Once installed, four interfaces named bc{sf,sh,p,e}[0-3] are available.
  83sethdlc from the ax25 utilities may be used to set driver states etc.
  84Users of userland AX.25 stacks may use the net2kiss utility (also available
  85in the ax25 utilities package) to convert packets of a network interface
  86to a KISS stream on a pseudo tty. There's also a patch available from
  87me for WAMPES which allows attaching a kernel network interface directly.
  90Configuring the driver
  92Every time a driver is inserted into the kernel, it has to know which
  93modems it should access at which ports. This can be done with the setbaycom
  94utility. If you are only using one modem, you can also configure the
  95driver from the insmod command line (or by means of an option line in
  99  modprobe baycom_ser_fdx mode="ser12*" iobase=0x3f8 irq=4
 100  sethdlc -i bcsf0 -p mode "ser12*" io 0x3f8 irq 4
 102Both lines configure the first port to drive a ser12 modem at the first
 103serial port (COM1 under DOS). The * in the mode parameter instructs the driver to use
 104the software DCD algorithm (see below).
 106  insmod baycom_par mode="picpar" iobase=0x378
 107  sethdlc -i bcp0 -p mode "picpar" io 0x378
 109Both lines configure the first port to drive a picpar modem at the
 110first parallel port (LPT1 under DOS). (Note: picpar implies
 111hardware DCD, par96 implies software DCD).
 113The channel access parameters can be set with sethdlc -a or kissparms.
 114Note that both utilities interpret the values slightly differently.
 117Hardware DCD versus Software DCD
 119To avoid collisions on the air, the driver must know when the channel is
 120busy. This is the task of the DCD circuitry/software. The driver may either
 121utilise a software DCD algorithm (options=1) or use a DCD signal from
 122the hardware (options=0).
 124ser12:  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.
 129par96:  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.
 135picpar: the picpar modem features a builtin DCD hardware, which is highly
 136        recommended.
 140Compatibility with the rest of the Linux kernel
 142The serial driver and the baycom serial drivers compete
 143for the same hardware resources. Of course only one driver can access a given
 144interface at a time. The serial driver grabs all interfaces it can find at
 145startup time. Therefore the baycom drivers subsequently won't be able to
 146access a serial port. You might therefore find it necessary to release
 147a 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
 149ports at startup, unless one is specified on the 'insmod' command line. Another
 150method to solve the problem is to compile all drivers as modules and
 151leave it to kmod to load the correct driver depending on the application.
 153The parallel port drivers (baycom_par, baycom_epp) now use the parport subsystem
 154to arbitrate the ports between different client drivers.
 156vy 73s de
 157Tom Sailer,
 158hb9jnx @
 159 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.