1This is the 6pack-mini-HOWTO, written by
   3Andreas K\xC3\xB6nsgen DG3KQ
   8Last update: April 7, 1998
  101. What is 6pack, and what are the advantages to KISS?
  126pack is a transmission protocol for data exchange between the PC and
  13the TNC over a serial line. It can be used as an alternative to KISS.
  156pack has two major advantages:
  16- The PC is given full control over the radio
  17  channel. Special control data is exchanged between the PC and the TNC so
  18  that the PC knows at any time if the TNC is receiving data, if a TNC
  19  buffer underrun or overrun has occurred, if the PTT is
  20  set and so on. This control data is processed at a higher priority than
  21  normal data, so a data stream can be interrupted at any time to issue an
  22  important event. This helps to improve the channel access and timing 
  23  algorithms as everything is computed in the PC. It would even be possible 
  24  to experiment with something completely different from the known CSMA and 
  25  DAMA channel access methods.
  26  This kind of real-time control is especially important to supply several
  27  TNCs that are connected between each other and the PC by a daisy chain
  28  (however, this feature is not supported yet by the Linux 6pack driver).
  30- Each packet transferred over the serial line is supplied with a checksum,
  31  so it is easy to detect errors due to problems on the serial line.
  32  Received packets that are corrupt are not passed on to the AX.25 layer.
  33  Damaged packets that the TNC has received from the PC are not transmitted.
  35More details about 6pack are described in the file that is located
  36in the doc directory of the AX.25 utilities package.
  382. Who has developed the 6pack protocol?
  40The 6pack protocol has been developed by Ekki Plicht DF4OR, Henning Rech
  41DF9IC and Gunter Jost DK7WJ. A driver for 6pack, written by Gunter Jost and
  42Matthias Welwarsky DG2FEF, comes along with the PC version of FlexNet.
  43They have also written a firmware for TNCs to perform the 6pack
  44protocol (see section 4 below).
  463. Where can I get the latest version of 6pack for LinuX?
  48At the moment, the 6pack stuff can obtained via anonymous ftp from In the directory /incoming/dg3kq,
  50there is a file named 6pack.tgz.
  524. Preparing the TNC for 6pack operation
  54To be able to use 6pack, a special firmware for the TNC is needed. The EPROM
  55of a newly bought TNC does not contain 6pack, so you will have to
  56program an EPROM yourself. The image file for 6pack EPROMs should be
  57available on any packet radio box where PC/FlexNet can be found. The name of
  58the file is 6pack.bin. This file is copyrighted and maintained by the FlexNet
  59team. It can be used under the terms of the license that comes along
  60with PC/FlexNet. Please do not ask me about the internals of this file as I
  61don't know anything about it. I used a textual description of the 6pack
  62protocol to program the Linux driver.
  64TNCs contain a 64kByte EPROM, the lower half of which is used for
  65the firmware/KISS. The upper half is either empty or is sometimes
  66programmed with software called TAPR. In the latter case, the TNC
  67is supplied with a DIP switch so you can easily change between the
  68two systems. When programming a new EPROM, one of the systems is replaced
  69by 6pack. It is useful to replace TAPR, as this software is rarely used
  70nowadays. If your TNC is not equipped with the switch mentioned above, you
  71can build in one yourself that switches over the highest address pin
  72of the EPROM between HIGH and LOW level. After having inserted the new EPROM
  73and switched to 6pack, apply power to the TNC for a first test. The connect
  74and the status LED are lit for about a second if the firmware initialises
  75the TNC correctly.
  775. Building and installing the 6pack driver
  79The driver has been tested with kernel version 2.1.90. Use with older
  80kernels may lead to a compilation error because the interface to a kernel
  81function has been changed in the 2.1.8x kernels.
  83How to turn on 6pack support:
  85- In the linux kernel configuration program, select the code maturity level
  86  options menu and turn on the prompting for development drivers.
  88- Select the amateur radio support menu and turn on the serial port 6pack
  89  driver.
  91- Compile and install the kernel and the modules.
  93To use the driver, the kissattach program delivered with the AX.25 utilities
  94has to be modified.
  96- Do a cd to the directory that holds the kissattach sources. Edit the
  97  kissattach.c file. At the top, insert the following lines:
  99  #ifndef N_6PACK
 100  #define N_6PACK (N_AX25+1)
 101  #endif
 103  Then find the line
 105  int disc = N_AX25;
 107  and replace N_AX25 by N_6PACK.
 109- Recompile kissattach. Rename it to spattach to avoid confusions.
 111Installing the driver:
 113- Do an insmod 6pack. Look at your /var/log/messages file to check if the 
 114  module has printed its initialization message.
 116- Do a spattach as you would launch kissattach when starting a KISS port.
 117  Check if the kernel prints the message '6pack: TNC found'. 
 119- From here, everything should work as if you were setting up a KISS port.
 120  The only difference is that the network device that represents
 121  the 6pack port is called sp instead of sl or ax. So, sp0 would be the
 122  first 6pack port.
 124Although the driver has been tested on various platforms, I still declare it
 125ALPHA. BE CAREFUL! Sync your disks before insmoding the 6pack module
 126and spattaching. Watch out if your computer behaves strangely. Read section
 1276 of this file about known problems.
 129Note that the connect and status LEDs of the TNC are controlled in a
 130different way than they are when the TNC is used with PC/FlexNet. When using
 131FlexNet, the connect LED is on if there is a connection; the status LED is
 132on if there is data in the buffer of the PC's AX.25 engine that has to be
 133transmitted. Under Linux, the 6pack layer is beyond the AX.25 layer,
 134so the 6pack driver doesn't know anything about connects or data that
 135has not yet been transmitted. Therefore the LEDs are controlled
 136as they are in KISS mode: The connect LED is turned on if data is transferred
 137from the PC to the TNC over the serial line, the status LED if data is
 138sent to the PC.
 1406. Known problems
 142When testing the driver with 2.0.3x kernels and
 143operating with data rates on the radio channel of 9600 Baud or higher,
 144the driver may, on certain systems, sometimes print the message '6pack:
 145bad checksum', which is due to data loss if the other station sends two
 146or more subsequent packets. I have been told that this is due to a problem
 147with the serial driver of 2.0.3x kernels. I don't know yet if the problem
 148still exists with 2.1.x kernels, as I have heard that the serial driver
 149code has been changed with 2.1.x.
 151When shutting down the sp interface with ifconfig, the kernel crashes if
 152there is still an AX.25 connection left over which an IP connection was
 153running, even if that IP connection is already closed. The problem does not
 154occur when there is a bare AX.25 connection still running. I don't know if
 155this is a problem of the 6pack driver or something else in the kernel.
 157The driver has been tested as a module, not yet as a kernel-builtin driver.
 159The 6pack protocol supports daisy-chaining of TNCs in a token ring, which is
 160connected to one serial port of the PC. This feature is not implemented
 161and at least at the moment I won't be able to do it because I do not have
 162the opportunity to build a TNC daisy-chain and test it.
 164Some of the comments in the source code are inaccurate. They are left from
 165the SLIP/KISS driver, from which the 6pack driver has been derived.
 166I haven't modified or removed them yet -- sorry! The code itself needs
 167some cleaning and optimizing. This will be done in a later release.
 169If you encounter a bug or if you have a question or suggestion concerning the
 170driver, feel free to mail me, using the addresses given at the beginning of
 171this file.
 173Have fun!
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