touch_xpt2046.h

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#pragma once
 
#include "roo_display/core/device.h"
#include "roo_display/driver/common/basic_touch.h"
#include "roo_display/hal/gpio.h"
#include "roo_display/hal/spi.h"
#include "roo_display/transport/spi.h"
 
namespace roo_display {
 
static const int kSpiTouchFrequency = 2500000;
 
typedef SpiSettings<kSpiTouchFrequency, kSpiMsbFirst, kSpiMode0>
    TouchXpt2046SpiSettings;
 
// If two subsequent reads are further apart than this parameter, in either
// X or Y direction, their conversion is rejected as UNSETTLED.
// This parameter helps to filter out random noise. If the value is too small,
// though, the panel may have a hard time registering touch.
static const int kMaxRawSettlingDistance = 200;
 
// How many conversions we attempt in order to get to kMinSettledConversions.
// If we reach this limit, we return the result based on however many settled
// conversions we have seen, even if it is below the minimum.
static const int kMaxConversionAttempts = 100;
 
// How many settled conversions is enough to consider the reading reliable.
static const int kMinSettledConversions = 8;
 
// How hard the press needs to be to count as touch.
static const int kInitialTouchZThreshold = 400;
 
// // How hard the press needs to be to count as continued touch (i.e., once
// // the display has been touched). See kTouchSensitivityLagMs.
// static const int kSustainedTouchZThreshold = 300;
 
// // To avoid spurious drops in drag touch, the driver is more sensitive to
// touch
// // (and thus more prone to picking up noise) for this many ms since last
// // definitive touch.
// static const int kTouchSensitivityLagMs = 250;
 
template <int pinCS, typename Spi = DefaultSpi, typename Gpio = DefaultGpio>
class TouchXpt2046 : public BasicTouchDevice<1> {
 public:
  explicit TouchXpt2046(Spi spi = Spi());
 
  virtual void initTouch() override { device_.init(); }
 
 protected:
  int readTouch(TouchPoint* points) override;
 
 private:
  typename Spi::Device<TouchXpt2046SpiSettings> device_;
 
  bool pressed_;
  unsigned long latest_confirmed_pressed_timestamp_;
};
 
// Implementation follows.
 
template <int pinCS, typename Spi, typename Gpio>
TouchXpt2046<pinCS, Spi, Gpio>::TouchXpt2046(Spi spi)
    : BasicTouchDevice(Config{.min_sampling_interval_ms = 5,
                              .touch_intertia_ms = 30,
                              .smoothing_factor = 0.8}),
      device_(spi),
      pressed_(false),
      latest_confirmed_pressed_timestamp_(0) {
  Gpio::setOutput(pinCS);
  Gpio::template setHigh<pinCS>();
}
 
template <typename Spi>
void get_raw_touch_xy(Spi& spi, uint16_t* x, uint16_t* y) {
  spi.transfer(roo::byte{0xd3});
  *x = spi.transfer16(0xd3) >> 3;
  *x = spi.transfer16(0xd3) >> 3;
  *x = spi.transfer16(0x93) >> 3;
 
  // Start bit + XP sample request for y position
  // spi.transfer(0x93);
  *y = spi.transfer16(0x93) >> 3;
  *y = spi.transfer16(0x93) >> 3;
  *y = spi.transfer16(0x00) >> 3;
}
 
template <typename Spi>
uint16_t get_raw_touch_z(Spi& spi) {
  int16_t tz = 0xFFF;
  spi.transfer(roo::byte{0xb1});
  tz += spi.transfer16(0xc1) >> 3;
  tz -= spi.transfer16(0) >> 3;
  return (uint16_t)tz;
}
 
enum ConversionResult { UNTOUCHED = 0, TOUCHED = 1, UNSETTLED = 2 };
 
template <typename Spi>
ConversionResult single_conversion(Spi& spi, uint16_t z_threshold, uint16_t* x,
                                   uint16_t* y, uint16_t* z) {
  // Wait until pressure stops increasing
  uint16_t z1 = 1;
  uint16_t z2 = 0;
  while (z1 > z2) {
    z2 = z1;
    z1 = get_raw_touch_z(spi);
  }
 
  if (z1 <= z_threshold) {
    return UNTOUCHED;
  }
 
  uint16_t x1, y1, x2, y2;
  get_raw_touch_xy(spi, &x1, &y1);
  get_raw_touch_xy(spi, &x2, &y2);
  if (abs(x1 - x2) > kMaxRawSettlingDistance) return UNSETTLED;
  if (abs(y1 - y2) > kMaxRawSettlingDistance) return UNSETTLED;
  uint16_t z3 = get_raw_touch_z(spi);
  if (z3 <= z_threshold) {
    return UNSETTLED;
  }
 
  // We have a valid touch sample pair. Return an arithmetic average as the
  // result.
  *x = (x1 + x2) / 2;
  *y = (y1 + y2) / 2;
  *z = z3;
  return TOUCHED;
}
 
template <int pinCS, typename Spi, typename Gpio>
int TouchXpt2046<pinCS, Spi, Gpio>::readTouch(TouchPoint* touch_point) {
  // long now = micros();
  int z_threshold = kInitialTouchZThreshold;
  // if (pressed_ &&
  //     (now - latest_confirmed_pressed_timestamp_ < kTouchSensitivityLagMs) &&
  //     z_threshold > kSustainedTouchZThreshold) {
  //   z_threshold = kSustainedTouchZThreshold;
  // }
 
  SpiReadWriteTransaction<pinCS, decltype(device_), Gpio> transaction(device_);
 
  int settled_conversions = 0;
  uint16_t x_tmp, y_tmp, z_tmp;
  int32_t x_sum = 0;
  int32_t y_sum = 0;
  int32_t z_max = 0;
  int count = 0;
 
  // Discard a few initial conversions so that the sensor settles.
  for (int i = 0; i < 5; ++i) {
    ConversionResult result =
        single_conversion(device_, z_threshold, &x_tmp, &y_tmp, &z_tmp);
    if (result == UNSETTLED) continue;
  }
 
  bool touched = false;
  for (int i = 0; i < kMaxConversionAttempts; ++i) {
    ConversionResult result =
        single_conversion(device_, z_threshold, &x_tmp, &y_tmp, &z_tmp);
    if (result == UNSETTLED) continue;
    settled_conversions++;
    if (result == TOUCHED) {
      touched = true;
      x_sum += x_tmp;
      y_sum += y_tmp;
      if (z_max < z_tmp) z_max = z_tmp;
      count++;
    }
    if (settled_conversions >= kMinSettledConversions) {
      // We got enough settled conversions to return a result.
      if (touched) {
        touch_point->id = 0;
        touch_point->x = 4095 - (x_sum / count);
        touch_point->y = 4095 - (y_sum / count);
        touch_point->z = z_max;
        // if (z >= kInitialTouchZThreshold) {
        //   // We got a definite press.
        //   latest_confirmed_pressed_timestamp_ = now;
        // }
      }
      pressed_ = touched;
      return pressed_ ? 1 : 0;
    }
  }
  // No reliable readout despite numerous attempts - aborting.
  pressed_ = false;
  return 0;
};
 
}  // namespace roo_display