Hi! > +Challenges > + > +One of the difficulties in implementing a generic PWM framework is the > +fact that pulse-width-modulation applications involve real-world > +signals, which often must be carefully managed to prevent destruction > +of hardware that is linked to those signals. A DC motor that > +experiences a brief interruption in the PWM signal controlling it > +might destructively overheat; it could suddenly change speed, losing > +synchronization with a sensor; it could even suddenly change direction > +or torque, breaking the mechanical device connected to it.
Stop right here. Linux is not hard realtime os, nor is it an os that never crashes. > +(A generic PWM device framework is not directly responsible for > +preventing the above scenarios: that responsibility lies with the > +hardware designer, and the application and driver authors. But it Exactly; if your hw can be damaged by software, it was misdesigned. Is the paragraph #1 really neccessary? > +Using the API to Generate PWM Signals -- Basic Functions for Users > + > + > +pwm_request() -- Returns a pwm_channel pointer, which is subsequently > +passed to the other user-related PWM functions. Once requested, a PWM > +channel is marked as in-use and subsequent requests prior to > +pwm_free() will fail. > + > +The names used to refer to PWM devices are defined by driver authors. > +Typically they are platform device bus identifiers, and this > +convention is encouraged for consistency. > + > + > +pwm_free() -- Marks a PWM channel as no longer in use. The PWM device > +is stopped before it is released by the API. free is normally used for something else. Rename to open/close? > +pwm_start(), pwm_stop() -- Turns the PWM signal on and off. Except > +where stated otherwise by a driver author, signals are stopped at the > +end of the current period, at which time the output is set to its > +inactive state. What does it mean to stop a signal? What is the difference between 0% duty cycle and stop() ? > +pwm_polarity() -- Defines whether the PWM signal output's active > +region is "1" or "0". A 10% duty-cycle, polarity=1 signal will > +conventionally be at 5V (or 3.3V, or 1000V, or whatever the platform > +hardware does) for 10% of the period. The same configuration of a > +polarity=0 signal will be at 5V (or 3.3V, or ...) for 90% of the > +period. Is polarity realy required? Can't driver just replace duty with 100%-duty? -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
