dlc wrote:
I have an odd problem and I'm hoping that by trying to explain it I can
solve it...
What I have is an timer overflow ISR that tics off every 10us. I've
coded it thusly:
// variables at the top (global)
//ISR variables, volatile by nature
volatile uint16_t t_10us=0;
volatile uint32_t t_1ms=0;
volatile uint16_t repeat=0;
volatile uint16_t match=0; // The single servo used
uint8_t servo = 150;
// past initializations and such ...
SIGNAL(SIG_OUTPUT_COMPARE0)
/*
* 10 microsecond ISR
*/
{
t_10us++;
if (t_10us > 100)
{
t_1ms++; //1ms background clock
t_10us = 0;
repeat++;
if (repeat == 19)
{
repeat = 0;
SPIN = 1; //raise servo pin high
match = 0; //start servo timer
}
}
match++; //increment every 1
if (match == servo)
SPIN=0; //drop servo bit
}
You really should just use the output compares to do timed pulses,
instead of wasting all your cpu power just doing this.
Anyway, you problem is that you're updating servo in the main loop while
updating match in the interrupt, so chances are they are running paste
each other...
The proper way to write that code (apart from using output compares)
would be something like:
volatile uint16_t next_pulse;
SIGNAL(SIG_OUTPUT_COMPARE0)
{
match++; // increment every 1
if (match > next_pulse)
SPIN = 0; // drop servo bit
else
SPIN = 1; // raise servo pin high
if (match >= 20000) {
next_pulse = servo;
match = 0; //start servo timer
}
}
I hope this helps,
--
Paulo Marques
Software Development Department - Grupo PIE, S.A.
Phone: +351 252 290600, Fax: +351 252 290601
Web: www.grupopie.com
"Prediction is hard. Especially of the future."
Niels Bohr
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