This is a brief note regarding a windows timing issue that bit me when
I wrote the WSE control program for windows. I am hoping my posting it
will save someone from hours wasted.
In the WSE control program I wrote, it was necessary for me to insert a
'sleep'
statement after I wrote each bit to the printer, or the printer commands
would not properly control the WSE units. Sleep(1) was sufficient for
this purpose.
When I ran the WSE controller in the Delphi IDE the speed of my Up/Down-arrow
routine for setting frequency was good and I could move from one end of
the band to the other in a second or two.
But when running the executable file directly from Windows XP64,
sometimes the speed was great and other times it was 10-20 times
slower! There seemed to be no rhyme or reason to this, and it was not
CPU-use-related, as the CPU use was on the order of 5% or less.
My first WSE controller code had been just a quick hack to get things
working, so after this problem surfaced I optimized the code as best I
could, through several iterations, figuring that improving the
efficiency of the code would resolve the problem. After each iteration
of code improvement the controller was quite fast and I was convinced I
had fixed things. Then later the speed would again drop to a snail's
pace. I was surfing the web and running various other applications
throughout this process.
It turns out that the default windows timer, on which the sleep
function depends, does not function as one might think. The function
parameter () is used to set the sleep time in increments of 1 msec,
down to a minimum of 1 msec [e.g. sleep(1)]. But in its default state,
the timer interval/resolution actually doesn't go below 15 ms. If you
set it to any number between 1 and 15 it will be [approximately] 15
msec. But you can set the timer to 'high resolution' using the Windows
Multimedia function timeBeginPeriod() where the resolution is specified
in milliseconds, with a minumum of 1 msec. When you no longer need the
high resolution timer, you then revert to the default timer by using
timeEndPeriod() and specifying the same resolution.
What happened to me is that when I entered the Delphi IDE it set the
timer to high resolution and so my program ran quickly. When I closed
the IDE the default timer was returned to standard resolution, so
things slowed down. But at times other other applications I was
running [and some of the webpages I was surfing] were resetting the
timer resolution to high resolution, and thus affecting my program's
speed, and making me think that I had 'fixed' the problem. Then going
to another webpage or changing the mix of applications that was open
would reset the timer to its original low-resolution state! Although
some documents suggest that the timeBeginPeriod and timeEndPeriod
functions are application-specific, they are NOT so, and affect the
performance of other applications that are running under Windows at the
same time, as my experience showed.
If you are using a sleep command in windows or another function that
depends on the resolution of the windows timer, I would suggest that
you explicitly set the timer resolution using timeBeginPeriod() before
you use the sleep function [or any other function that depends on the
default windows timer], and then reset it to default at termination
using timeEndPeriod().
There is a nice free, downloadable application that lets you see what
your default windows timer is doing at:
http://www.grahamwideman.com/gw/tech/dataacq/skedgran/skedgran.htm
There is a nice story of how surfing the Yahoo Finance page can appear
to improve your computer's performance by this mechanism at:
http://www.codeproject.com/tips/YahooSpeeds.asp
You don't need to download the application from the Yahoo Finance story
page to check this out; just use the SkedGran application from the
first URL I gave and check the default timer result, then open the
Yahoo Finance page, recheck it, and then close the Yahoo page and check
it again.
My love for Windows continues to grow...NOT!
73,
W3SZ
Roger Rehr
http://www.nitehawk.com/w3sz
Roger Rehr
W3SZ
http://www.nitehawk.com/w3sz
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