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diff --git a/Documentation/networking/baycom.rst b/Documentation/networking/baycom.rst new file mode 100644 index 000000000000..fe2d010f0e86 --- /dev/null +++ b/Documentation/networking/baycom.rst @@ -0,0 +1,174 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============================== +Linux Drivers for Baycom Modems +=============================== + +Thomas M. Sailer, HB9JNX/AE4WA, <sailer@ife.ee.ethz.ch> + +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 |