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World of Ham Radio 1997
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WOHR97_AmSoft_(1997-02-01).iso
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tooslow.txt
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1997-02-01
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Machine Too Slow Message
------------------------
The Pasokon TV interface processes thousands of image samples
per second with very precise, crystal controlled, timing.
If the main processor ('486, Pentium, etc.) of your computer
doesn't handle them promptly, the image will be corrupted,
sometimes shifting the bottom of a received image to the left.
In some cases you might even get a message that the machine
is too slow. If a slow 386 works fine and a Pentium displays
a message about being too slow, there must be factors other
than the processor speed.
An MS-DOS program generally has complete control of the
computer so nothing gets in the way of this data transfer.
Usually it just works fine but there are a few things that
interfere with the precise timing required.
Memory Managers
---------------
Memory managers, such as EMM386 and QEMM, set up a virtual
machine environment for application programs. This can cause
problems for real-time applications because memory managers
add overhead to input/output instructions and interrupt
handling.
Pasokon TV version 2:
QEMM seems to add much more overhead than EMM386.
Several machines got the too slow messages with
QEMM but were fine with EMM386.
Documentation with some of the shareware SSTV
programs instruct the user to get rid of the
memory managers entirely when using that program.
Pasokon TV version 3:
This does not seem to be a problem any more. When
Pasokon TV starts up, it uses the memory manager to
obtain all the "Extended" memory then sets up its
own protected mode environment which can access
all that memory and input/output devices directly.
Mouse Movement
--------------
When you move the mouse around, it generates "interrupts"
which steal processor time from the application program.
If the time to erase the cursor and redraw it in a new
location is longer than the time to process one pixel of
an SSTV transmission, the image can get messed up.
The best solution is:
Don't move the mouse while transmitting or
receiving.
The more inquisitive might want to do some experimenting
with different interrupts. For historical reasons, the
interrupts have the following priority order:
0 (highest priority)
1
8
9
10
11
12 often bus mouse
13
14
15
3 serial port
4 serial port
5
6
7 (lowest priority)
A couple years ago, it made sense for interrupt (IRQ) 5
to be the default for Pasokon TV. This was traditionally
reserved for a second printer port (LPT2) which few
people had. More recently, the sound cards tend to use
IRQ 5 as the default. Now my recommendation is to use
10 or 11 which are generally available.
There is a tradeoff here. Interrupts 8 - 15 have slightly
more overhead due to the hardware implementation. However,
8 - 11 have a priority higher than the mouse interrupts.
Read the file IRQ.TXT for discussion of interrupts.
Device Drivers, other TSR programs
----------------------------------
An AUTOEXEC.BAT file often contains a few programs that
remain in memory and watch for a "hotkey" for perform
some other periodic function. Some of these can interfere
with the precise timing required.
There have been cases where removing a TSR program has
solved the problem.
Windows 3.1
-----------
This is not a Windows application. This is an MS-DOS
application that requires complete control of the machine for
precise timing. The best way is to completely exit out of
Windows 3.1 by picking Exit from the File menu of the
Program Manager.
It sometimes, but not always, possible to run Pasokon TV
from Windows 3.1 by running the PIF Editor and setting the
"Exclusive" attribute.
Windows 95
----------
This is a true preemptive multi-tasking operating system. What
this means is that Windows 95, not any application, is in
control of the computer. All the active applications and parts
of the operating system all take turns using the processor.
Pasokon TV will not work properly if it just gets a little
slices of time.
If you want to run Pasokon TV from Windows 95, perform these
steps after installation:
* Double click on the "My Computer" icon.
* Double click on "C:" (assuming you installed it on the
C drive).
* Double click on "PKTV3" or other directory where you
installed the software.
* Single click, with the RIGHT mouse button, on PKTV.EXE.
* Click on the tab labeled "Program".
* Click on the "Advanced..." button.
* Click on the "MSDOS mode" option, to make a check mark
mark appear in the box next to it.
* Click on "OK".
* Click on "OK".
This tells the operating system that this program requires
complete control of the computer. When you run the PKTV
program, Windows 95 will get out of the way and Pasokon TV
can transfer the image data at the required rate.
Alternatively, you could simply press the F8 key when booting
the machine and pick option 6. This will give you an MS-DOS prompt.
Disk Activity
-------------
Pasokon TV 3 uses "virtual memory". What this means is that
most of the application just pretends it has as much memory as
it wants without worrying about how much actual memory (RAM)
is available. If there isn't enough actual memory, information
is swapped to and from the disk as required.
During beta test we found out that most machines could
handle image reception while swapping images to/from disk
but a couple couldn't keep up. In the final release, this
swapping has been reduced and pretty much eliminated while
actually receving an image.
Each image requires almost one megabyte of memory, add another
megabyte for the Undo image, plus the program, clipboard,
temporary space for image scaling and other processing. Peak
usage could go has high as about 15 megabytes. If you have
16 megabytes of memory (not that uncommon based on the
registration forms!) there should be little or no swapping
to/from disk. With 8 megabytes, I'd recommend using only
5 thumbnail images at the bottom to minimize delays.
You can set this number by placing this in the PKTV.CFG file:
IMAGES 5
or by using the Setup menu.
Other Configuration File Options
--------------------------------
Use of the NO_PAUSE_CLOCK could possibly cause timing problems.
When in doubt, leave it out.
Remove any RECV_UNDO option.
First try all the other suggestions above. If you still get a
message about the machine being too slow, add this line to
the PKTV.CFG file:
SLOW_CPU
This will reduce the image sample rate for S1, S3, M1, and M3
transmission modes which are the most demanding. The image
quality will be reduced slightly.