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AP_RPM: define a minimum acceptable period for PWM input

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this will reject very short periods as invalid. This helps somewhat
with noise on the line
This commit is contained in:
Andrew Tridgell 2015-08-08 19:08:43 +10:00 committed by Randy Mackay
parent cb423eb2f4
commit 90d760f50e
1 changed files with 7 additions and 1 deletions
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8
libraries/AP_RPM/RPM_PX4_PWM.cpp
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@ -34,6 +34,12 @@
extern const AP_HAL::HAL& hal; extern const AP_HAL::HAL& hal;
/*
don't accept periods below 100us as it is probably ringing of the
signal. It would represent 600k RPM
*/
#define RPM_MIN_PERIOD_US 100
/* /*
open the sensor in constructor open the sensor in constructor
*/ */
@ -79,7 +85,7 @@ void AP_RPM_PX4_PWM::update(void)
while (::read(_fd, &pwm, sizeof(pwm)) == sizeof(pwm)) { while (::read(_fd, &pwm, sizeof(pwm)) == sizeof(pwm)) {
// the px4 pwm_input driver reports the period in microseconds // the px4 pwm_input driver reports the period in microseconds
if (pwm.period > 0) { if (pwm.period > RPM_MIN_PERIOD_US) {
sum += (1.0e6f * 60) / pwm.period; sum += (1.0e6f * 60) / pwm.period;
count++; count++;
} }