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Based on kernel version 2.6.34. Page generated on 2010-05-31 16:03 EST.

1	This is the 6pack-mini-HOWTO, written by
2	
3	Andreas Könsgen DG3KQ
4	Internet: ajk[AT]comnets.uni-bremen[DOT]de
5	AMPR-net: dg3kq[AT]db0pra.ampr[DOT]org
6	AX.25:    dg3kq[AT]db0ach.#nrw.deu[DOT]eu
7	
8	Last update: April 7, 1998
9	
10	1. What is 6pack, and what are the advantages to KISS?
11	
12	6pack is a transmission protocol for data exchange between the PC and
13	the TNC over a serial line. It can be used as an alternative to KISS.
14	
15	6pack 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).
29	
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.
34	
35	More details about 6pack are described in the file 6pack.ps that is located
36	in the doc directory of the AX.25 utilities package.
37	
38	2. Who has developed the 6pack protocol?
39	
40	The 6pack protocol has been developed by Ekki Plicht DF4OR, Henning Rech
41	DF9IC and Gunter Jost DK7WJ. A driver for 6pack, written by Gunter Jost and
42	Matthias Welwarsky DG2FEF, comes along with the PC version of FlexNet.
43	They have also written a firmware for TNCs to perform the 6pack
44	protocol (see section 4 below).
45	
46	3. Where can I get the latest version of 6pack for LinuX?
47	
48	At the moment, the 6pack stuff can obtained via anonymous ftp from
49	db0bm.automation.fh-aachen.de. In the directory /incoming/dg3kq,
50	there is a file named 6pack.tgz.
51	
52	4. Preparing the TNC for 6pack operation
53	
54	To be able to use 6pack, a special firmware for the TNC is needed. The EPROM
55	of a newly bought TNC does not contain 6pack, so you will have to
56	program an EPROM yourself. The image file for 6pack EPROMs should be
57	available on any packet radio box where PC/FlexNet can be found. The name of
58	the file is 6pack.bin. This file is copyrighted and maintained by the FlexNet
59	team. It can be used under the terms of the license that comes along
60	with PC/FlexNet. Please do not ask me about the internals of this file as I
61	don't know anything about it. I used a textual description of the 6pack
62	protocol to program the Linux driver.
63	
64	TNCs contain a 64kByte EPROM, the lower half of which is used for
65	the firmware/KISS. The upper half is either empty or is sometimes
66	programmed with software called TAPR. In the latter case, the TNC
67	is supplied with a DIP switch so you can easily change between the
68	two systems. When programming a new EPROM, one of the systems is replaced
69	by 6pack. It is useful to replace TAPR, as this software is rarely used
70	nowadays. If your TNC is not equipped with the switch mentioned above, you
71	can build in one yourself that switches over the highest address pin
72	of the EPROM between HIGH and LOW level. After having inserted the new EPROM
73	and switched to 6pack, apply power to the TNC for a first test. The connect
74	and the status LED are lit for about a second if the firmware initialises
75	the TNC correctly.
76	
77	5. Building and installing the 6pack driver
78	
79	The driver has been tested with kernel version 2.1.90. Use with older
80	kernels may lead to a compilation error because the interface to a kernel
81	function has been changed in the 2.1.8x kernels.
82	
83	How to turn on 6pack support:
84	
85	- In the linux kernel configuration program, select the code maturity level
86	  options menu and turn on the prompting for development drivers.
87	
88	- Select the amateur radio support menu and turn on the serial port 6pack
89	  driver.
90	
91	- Compile and install the kernel and the modules.
92	
93	To use the driver, the kissattach program delivered with the AX.25 utilities
94	has to be modified.
95	
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:
98	
99	  #ifndef N_6PACK
100	  #define N_6PACK (N_AX25+1)
101	  #endif
102	
103	  Then find the line
104	   
105	  int disc = N_AX25;
106	
107	  and replace N_AX25 by N_6PACK.
108	
109	- Recompile kissattach. Rename it to spattach to avoid confusions.
110	
111	Installing the driver:
112	
113	- Do an insmod 6pack. Look at your /var/log/messages file to check if the 
114	  module has printed its initialization message.
115	
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'. 
118	
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.
123	
124	Although the driver has been tested on various platforms, I still declare it
125	ALPHA. BE CAREFUL! Sync your disks before insmoding the 6pack module
126	and spattaching. Watch out if your computer behaves strangely. Read section
127	6 of this file about known problems.
128	
129	Note that the connect and status LEDs of the TNC are controlled in a
130	different way than they are when the TNC is used with PC/FlexNet. When using
131	FlexNet, the connect LED is on if there is a connection; the status LED is
132	on if there is data in the buffer of the PC's AX.25 engine that has to be
133	transmitted. Under Linux, the 6pack layer is beyond the AX.25 layer,
134	so the 6pack driver doesn't know anything about connects or data that
135	has not yet been transmitted. Therefore the LEDs are controlled
136	as they are in KISS mode: The connect LED is turned on if data is transferred
137	from the PC to the TNC over the serial line, the status LED if data is
138	sent to the PC.
139	
140	6. Known problems
141	
142	When testing the driver with 2.0.3x kernels and
143	operating with data rates on the radio channel of 9600 Baud or higher,
144	the driver may, on certain systems, sometimes print the message '6pack:
145	bad checksum', which is due to data loss if the other station sends two
146	or more subsequent packets. I have been told that this is due to a problem
147	with the serial driver of 2.0.3x kernels. I don't know yet if the problem
148	still exists with 2.1.x kernels, as I have heard that the serial driver
149	code has been changed with 2.1.x.
150	
151	When shutting down the sp interface with ifconfig, the kernel crashes if
152	there is still an AX.25 connection left over which an IP connection was
153	running, even if that IP connection is already closed. The problem does not
154	occur when there is a bare AX.25 connection still running. I don't know if
155	this is a problem of the 6pack driver or something else in the kernel.
156	
157	The driver has been tested as a module, not yet as a kernel-builtin driver.
158	
159	The 6pack protocol supports daisy-chaining of TNCs in a token ring, which is
160	connected to one serial port of the PC. This feature is not implemented
161	and at least at the moment I won't be able to do it because I do not have
162	the opportunity to build a TNC daisy-chain and test it.
163	
164	Some of the comments in the source code are inaccurate. They are left from
165	the SLIP/KISS driver, from which the 6pack driver has been derived.
166	I haven't modified or removed them yet -- sorry! The code itself needs
167	some cleaning and optimizing. This will be done in a later release.
168	
169	If you encounter a bug or if you have a question or suggestion concerning the
170	driver, feel free to mail me, using the addresses given at the beginning of
171	this file.
172	
173	Have fun!
174	
175	Andreas
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