home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Tech Arsenal 1
/
Tech Arsenal (Arsenal Computer).ISO
/
tek-05
/
cheaplnk.zip
/
CHEAPLNK.DOC
< prev
next >
Wrap
Text File
|
1989-12-22
|
7KB
|
149 lines
CHEAPLINK - V1.11 - 27 Apr 89 -- Zero slot Network written by EM - Hong Kong
Performance: 18 s to transfer 64k.
Installation:
On the Server:
in Autoexec.bat: SRV $nn1/dd1 [$nn2/dd2...] [UNITS:abc...]
On each Workstation:
in Config.sys: DEVICE = WKS $nnn/ddd @n
Notes:
nnx = port base address in DECIMAL notation (COM1 = 1016; COM2 = 760).
ddx = baud rate divisor (1 = 115,200 bps; 2 = 57,600 bps...).
abc... = disk units on the server made available to the workstations
(omitting this option implies "all").
n = number of available server drives accessed by the workstation.
*- example srv $1016/1 efg
*- device = wks.sys $1016/1 @3
*-
*- selects com1 on both machines
*- maximum baudrate
*- drives A: B: and C: on server become E: F: and G: on wkstation
*- workstation accesses 3 drives
*-
No interrupts are used on the I/O ports.
The serial cable is a limited EIA (3-wires) null modem (rx to tx, tx to rx,
ground to ground).
for 25 pin connectors: tx = pin 2; rx = pin 3, ground = pin 7;
for 9 pin connectors: tx = pin 3; rx = pin 2, ground = pin 5).
The server may handle up to 15 satellite workstations, connected to
different serial ports.
The server driver is a TSR utility working in background; yet, it eats up
only less than 5 kbytes.
The LPT1 of every satellite workstation is redirected on the server's LPT1;
the other printers are unaffected.
Technical details:
The satellite workstation software driver (wks.sys) reroutes all the
requests to the remote server, via a serial line up to 115,200 bps.
The server driver SRV.COM is activated by a numer of interrupts: namely,
Dos Idle (28h), Timer Tick (08h), Hw Keyboard (09h) and Keyboard Bios
Services (16h). It also hooks to the Disk Bios Services (13h), but only
to set a flag when the foreground programs are acceding to the disks
(the local disk I/O is achieved through direct FAR calls to the local
block device drivers).
Every time someone (server or workstations) do any write on a shared unit,
a system of flags is set to signal that the disk content has changed and
the buffers should be flushed. For this purpose, the device driver returns
a "maybe media has changed" status. That's easy on the workstation; on
the server it has required wild patches in the DOS, automatically
operated by SRV.COM during the installation (shortly, SRV replaces the
existing device drivers patching every reference to their far address
found between 70:0 and 70:ffff. With DOS 3.30 it seems to work, but I'm not
sure what's going to happen in the future releases. Unfortunately, to
insert the modified driver in the linked list isn't enough, because
the DOS also copies the block device driver addresses in undocumented
places).
As no serial input interrupts are used, the only way to protect against
overrun errors is to wait, after every character output, for an acknowledge
from the other side (in form of plain echo). That's done from both the
sides of the serial link. The bad new is, this degrades the performances
by a factor of at least two (but... a la guerre comme a la guerre).
In return, the communication is very safe, being protected by a
triple mechanism: (odd) parity, echo and checksum on block transfers. This
is of paramount importance, as bad data transfers could disrupt the disk
structures and perhaps trash the disk.
Any communication error results in a disk error message on the workstation
(followed by the notorious "Abort, Retry, Fail?" or equivalent). As far
as I know, a "R"etry always successfully recovers the operations - provided
that the error was oly temporary, of course: no "R"etry will push the bits
over a cut in the cable!
As TSR, SRV.COM is very well-behaved, but possibly some foreground applications
are not. For example, Framework III makes a mess slowing the tick rate
down to 1 per second, and never uses INT 16h (it plays directly with the
keyboard buffer instead). That means that if the server is running that
application, some activities such as the nework printing are greatly slowed
down. Unidentified troubles also arise when the server runs MS-Windows.
Many tricks have been used to overcome the non-reentrancy of
DOS and BIOS code. As far as I know, under normal conditions the system
never crashes.
Credits:
This program is based on Weaklink, a shareware product from Don Jindra
(Information Modes).
Some ideas came from the host of commercially available zero-slot LAN's
(such LanLink, Laplink, Brooklin Bridge etc.)
Have fun -- EM
----------------end-of-author's-documentation---------------
Software Library Information:
This disk copy provided as a service of
Public (software) Library
We are not the authors of this program, nor are we associated
with the author in any way other than as a distributor of the
program in accordance with the author's terms of distribution.
Please direct shareware payments and specific questions about
this program to the author of the program, whose name appears
elsewhere in this documentation. If you have trouble getting
in touch with the author, we will do whatever we can to help
you with your questions. All programs have been tested and do
run. To report problems, please use the form that is in the
file PROBLEM.DOC on many of our disks or in other written for-
mat with screen printouts, if possible. PsL cannot debug pro-
programs over the telephone, though we can answer questions.
Disks in the PsL are updated monthly, so if you did not get
this disk directly from the PsL, you should be aware that the
files in this set may no longer be the current versions. Also,
if you got this disk from another vendor and are having prob-
lems, be aware that some files may have become corrupted or
lost by that vendor. Get a current, working disk from PsL.
For a copy of the latest monthly software library newsletter
and a list of the 3,000+ disks in the library, call or write
Public (software) Library
P.O.Box 35705 - F
Houston, TX 77235-5705
Orders only:
1-800-2424-PSL
MC/Visa/AmEx/Discover
Outside of U.S. or in Texas
or for general information,
Call 1-713-524-6394
PsL also has an outstanding
catalog for the Macintosh.