joystick.c File Reference

Analog joystick input. More...

#include "joystick.h"

Go to the source code of this file.

Functions
void	joystick_init (void)
	Initialize joystick state and peripherals. More...
struct joystick_vect	joystick_get_pos (void)
	Get most recent recorded joystick direction. More...
bool	joystick_pushed (void)
	Whether the joystick button is pressed. More...

Detailed Description

Analog joystick input.

Author

Istvan Burbank, Peter Friend, James Cassell

Date

2016-11-10 This module has no state kept in C because the ADC runs continuously as fast as possible and when the module is polled it just polls the ADC registers.

Definition in file joystick.c.

Function Documentation

joystick_get_pos()

struct joystick_vect joystick_get_pos

(

void

)

Get most recent recorded joystick direction.

The ADC is constantly converting, this returns the most recently sampled vector of the joystick position. This should be polled as frequently as desired, there is no notion of "consuming" a value.

Definition at line 111 of file joystick.c.

                                            {
  // the ADC is a 10 bit output, and we ask for it in "Integer 16 bit", which is
  // implicitly unsigned (see family reference manual register 17-1).

  // these won't overflow because the ADC value is only in the bottom 10 bits
  int16_t const x = (int16_t) ReadADC10(0);
  int16_t const y = (int16_t) ReadADC10(1);

  int16_t const x_centered = x - JOYSTICK_RAW_MIDDLE;
  int16_t const y_centered = y - JOYSTICK_RAW_MIDDLE;

  // these scale factors convert into a uniform scale, so that
  // -JOYSTICK_OUTPUT_RANGE <= output <= JOYSTICK_OUTPUT_RANGE. The scale
  // factors have to be signed so that the multiplication produces a signed
  // value instead of converting the signed operand to an unsigned.
  static int16_t const pos_scale_factor =
    JOYSTICK_OUTPUT_RANGE / JOYSTICK_RAW_POS_RANGE;
  static int16_t const neg_scale_factor =
    JOYSTICK_OUTPUT_RANGE / JOYSTICK_RAW_NEG_RANGE;

  struct joystick_vect current;

  if (x_centered > 0) {
    current.x = x_centered * pos_scale_factor;
  } else {
    current.x = x_centered * neg_scale_factor;
  }

  if (y_centered > 0) {
    current.y = y_centered * pos_scale_factor;
  } else {
    current.y = y_centered * neg_scale_factor;
  }

  return current;
}

joystick_init()

void joystick_init

(

void

)

Initialize joystick state and peripherals.

Definition at line 53 of file joystick.c.

                         {
  PORTSetPinsDigitalIn(IOPORT_A, BIT_2);

  // ensure starts turned off
  CloseADC10();

  // Open the ADC
  uint32_t const config1 =
    // turn on
    ADC_MODULE_ON |
    // for now we don't care about this value
    ADC_IDLE_CONTINUE |
    // result in hardware buffer registers are formatted as uint16_t
    ADC_FORMAT_INTG16 |
    // internal timer for when to end sampling and begin conversion
    ADC_CLK_AUTO |
    // ADC samples continuously, as fast as it likes
    ADC_AUTO_SAMPLING_ON |
    // you can tell the ADC to hold instead of sample, but we want it to sample
    ADC_SAMP_ON;

  uint32_t const config2 =
    // use internal VREFs
    ADC_VREF_AVDD_AVSS |
    // we are not doing "offset calibration", i.e. measuring a special value to
    // compute error in normal measurements, see reference guide 17.5.4
    ADC_OFFSET_CAL_DISABLE |
    // scan through channels
    ADC_SCAN_ON |
    // interrrupt every two conversions (an interrupt per compelte joystick
    // state)
    ADC_SAMPLES_PER_INT_2 |
    // don't alternate muxA and muxB, always use muxA
    ADC_ALT_INPUT_OFF;

  uint32_t const config3 =
    // number of ADC clock cycles to sample before beginning conversion. The
    // particular number is choosen totally arbitrarily.
    ADC_SAMPLE_TIME_6 |
    // clock derived from PBCLK
    ADC_CONV_CLK_SYSTEM |
    // ADC clock prescaler: ADC clock period (TAD) is 2 * TPB
    ADC_CONV_CLK_Tcy2;

  // which ports are analog inputs
  uint32_t const configport =
    ENABLE_AN0_ANA | ENABLE_AN1_ANA;

  // which ports we _don't_ scan (scan only AN0 and AN1)
  uint32_t const configdontscan =
    SKIP_SCAN_AN2 | SKIP_SCAN_AN3 | SKIP_SCAN_AN4 | SKIP_SCAN_AN5 |
    SKIP_SCAN_AN6 | SKIP_SCAN_AN7 | SKIP_SCAN_AN8 | SKIP_SCAN_AN9 |
    SKIP_SCAN_AN10 | SKIP_SCAN_AN11 | SKIP_SCAN_AN12 | SKIP_SCAN_AN13 |
    SKIP_SCAN_AN14 | SKIP_SCAN_AN15;

  OpenADC10(config1, config2, config3, configport, configdontscan);
}

joystick_pushed()

bool joystick_pushed ( void  )

inline

Whether the joystick button is pressed.

Inteded to be polled. Any event-ish view should be provided by a state machine that consumes this.

Definition at line 148 of file joystick.c.

                                  {
  return PORTReadBits(IOPORT_A, BIT_2) != 0x0;
}