Configuration: +Timer Constants

The timing constants are defined near the beginning of the template port +implementation of the platform specific layer in ...\template\template_variant\specific\xyin.cpp.

The values and their meaning are as follows:

KInterSampleTime

This +constant determines the rate at which individual samples within a group are +collected.

A group of samples is collected when the pen is down, and, +in the template port, this is handled by DTemplateDigitiser::TakeSample().

Once +all the samples in a group have been collected, the function calls Digitiser::RawSampleValid() in +the platform independent layer, whose main purpose is to ensure the validity +of the samples by checking the spread. If the samples appear valid, it averages +the samples to obtain the current position.

The setting of the timer +constant depends on the sample resolution of the digitizer:

A high resolution can +lead to more jitter between samples, and therefore more smoothing is required +to obtain nice steady values. This argues for higher sampling rates, and a +smaller value of KInterSampleTime.
A low resolution means +that there is very little variation between consecutive samples, and therefore +fewer are required. This argues for lower sampling rates, and a larger value +of KInterSampleTime.

Another consideration when setting this constant is the speed of +the communications between the MPU and the digitizer.

In the Symbian +reference ports, this value varies between 1 and 3.

KPenDownDelayTime

This +value is used in the implementation of the pen +interrupt interrupt service routine (ISR). It represents a delay, measured +in nano-kernel ticks, between a pen down event and the start of the collection +of digitizer samples.

The value is optional. Choose a value of 0 if +no delay is required. Typically, a value of 2 is chosen.

KInterGroupTime

This +value is used in DTemplateDigitiser::WaitForPenUp() and DTemplateDigitiser::WaitForPenUpDebounce(). +After a group of samples has been collected, there is a delay, dictated by +the value of this constant, before the collection for the next group begins.

The +inverse of the sum of KInterSampleTime, +and KInterGroupTime will therefore determine the frequency +at which groups of samples are taken. This, in turn, dictates how often pen +movement events are issued, and, if no interrupt is used on pen up, how quickly +this situation is ascertained. The constant is optional. Typically it is set +at 1ms

The delay is optional, a value of zero meaning that there is +no delay. Typically, a value of 1 is chosen.

KPenUpDebounceTime

This +value is used in DTemplateDigitiser::TakeSample(). If, during +sample collection, the pen goes up, then the digitizer will wait for this +period of time before deciding whether the removal of the pen is momentary, +or whether it is an intentional removal - this is also referred to as debounce.

If, +after the delay, the pen is still up, then a pen-up event is issued; otherwise +the state of the digitizer reverts to collecting mode, resetting the sample +buffer

Typically, this value is set to around 30.

KPenUpPollTime

This +value is used in DTemplateDigitiser::TakeSample().

If +the pen is down when the system powers on, then the digitizer is sampled using +this delay until the pen is up.

Typically, this value is set at 30.