nn::hid::CTR::AccelerometerReader Class

class AccelerometerReader : private nn::util::NonCopyable< AccelerometerReader >

Class for loading sampling data from the accelerometer.

Sampling Rate

The accelerometer starts sampling when the first instance is generated, sampling data at intervals of roughly 10 milliseconds. Sampling stops when no instances exist.
If you want to monitor the exact timing of sampling, you can use the Accelerometer class to know precisely when sampling occurs.

No sampling is done right after generating a class instance or right after recovering from sleep, so there are times when the Read and ReadLatest functions do not get valid results. Waiting until results have been sampled at least once avoids this situation, so Nintendo recommends calling the nn::hid::CTR::HidBase::WaitSampling function of the nn::hid::CTR::Accelerometer class right after generating a class instance or when recovering from sleep. This wait time is the same as the sampling frequency, up to a maximum of approximately 10 milliseconds.

Generating/Destroying Instances and Sampling Processes

As mentioned, the generation/destruction of instances is linked to the switching of sampling processes. Because the switching of sampling processes puts a load on the system, you should try to use the same instance while using the accelerometer and otherwise refrain from frequent generation and destruction of instances.
Below is an example of what you should avoid.

   void GetAccelerometerValue(f32* x,f32* y,f32* z)
   {
      AccelerometerReader reader;	// Generate instance: Start of sampling
      AccelerometerStatus status;

      reader.ReadLatest( &status );     // Get value
      *x = status.speed.x;
      *y = status.speed.y;
      *z = status.speed.z;
      
      return;                   // Destroy reader: Sampling stops
   }
   
   void MainLoop() // Loop called once per frame
   {
       ... some sort of processing .....
       GetAccelerometerValue( &x, &y, &z );  // Value obtained once in every frame
       
       ... some sort of processing .....
   }
   

In the example above, an instance of AccelerometerReader is created and destroyed on the stack in every frame. Because the process does not wait the minimal time for sampling by the accelerometer, in some cases appropriate values are not obtained. This is a bad design. The design should be revised, for example, by creating the instance in the heap, so that the instance continues to exist throughout the interval during which the application needs to get the acceleration.

Output Value Processing Features

This class includes the following features to process output values.

Acceleration Variation Tolerance	You can apply a correction to control any major variation in acceleration during continuous sampling.
Offset Correction	Outputs after subtracting the specified value from sampling results.
Axial Rotation	Outputs sampling results multiplied by an optional rotation matrix. Enables the output of values as if the accelerometer is on an incline.

All processing features are disabled by default. Configure and enable them as needed. For details, see the various function references.

Axis Orientation

The default accelerometer sensors are as follows.

X+	The direction indicated by Left on the +Control Pad
Y+	The direction normal to and outward from the Touch Screen
Z+	The direction indicated by Up on the +Control Pad

Recalibration from the HOME Menu

Effective from the first network update, the HOME Menu has a feature enabling users to recalibrate the accelerometer whenever they like.

Thus, in some cases, correction of the accelerometer in accordance with the user's environment may take place while the system is transitioning from the application to the HOME Menu upon pressing the HOME Button.
After this operation, the values obtained by the Read and ReadLatest functions are the corrected values. In most cases, the corrected values accurately reflect the user's environment.

The applications, however, need not take any special measures to deal with this.

nn::util::NonCopyable
  nn::hid::CTR::AccelerometerReader

2012/01/12

Corrected the indication that frequent generation/destruction of instances was prohibited.
Updated the text about recalibration from the HOME Menu.
Restructured the description about the timing of the start of sampling.

2011/10/06

Noted you may not be able to get values using the example of what not to do.

2011/08/30

Added text about creation and destruction of instances.

2011/03/15

Added note about the possibility of recalibration from the HOME menu.

2010/12/06

Added explanation of conditions under which sampling stops.

2010/01/07

Initial version.