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191 lines
8.1 KiB
191 lines
8.1 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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6pack Protocol |
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This is the 6pack-mini-HOWTO, written by |
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Andreas Könsgen DG3KQ |
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:Internet: [email protected] |
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:AMPR-net: [email protected] |
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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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