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MCUdude / MegaCoreX

An Arduino hardware package for ATmega4809, ATmega4808, ATmega3209, ATmega3208, ATmega1609, ATmega1608, ATmega809 and ATmega808
GNU Lesser General Public License v2.1
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Servo Library framerate bug #73

Closed KHeintz closed 3 years ago

KHeintz commented 4 years ago

Somewhere there is a bug in the Servo Library of MegaCorex. The framerate of 4ms is much too short and kills every analog servo. REFRESH_INTERVAL has no effect. If I use the original servo library the framerate is correct. To use it you only have to add the timer TCB3 to the servo timer and to the servo.cpp. Illustrated with an ATMega4809 40 Pin and the Knob example. Change to the Arduino servo library megaavr Servo Timer.h add

if defined(SERVO_USE_TIMERB3)

&TCB3;

endif

Servo.cpp add

elif defined(SERVO_USE_TIMERB3)

ISR(TCB3_INT_vect)

MegaCorex Orginal

SpenceKonde commented 4 years ago

Posting on here so I get notifications - and to ask a few questions.

This is really my problem to deal with, not @MCUdude's - his implementation of Servo is a direct copy of what I did for megaTinyCore in order to remove Servo's dependence on the prescaler of TCA0 (which is the sort of insane stupidity that makes you want to reach through the screen and slap the Arduino team for - right up there with making TCB-for-millis depend on the TCA0 prescaler too, when you can rig up TCB0 as millis so an overflow happens exactly once per ms, and then just rightshift the TCB count in micros - reconfiguring TCA0 to get custom speed PWM is not a particularly exotic thing to want to do...)

Can you explain a bit more what the constraints are here, w/regards to how often the signal is sent? What is the minimum refresh interval? What is the maximum?

Also, what do you mean by "analog servo"? I did my testing with one of the ubiquitous MG90S servos from ebay. Do those tolerate some sorts of input that your "analog servos" do not?

KHeintz commented 4 years ago

The problem is the refresh interval (frame time) does not work in this Servo Library. The electronics of servos can be digital or analog. Accordingly, servos are classified as digital or analog servos. Digital servos have a higher angular resolution and the servo position is controlled faster and more precisely. The pulse width for both servo types is in the normal range between 1ms and 2ms. A servo pulse of 1.5 ms width will typically set the servo to its "neutral" position (typically half of the specified full range), a pulse of 1 ms will set it to 0°, and a pulse of 2.00 ms to 90° (for a 90° servo). Frame times (refresh_interval) for analog servos are around ~20ms. 18-22ms are normal, all under 16ms are much to short. This is the "standard pulse servo mode" used by all analog servos. Longer frame times are not a problem. Much shorter frame times cause extreme power consumption and overheating. In addition, the servos can twitch uncontrollably or lose their neutral point or stop operation immediately. Anlog https://de.wikipedia.org/wiki/Servo#/media/Datei:TiemposServo.svg

KHeintz commented 4 years ago

MG90S is a digital servo and the short frame time does not matter. Do the test with a HXT900 for example and soon it will be clear what I mean.

MCUdude commented 3 years ago

Fixed in c2321a7