Incompatible with PWM output in some instances

[unforgiven512]

Due to this implementation's use of the SparkIntervalTimer library, in certain instances, this can cause PWM functionality to become inoperable on certain groups of pins on the Photon (NOTE: this may be true for other Particle devices, as well; I only have a Photon for testing), depending on which hardware timer is allocated to the timer_isr() function at the time of instantiation.

When the timer_isr() function is instantiated, the "dynamic timer allocation" feature will cause the timer to use interrupts generated by one of the following timers on the Photon:

• TIM3
• TIM4
• TIM5
• TIM6
• TIM7

Now, this is all and well, however, the Photon uses the timers TIM3, TIM4, and TIM5 for the generation of PWM signals on various pins:

PIN	TIMER	NOTES
D0	TIM4
D1	TIM4
D2	TIM3
D3	TIM3
A4	TIM3
A5	TIM3
WKP	TIM5

Timer TIM6 and TIM7 are not (directly) connected to any I/O pins on the Photon, so it would be preferential to use these two timers by directly specifiying one of the two during the instantiation of the IntervalTimer object.

However, as both this library (IRRemote) and the SparkIntervalTimer library support both the Core and Photon as target platforms, it would not be wise to simply assume that TIM6 or TIM7 is available.

The Core has TIM2, TIM3, and TIM4 available, all of which as associated with PWM output pins, so at least some of the PWM functionality will be lost. Unfortunately, my Core is no longer working (the CC3000 WiFi module has failed solder connections, causing the device to remain in an unbootable state), so I am unable to perform any testing for this target.

Platform detection can be performed via conditional preprocessor directives:

#if defined(STM32F10X_MD) || !defined(PLATFORM_ID)
#define PIO_PLATFORM_CORE
#elif defined(STM32F2XX) && defined(PLATFORM_ID)
#define PIO_PLATFORM_PHOTON
#else
#error "--- ERROR: Device is not supported by this library. Only Particle Core and Particle Photon are supported. ---"
#endif /* <PLATFORM DETECTION> */

An ideal solution may be to allow the user to specify their preferred timer (in any case), use automatic allocation on the Core target, and (if not explicitly selected), use either TIM6 or TIM7 on the Photon target. I am currently unsure if TIM6 or TIM7 are used elsewhere; if they are used elsewhere, it may be ideal to select one based on some type of "priority" scheme.