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Amiga Collections: Amiga Amateur Radio User Group
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AARUG UK #81 (199x)(Amiga Amateur Radio User Group UK)(PD)[WB][G4DCV].zip
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AARUG UK #81 (199x)(Amiga Amateur Radio User Group UK)(PD)[WB][G4DCV].adf
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DisView
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ATTACH
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1995-05-29
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====== DISview [518]
attach
======
This section details the 'attach' commands for the various
hardware and software interface drivers. A list of the
available types on a particular release may be obtained with the
'attach ?' command.
Some parameters are accepted by several drivers. They are:
----------------
<rx_buffer_size>
----------------
For asynchronous devices (e.g. COM ports operating in SLIP/PPP
mode) this parameter specifies the size of the receiver's ring
buffer. It should be large enough to hold incoming data at full
line speed.
Another important consideration is that the more recent versions
of NET improve interrupt response by maintaining a special pool
of buffers for use by the receive routines. This limits
<rx_buffer_size>; in fact, attempting to set a larger value may
cause the driver not to work at all. This situation can be
detected by giving the 'memory status' command and looking for
non-zero count of "Ibuffail" events, although these events can
also occur occasionally during normal operation.
-----------
<interface>
-----------
The name to be assigned to this interface. It is an arbitrary
character string, and is used to refer to the interface by
many commands, including:
attach detach dialer ifconfig ip filter
param ppp tip trace
In Demon's NET distribution, the standard interface name for
a COM port is 'sl0' (i.e. letter "ess", letter "ell", digit
zero), standing for 'serial link zero'. (N.B. the interface
name need not relate directly to the COM port number -- for
example, 'sl0' could refer to COM1 or COM2 or COM3, etc).
-----------
<ioaddress>
-----------
The base address of the interface's control registers, in
hexadecimal.
--------
<vector>
--------
The interface's hardware interrupt (IRQ) vector, in hexadecimal.
Standard values for serial ports on the IBM PC and clones for
<ioaddress> and <vector> are as follows:
<ioaddress> <vector>
----------- --------
COM1: 0x3f8 4
COM2: 0x2f8 3
COM3: 0x3e8 4
COM4: 0x2e8 3
If the port uses a 16550A chip, it will be detected
automatically and the FIFOs enabled.
-----
<mtu>
-----
The Maximum Transmission Unit (MTU) size, in bytes. Datagrams
larger than this limit will be fragmented at the IP layer into
smaller pieces.
IP-level fragmentation often makes it possible to interconnect
two dissimilar networks, but it is best avoided whenever
possible. One reason is that when a single IP fragment is lost,
all other fragments belonging to the same datagram are
effectively also lost and the entire datagram must be
retransmitted by the source.
Even without loss, fragments require the allocation of temporary
buffer memory at the destination, and it is never easy to decide
how long to wait for missing fragments before giving up and
discarding those that have already arrived. A reassembly timer
controls this process. (See the 'ip rtimer' command).
Most subnetworks that carry IP have MTUs of 576 bytes or more, so
interconnecting them with subnetworks having smaller values can
result in considerable fragmentation. For this reason, IP
implementors working with links or subnets having unusually small
packet size limits are encouraged to use transparent
fragmentation, that is, to devise schemes to break up large IP
datagrams into a sequence of link or subnet frames that are
immediately reassembled on the other end of the link or subnet
into the original, whole IP datagram without the use of IP-level
fragmentation.
Each fragment of a datagram has its own IP header, and is handled
by the network as if it were a distinct IP datagram. When it
arrives at the destination it is held by the IP layer until all
the other fragments belonging to the original datagram have
arrived. Then they are reassembled back into the complete,
original IP datagram.
The minimum acceptable interface MTU is 28 bytes: 20 bytes for
the IP header, plus 8 bytes of data.
There is no default MTU in NET; it must be explicitly specified
for each interface as part of the 'attach' command.
TCP/IP header overhead considerations apply when choosing an MTU.
However, certain subnetwork types supported by NET have well-
established MTUs, and these should always be used unless you know
what you're doing. The recommended MTUs for these network types
are:
Ethernet: 1500 bytes
ARCNET: 508 bytes
PPP: The MTU for PPP is automatically negotiated, and
defaults to 1500 bytes.
Other subnet types, including SLIP, are not as well
standardized.
SLIP: Has no official MTU, but the most common implementation
(for BSD UNIX) uses an MTU of 1006 bytes. Although NET has no
hard-wired limit on the size of a received SLIP frame, this is
not true for other systems. Interoperability problems may
therefore result if larger MTUs are used in NET.
-------
<speed>
-------
The speed on the NET serial link (e.g. between the computer
running NET and the modem) in bits per second (e.g. 38400).
For more information on setting appropriate parameters, consult
the Tuning KA9Q FAQ.
-------
<flags>
-------
A number of options may be added to 'attach' commands:
'f' forces async handler to assume 16550A UART
'n' no TX flow control
If more than one flag is used, they should be concatenated. Use
of these flags is not recommended. If you do not understand the
circumstances when they should be used then you should not use
them. In particular, if you find that you need to use the 'n'
flag then you should actually be fixing your modem's
configuration so that you can use TX handshake. Otherwise,
performance will almost certainly be impaired.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Generic 'attach asy' command:
_________________________________________________________________
attach asy <ioaddress> <vector> ppp | slip <interface>
<rx_buffer_size> <mtu> <speed> [<flags>]
_________________________________________________________________
Attach a standard PC COM port, using the 8250 or 16550A chip.
_________________________________________________________________
attach asy <ioaddress> <vector> ppp <interface>
<rx_buffer_size> <mtu> <speed> [<flags>]
_________________________________________________________________
Point-to-Point-Protocol. Encapsulates datagrams in an HDLC-like
frame.
>> Example: attach asy 0x3f8 4 ppp sl0 4096 1500 38400
attach asy 0x3f8 4 ppp sl0 4096 1500 38400 fn
||
not recommended -----
_________________________________________________________________
attach asy <ioaddress> <vector> slip <interface>
<rx_buffer_size> <mtu> <speed> [<flags>]
_________________________________________________________________
Serial Line Internet Protocol. Encapsulates IP datagrams
directly in SLIP frames without a link header. This is for
operation on point-to-point lines and is compatible with 4.2BSD
UNIX SLIP.
>> Example: To attach the COM1 port to operate in point-to-point
slip mode at 9600 baud, calling it 'sl0'. A 1024-byte receiver
ring buffer is allocated. Outgoing packets larger than 256 bytes
are fragmented. RTS/CTS and carrier detection are used, together
with header compression:
attach asy 0x3f8 4 slip sl0 1024 256 9600 crv
_________________________________________________________________
attach packet <vector> <interface> <txqlen> <mtu>
_________________________________________________________________
Driver for use with separate software packet drivers meeting the
Packet Driver specification from FTP Software Inc. The driver
must have already been installed before the 'attach' command is
given.
<vector> is the software interrupt vector used for communication
to the packet driver, and <txqlen> is the maximum number of
packets that will be allowed on the transmit queue.
>> Example: In AUTOEXEC.BAT, the driver for a Western Digital
WD8003E Ethernet adapter can be installed with the command:
WD8003E 0x60 2 0x240 0xd000
This means that the adapter uses software interrupt vector 0x60,
IRQ 2, I/O address 0x240 and RAM base address 0xd000.
Then the NET packet driver can be attached to the adapter driver
with the command (in AUTOEXEC.NET):
attach packet 0x60 en0 8 1500