diff options
Diffstat (limited to 'wirish/HardwareTimer.h')
| -rw-r--r-- | wirish/HardwareTimer.h | 285 |
1 files changed, 274 insertions, 11 deletions
diff --git a/wirish/HardwareTimer.h b/wirish/HardwareTimer.h index c6e11c8..b05085f 100644 --- a/wirish/HardwareTimer.h +++ b/wirish/HardwareTimer.h @@ -29,6 +29,26 @@ #ifndef _TIMER_H_ #define _TIMER_H_ +/** + * Interface to one of the 16-bit timer peripherals. + * + * User code should not instantiate this class directly; instead, use + * one of the predefined Timer<n> instances (Timer1, Timer2, etc.). + * + * HardwareTimer instances can be configured to generate periodic or + * delayed events with minimal work done by the microcontroller. Each + * timer maintains a single 16-bit count that can be configured with a + * prescaler and overflow value. + * + * By default, a timer's counter is incremented once per clock cycle. + * The prescaler acts as a divider of the 72MHz Maple system clock; + * without prescaling, the timer's count would reach 65535 (2**16-1) + * and roll over over 1000 times per second. + * + * The overflow value is the maximum value the counter will reach. It + * defaults to 65535; smaller values will cause the counter to reset + * more frequently. + */ class HardwareTimer { private: uint16 overflow; @@ -37,39 +57,282 @@ class HardwareTimer { public: HardwareTimer(uint8 timer_num); + /** + * Stop the counter, without affecting its configuration. + * + * The timer will no longer count or fire interrupts after this + * function is called, until it is resumed. This function is + * useful during timer setup periods, in order to prevent + * interrupts from firing before the timer is fully configured. + * + * Note that there is some function call overhead associated with + * this method, so using it in concert with + * HardwareTimer::resume() is not a robust way to align multiple + * timers to the same count value. + * + * @see HardwareTimer::resume() + */ void pause(void); + + /** + * Resume a paused timer, without affecting its configuration. + * + * The timer will resume counting and firing interrupts as + * appropriate. + * + * Note that there is some function call overhead associated with + * using this method, so using it in concert with + * HardwareTimer::resume() is not a robust way to align multiple + * timers to the same count value. + * + * @see HardwareTimer::pause() + */ void resume(void); + + /** + * Set the timer prescale. + * + * The prescaler acts as a clock divider to slow down the rate at + * which the counter increments. + * + * For example, the system clock rate is 72MHz, so the counter + * will reach 65535 in (13.89 nanoseconds) * (65535 counts) = + * (910.22 microseconds), or about a thousand times a second. If + * the prescaler equals 1098, then the clock rate is effectively + * 65.56KHz, and the counter will reach 65536 in (15.25 + * microseconds) * (65536 counts) = (0.999 seconds), or about once + * per second. + * + * The HardwareTimer::setPeriod() method may also be used as a + * convenient alternative. + * + * @param factor The new prescale value to set. + * @see HardwareTimer::setPeriod() + */ void setPrescaleFactor(uint16 factor); - void setOverflow(uint16 val); // truncates to overflow - void setCount(uint16 val); // truncates to overflow + + /** + * Sets the timer overflow (or "reload") value. + * + * When the timer's counter reaches this, value it resets to + * zero. Its default value is 65535 (the largest unsigned 16-bit + * integer); setting the overflow to anything lower will cause + * interrupts to be called more frequently (see the setPeriod() + * function below for a shortcut). This number sets the maximum + * value for the channel compare values. + * + * @param val The new overflow value to set + * @see HardwareTimer::setOverflow() + */ + void setOverflow(uint16 val); + + /** + * Set the current timer count. + * + * Note that there is some function call overhead associated with + * callign this method, so using it is not a robust way to get + * multiple timers to share a count value. + * + * @param val The new count value to set. If this value exceeds + * the timer's overflow value, it is truncated to the + * overflow value. + */ + void setCount(uint16 val); + + /** + * Retrieve the current timer count. + * + * @return The timer's current count value + */ uint16 getCount(void); - // tries to set prescaler and overflow wisely; returns overflow + /** + * Configure the prescaler and overflow values to generate a timer + * reload with a period as close to the given number of + * microseconds as possible. + * + * The return value is the overflow, which may be used to set + * channel compare values. However, if a clock that fires an + * interrupt every given number of microseconds is all that is + * desired, and the relative "phases" are unimportant, channel + * compare values may all be set to 1. + * + * @param microseconds the desired period of the timer. + * @return the overflow value (and thus, the largest value that can be + * set as a compare). + */ uint16 setPeriod(uint32 microseconds); - void setChannel1Mode(uint8 mode); - void setChannel2Mode(uint8 mode); - void setChannel3Mode(uint8 mode); - void setChannel4Mode(uint8 mode); - void setCompare1(uint16 val); // truncates to overflow - void setCompare2(uint16 val); // truncates to overflow - void setCompare3(uint16 val); // truncates to overflow - void setCompare4(uint16 val); // truncates to overflow + + /** + * Set channel 1 of this timer to the given mode. + * + * Note: Timer1.setChannel1Mode(TIMER_PWM) may not work as + * expected; if you want PWM functionality on a channel make sure + * you don't set it to something else! + * + * @see TimerMode + */ + void setChannel1Mode(TimerMode mode); + + /** + * Set channel 2 of this timer to the given mode. + * @see TimerMode + */ + void setChannel2Mode(TimerMode mode); + + /** + * Set channel 3 of this timer to the given mode. + * @see TimerMode + */ + void setChannel3Mode(TimerMode mode); + + /** + * Set channel 4 of this timer to the given mode. + * @see TimerMode + */ + void setChannel4Mode(TimerMode mode); + + /** + * Sets the compare value for channel 1. + * + * When the counter reaches this value the interrupt for this + * channel will fire if channel 1 mode is TIMER_OUTPUTCOMPARE and + * an interrupt is attached. + * + * By default, this only changes the relative offsets between + * events on a single timer ("phase"); they don't control the + * frequency with which they occur. However, a common trick is to + * increment the compare value manually in the interrupt handler + * so that the event will fire again after the increment + * period. There can be a different increment value for each + * channel, so this trick allows events to be programmed at 4 + * different rates on a single timer. Note that function call + * overheads mean that the smallest increment rate is at least a + * few microseconds. + * + * @param val The compare value to set. If greater than this + * timer's overflow value, it will be truncated to the + * overflow value. + * + * @see TimerMode + * @see HardwareTimer::setChannel1Mode() + */ + void setCompare1(uint16 val); + + /** + * Sets the compare value for channel 2. + * + * @param val The compare value to set. If greater than this + * timer's overflow value, it will be truncated to the + * overflow value. + * @see HardwareTimer::setCompare1() + */ + void setCompare2(uint16 val); + + /** + * Sets the compare value for channel 3. + * + * @param val The compare value to set. If greater than this + * timer's overflow value, it will be truncated to the + * overflow value. + * @see HardwareTimer::setCompare1() + */ + void setCompare3(uint16 val); + + /** + * Sets the compare value for channel 4. + * + * @param val The compare value to set. If greater than this + * timer's overflow value, it will be truncated to the + * overflow value. + * @see HardwareTimer::setCompare1() + */ + void setCompare4(uint16 val); + + /** + * Attach an interrupt handler to this timer's channel 1. This + * interrupt handler will be called when the timer's counter + * reaches its channel 1 compare value. + * + * The argument should be a function which takes no arguments and + * has no return value; i.e. it should have signature + * + * void (*handler)(void); + * + * Note: The function (often called an interrupt service routine, + * or ISR) should attempt to return as quickly as possible. + * Blinking the LED, some logic, PWM updates, and Serial writes + * are fine; writing to SerialUSB or waiting for user input can + * take a long time and other compare interrupts won't fire. Tip: + * if you have a delay() in your interrupt routine, you're probably + * doing it wrong. + * + * @param handler The ISR to attach to channel 1. + * @see voidFuncPtr + */ void attachCompare1Interrupt(voidFuncPtr handler); + + /** + * Like attachCompare1Interrupt(), but for channel 2. + * @see HardwareTimer::attachCompare1Interrupt() + */ void attachCompare2Interrupt(voidFuncPtr handler); + + /** + * Like attachCompare1Interrupt(), but for channel 3. + * @see HardwareTimer::attachCompare1Interrupt() + */ void attachCompare3Interrupt(voidFuncPtr handler); + + /** + * Like attachCompare1Interrupt(), but for channel 4. + * @see HardwareTimer::attachCompare1Interrupt() + */ void attachCompare4Interrupt(voidFuncPtr handler); + + /** + * Remove the interrupt handler attached to channel 1, if any. + * The handler will no longer be called by this timer. + * @see HardwareTimer::attachCompare1Interrupt() + */ void detachCompare1Interrupt(void); + + /** + * Remove the interrupt handler attached to channel 2, if any. + * The handler will no longer be called by this timer. + * @see HardwareTimer::attachCompare1Interrupt() + */ void detachCompare2Interrupt(void); + + /** + * Remove the interrupt handler attached to channel 3, if any. + * The handler will no longer be called by this timer. + * @see HardwareTimer::attachCompare1Interrupt() + */ void detachCompare3Interrupt(void); + + /** + * Remove the interrupt handler attached to channel 4, if any. + * The handler will no longer be called by this timer. + * @see HardwareTimer::attachCompare1Interrupt() + */ void detachCompare4Interrupt(void); }; +/** Pre-instantiated timer for use by user code. */ extern HardwareTimer Timer1; +/** Pre-instantiated timer for use by user code. */ extern HardwareTimer Timer2; +/** Pre-instantiated timer for use by user code. */ extern HardwareTimer Timer3; +/** Pre-instantiated timer for use by user code. */ extern HardwareTimer Timer4; #if NR_TIMERS >= 8 +/** Pre-instantiated timer for use by user code, on devices with + more than four timers (this does not include the Maple). */ extern HardwareTimer Timer5; +/** Pre-instantiated timer for use by user code, on devices with + more than four timers (this does not include the Maple). */ extern HardwareTimer Timer8; #endif |