1.. SPDX-License-Identifier: GPL-2.0 2 3=============================== 4Linux Drivers for Baycom Modems 5=============================== 6 7Thomas M. Sailer, HB9JNX/AE4WA, <sailer@ife.ee.ethz.ch> 8 9The drivers for the baycom modems have been split into 10separate drivers as they did not share any code, and the driver 11and device names have changed. 12 13This document describes the Linux Kernel Drivers for simple Baycom style 14amateur radio modems. 15 16The following drivers are available: 17==================================== 18 19baycom_ser_fdx: 20 This driver supports the SER12 modems either full or half duplex. 21 Its baud rate may be changed via the ``baud`` module parameter, 22 therefore it supports just about every bit bang modem on a 23 serial port. Its devices are called bcsf0 through bcsf3. 24 This is the recommended driver for SER12 type modems, 25 however if you have a broken UART clone that does not have working 26 delta status bits, you may try baycom_ser_hdx. 27 28baycom_ser_hdx: 29 This is an alternative driver for SER12 type modems. 30 It only supports half duplex, and only 1200 baud. Its devices 31 are called bcsh0 through bcsh3. Use this driver only if baycom_ser_fdx 32 does not work with your UART. 33 34baycom_par: 35 This driver supports the par96 and picpar modems. 36 Its devices are called bcp0 through bcp3. 37 38baycom_epp: 39 This driver supports the EPP modem. 40 Its devices are called bce0 through bce3. 41 This driver is work-in-progress. 42 43The following modems are supported: 44 45======= ======================================================================== 46ser12 This is a very simple 1200 baud AFSK modem. The modem consists only 47 of a modulator/demodulator chip, usually a TI TCM3105. The computer 48 is responsible for regenerating the receiver bit clock, as well as 49 for handling the HDLC protocol. The modem connects to a serial port, 50 hence the name. Since the serial port is not used as an async serial 51 port, the kernel driver for serial ports cannot be used, and this 52 driver only supports standard serial hardware (8250, 16450, 16550) 53 54par96 This is a modem for 9600 baud FSK compatible to the G3RUH standard. 55 The modem does all the filtering and regenerates the receiver clock. 56 Data is transferred from and to the PC via a shift register. 57 The shift register is filled with 16 bits and an interrupt is signalled. 58 The PC then empties the shift register in a burst. This modem connects 59 to the parallel port, hence the name. The modem leaves the 60 implementation of the HDLC protocol and the scrambler polynomial to 61 the PC. 62 63picpar This is a redesign of the par96 modem by Henning Rech, DF9IC. The modem 64 is protocol compatible to par96, but uses only three low power ICs 65 and can therefore be fed from the parallel port and does not require 66 an additional power supply. Furthermore, it incorporates a carrier 67 detect circuitry. 68 69EPP This is a high-speed modem adaptor that connects to an enhanced parallel 70 port. 71 72 Its target audience is users working over a high speed hub (76.8kbit/s). 73 74eppfpga This is a redesign of the EPP adaptor. 75======= ======================================================================== 76 77All of the above modems only support half duplex communications. However, 78the driver supports the KISS (see below) fullduplex command. It then simply 79starts to send as soon as there's a packet to transmit and does not care 80about DCD, i.e. it starts to send even if there's someone else on the channel. 81This command is required by some implementations of the DAMA channel 82access protocol. 83 84 85The Interface of the drivers 86============================ 87 88Unlike previous drivers, these drivers are no longer character devices, 89but they are now true kernel network interfaces. Installation is therefore 90simple. Once installed, four interfaces named bc{sf,sh,p,e}[0-3] are available. 91sethdlc from the ax25 utilities may be used to set driver states etc. 92Users of userland AX.25 stacks may use the net2kiss utility (also available 93in the ax25 utilities package) to convert packets of a network interface 94to a KISS stream on a pseudo tty. There's also a patch available from 95me for WAMPES which allows attaching a kernel network interface directly. 96 97 98Configuring the driver 99====================== 100 101Every time a driver is inserted into the kernel, it has to know which 102modems it should access at which ports. This can be done with the setbaycom 103utility. If you are only using one modem, you can also configure the 104driver from the insmod command line (or by means of an option line in 105``/etc/modprobe.d/*.conf``). 106 107Examples:: 108 109 modprobe baycom_ser_fdx mode="ser12*" iobase=0x3f8 irq=4 110 sethdlc -i bcsf0 -p mode "ser12*" io 0x3f8 irq 4 111 112Both lines configure the first port to drive a ser12 modem at the first 113serial port (COM1 under DOS). The * in the mode parameter instructs the driver 114to use the software DCD algorithm (see below):: 115 116 insmod baycom_par mode="picpar" iobase=0x378 117 sethdlc -i bcp0 -p mode "picpar" io 0x378 118 119Both lines configure the first port to drive a picpar modem at the 120first parallel port (LPT1 under DOS). (Note: picpar implies 121hardware DCD, par96 implies software DCD). 122 123The channel access parameters can be set with sethdlc -a or kissparms. 124Note that both utilities interpret the values slightly differently. 125 126 127Hardware DCD versus Software DCD 128================================ 129 130To avoid collisions on the air, the driver must know when the channel is 131busy. This is the task of the DCD circuitry/software. The driver may either 132utilise a software DCD algorithm (options=1) or use a DCD signal from 133the hardware (options=0). 134 135======= ================================================================= 136ser12 if software DCD is utilised, the radio's squelch should always be 137 open. It is highly recommended to use the software DCD algorithm, 138 as it is much faster than most hardware squelch circuitry. The 139 disadvantage is a slightly higher load on the system. 140 141par96 the software DCD algorithm for this type of modem is rather poor. 142 The modem simply does not provide enough information to implement 143 a reasonable DCD algorithm in software. Therefore, if your radio 144 feeds the DCD input of the PAR96 modem, the use of the hardware 145 DCD circuitry is recommended. 146 147picpar the picpar modem features a builtin DCD hardware, which is highly 148 recommended. 149======= ================================================================= 150 151 152 153Compatibility with the rest of the Linux kernel 154=============================================== 155 156The serial driver and the baycom serial drivers compete 157for the same hardware resources. Of course only one driver can access a given 158interface at a time. The serial driver grabs all interfaces it can find at 159startup time. Therefore the baycom drivers subsequently won't be able to 160access a serial port. You might therefore find it necessary to release 161a port owned by the serial driver with 'setserial /dev/ttyS# uart none', where 162# is the number of the interface. The baycom drivers do not reserve any 163ports at startup, unless one is specified on the 'insmod' command line. Another 164method to solve the problem is to compile all drivers as modules and 165leave it to kmod to load the correct driver depending on the application. 166 167The parallel port drivers (baycom_par, baycom_epp) now use the parport subsystem 168to arbitrate the ports between different client drivers. 169 170vy 73s de 171 172Tom Sailer, sailer@ife.ee.ethz.ch 173 174hb9jnx @ hb9w.ampr.org 175