I have built a PCB to read the value of an analog voltage by using the
parallel port. The circuitry uses a Dual Slope A/D conversion. In
order to make that conversion, I have to count how long a certain
time-interval is. Therefore I generate a square wave of 109 kHz and try
to count that with the parallel port, this is what I do:
--> I set one bit of the parallel port, say A, high (for visualisation
on an oscilloscope)
--> then I need to count 10000 pulses, i do it with the following
C-routine:
void count(int time)
{
int value = 0;
int clock;
while (value < time) {
do
{
clock = inb(BASEPORT+1) & 0x80;
}
while (clock == 0);
do
{
clock = inb(BASEPORT+1) & 0x80;
}
while (clock == 0x80);
waarde++;
}
}
--> Then I set the bit A back to zero.
So, that means that every time i call the function count(10000) I should
always see the same HIGH-time for bit A, and that's not what happening!
The HIGH-time for A isn't a constant. I have also written a similar
program for the DOS environment and there it works just fine. My
question is: how should I solve this problem in order to have the same
HIGH-time every time i invoke the count(10000) function? How can i make
my analog voltage measurements more reliable? Is real time linux the
solution or do there exist shorter and easier ways?
I would like to mention that I'm a student and Real Time Linux is
totally new for me, so if there are easier ways to achieve my goal then
i would like to know. If Real Time Linux is the only solution for my
problem then please explain me how I should change my program or how i
should set things up.
Thanks a lot!
Bart Vandewoestyne, engineer electronics student.
--
Bart Vandewoestyne http://hello.to/MC303
Hugo Verrieststraat 48 [EMAIL PROTECTED]
8550 ZWEVEGEM ICQ# 21275340
BELGIUM - EUROPE nick: MC303
Phone: +32(0)56/75.48.11
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