Hello=20

I'm a student in computer science in Belgium and it is my last year of st=
udy.=20
My thesis consists in realising an automatic horizon for a camera which=20
is in a remotily controled helicopter (www.flying-cam.com).=20

I studied Intel assembly at school, but I've never learned how to=20
program a microcontroler. So I looked for help and tutorials on the=20
Internet. I'm working with PIC's since only two months.=20

I'm currently coding my automatic horizon software on a PIC16F877=20
and I have some real time problems. I'll try explain that clearly.=20

My PIC must measure a PWM signal in input, then it computes this value=20
with values from captors (accelerometer and gyro), finaly it outputs the=20
result in the form of an other PWM signal.=20

I must measure the input signal with 1 =B5s precision.=20
I use the RBIF interrupt to detect the edges of the input signal,=20
timer 0 to measure the lenght of the signal. I use timer 1 with the CPP=20
to output the result signal.=20
TMR2 is used to generate the frequency of the output=20
signal. The problem is that RBI interrupt can occur while=20
executing the tmr2 interrupt code, and the measure of=20
the input signal will be faulty because the RBI does not=20
react immediately. So I've used nested=20
interrupts with a software stack (I found this method in the piclist=20
source code library), but there is always a=20
part of the code where interrupts are disabled.=20

[Update] I use the two CPP to output signals. These signals are used
to make spinning a motor. The motor have to spin in the two ways,
so when the motor have to spin left, I use CPP1, and when it have to
spin right, I use CPP2

Does anybody has an idea to make this measure accurately ?=20

Thanks a lot for your help.=20


Laurent=20

NB : I'm french speaking, so I hope I haven't made too=20
much mistakes in English=20

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