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8.1 KiB
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192 lines
8.1 KiB
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.. SPDX-License-Identifier: GPL-2.0
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==============
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6pack Protocol
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==============
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This is the 6pack-mini-HOWTO, written by
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Andreas Könsgen DG3KQ
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:Internet: ajk@comnets.uni-bremen.de
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:AMPR-net: dg3kq@db0pra.ampr.org
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:AX.25: dg3kq@db0ach.#nrw.deu.eu
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Last update: April 7, 1998
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1. What is 6pack, and what are the advantages to KISS?
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======================================================
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6pack is a transmission protocol for data exchange between the PC and
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the TNC over a serial line. It can be used as an alternative to KISS.
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6pack has two major advantages:
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- The PC is given full control over the radio
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channel. Special control data is exchanged between the PC and the TNC so
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that the PC knows at any time if the TNC is receiving data, if a TNC
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buffer underrun or overrun has occurred, if the PTT is
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set and so on. This control data is processed at a higher priority than
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normal data, so a data stream can be interrupted at any time to issue an
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important event. This helps to improve the channel access and timing
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algorithms as everything is computed in the PC. It would even be possible
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to experiment with something completely different from the known CSMA and
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DAMA channel access methods.
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This kind of real-time control is especially important to supply several
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TNCs that are connected between each other and the PC by a daisy chain
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(however, this feature is not supported yet by the Linux 6pack driver).
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- Each packet transferred over the serial line is supplied with a checksum,
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so it is easy to detect errors due to problems on the serial line.
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Received packets that are corrupt are not passed on to the AX.25 layer.
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Damaged packets that the TNC has received from the PC are not transmitted.
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More details about 6pack are described in the file 6pack.ps that is located
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in the doc directory of the AX.25 utilities package.
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2. Who has developed the 6pack protocol?
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========================================
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The 6pack protocol has been developed by Ekki Plicht DF4OR, Henning Rech
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DF9IC and Gunter Jost DK7WJ. A driver for 6pack, written by Gunter Jost and
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Matthias Welwarsky DG2FEF, comes along with the PC version of FlexNet.
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They have also written a firmware for TNCs to perform the 6pack
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protocol (see section 4 below).
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3. Where can I get the latest version of 6pack for LinuX?
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=========================================================
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At the moment, the 6pack stuff can obtained via anonymous ftp from
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db0bm.automation.fh-aachen.de. In the directory /incoming/dg3kq,
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there is a file named 6pack.tgz.
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4. Preparing the TNC for 6pack operation
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========================================
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To be able to use 6pack, a special firmware for the TNC is needed. The EPROM
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of a newly bought TNC does not contain 6pack, so you will have to
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program an EPROM yourself. The image file for 6pack EPROMs should be
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available on any packet radio box where PC/FlexNet can be found. The name of
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the file is 6pack.bin. This file is copyrighted and maintained by the FlexNet
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team. It can be used under the terms of the license that comes along
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with PC/FlexNet. Please do not ask me about the internals of this file as I
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don't know anything about it. I used a textual description of the 6pack
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protocol to program the Linux driver.
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TNCs contain a 64kByte EPROM, the lower half of which is used for
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the firmware/KISS. The upper half is either empty or is sometimes
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programmed with software called TAPR. In the latter case, the TNC
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is supplied with a DIP switch so you can easily change between the
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two systems. When programming a new EPROM, one of the systems is replaced
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by 6pack. It is useful to replace TAPR, as this software is rarely used
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nowadays. If your TNC is not equipped with the switch mentioned above, you
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can build in one yourself that switches over the highest address pin
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of the EPROM between HIGH and LOW level. After having inserted the new EPROM
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and switched to 6pack, apply power to the TNC for a first test. The connect
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and the status LED are lit for about a second if the firmware initialises
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the TNC correctly.
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5. Building and installing the 6pack driver
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===========================================
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The driver has been tested with kernel version 2.1.90. Use with older
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kernels may lead to a compilation error because the interface to a kernel
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function has been changed in the 2.1.8x kernels.
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How to turn on 6pack support:
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=============================
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- In the linux kernel configuration program, select the code maturity level
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options menu and turn on the prompting for development drivers.
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- Select the amateur radio support menu and turn on the serial port 6pack
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driver.
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- Compile and install the kernel and the modules.
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To use the driver, the kissattach program delivered with the AX.25 utilities
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has to be modified.
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- Do a cd to the directory that holds the kissattach sources. Edit the
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kissattach.c file. At the top, insert the following lines::
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#ifndef N_6PACK
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#define N_6PACK (N_AX25+1)
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#endif
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Then find the line:
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int disc = N_AX25;
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and replace N_AX25 by N_6PACK.
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- Recompile kissattach. Rename it to spattach to avoid confusions.
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Installing the driver:
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----------------------
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- Do an insmod 6pack. Look at your /var/log/messages file to check if the
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module has printed its initialization message.
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- Do a spattach as you would launch kissattach when starting a KISS port.
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Check if the kernel prints the message '6pack: TNC found'.
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- From here, everything should work as if you were setting up a KISS port.
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The only difference is that the network device that represents
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the 6pack port is called sp instead of sl or ax. So, sp0 would be the
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first 6pack port.
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Although the driver has been tested on various platforms, I still declare it
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ALPHA. BE CAREFUL! Sync your disks before insmoding the 6pack module
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and spattaching. Watch out if your computer behaves strangely. Read section
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6 of this file about known problems.
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Note that the connect and status LEDs of the TNC are controlled in a
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different way than they are when the TNC is used with PC/FlexNet. When using
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FlexNet, the connect LED is on if there is a connection; the status LED is
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on if there is data in the buffer of the PC's AX.25 engine that has to be
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transmitted. Under Linux, the 6pack layer is beyond the AX.25 layer,
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so the 6pack driver doesn't know anything about connects or data that
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has not yet been transmitted. Therefore the LEDs are controlled
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as they are in KISS mode: The connect LED is turned on if data is transferred
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from the PC to the TNC over the serial line, the status LED if data is
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sent to the PC.
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6. Known problems
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=================
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When testing the driver with 2.0.3x kernels and
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operating with data rates on the radio channel of 9600 Baud or higher,
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the driver may, on certain systems, sometimes print the message '6pack:
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bad checksum', which is due to data loss if the other station sends two
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or more subsequent packets. I have been told that this is due to a problem
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with the serial driver of 2.0.3x kernels. I don't know yet if the problem
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still exists with 2.1.x kernels, as I have heard that the serial driver
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code has been changed with 2.1.x.
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When shutting down the sp interface with ifconfig, the kernel crashes if
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there is still an AX.25 connection left over which an IP connection was
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running, even if that IP connection is already closed. The problem does not
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occur when there is a bare AX.25 connection still running. I don't know if
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this is a problem of the 6pack driver or something else in the kernel.
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The driver has been tested as a module, not yet as a kernel-builtin driver.
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The 6pack protocol supports daisy-chaining of TNCs in a token ring, which is
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connected to one serial port of the PC. This feature is not implemented
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and at least at the moment I won't be able to do it because I do not have
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the opportunity to build a TNC daisy-chain and test it.
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Some of the comments in the source code are inaccurate. They are left from
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the SLIP/KISS driver, from which the 6pack driver has been derived.
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I haven't modified or removed them yet -- sorry! The code itself needs
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some cleaning and optimizing. This will be done in a later release.
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If you encounter a bug or if you have a question or suggestion concerning the
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driver, feel free to mail me, using the addresses given at the beginning of
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this file.
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Have fun!
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Andreas
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