touch.c

/* Teensyduino Core Library
 * http://www.pjrc.com/teensy/
 * Copyright (c) 2013 PJRC.COM, LLC.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * 1. The above copyright notice and this permission notice shall be 
 * included in all copies or substantial portions of the Software.
 *
 * 2. If the Software is incorporated into a build system that allows 
 * selection among a list of target devices, then similar target
 * devices manufactured by PJRC.COM must be included in the list of
 * target devices and selectable in the same manner.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "core_pins.h"
//#include "HardwareSerial.h"

static const uint8_t pin2tsi[] = {
//0    1    2    3    4    5    6    7    8    9
  9,  10, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255,  13,   0,   6,   8,   7,
255, 255,  14,  15, 255,  12, 255, 255, 255, 255,
255, 255,  11,   5
};

// These settings give approx 0.02 pF sensitivity and 1200 pF range
// Lower current, higher number of scans, and higher prescaler
// increase sensitivity, but the trade-off is longer measurement
// time and decreased range.
#define CURRENT   2 // 0 to 15 - current to use, value is 2*(current+1)
#define NSCAN     9 // number of times to scan, 0 to 31, value is nscan+1
#define PRESCALE  2 // prescaler, 0 to 7 - value is 2^(prescaler+1)


// output is approx pF * 50
// time to measure 33 pF is approx 0.25 ms
// time to measure 1000 pF is approx 4.5 ms

int touchRead(uint8_t pin)
{
	uint32_t ch;

	if (pin >= NUM_DIGITAL_PINS) return 0;
	ch = pin2tsi[pin];
	if (ch == 255) return 0;

	*portConfigRegister(pin) = PORT_PCR_MUX(0);
	SIM_SCGC5 |= SIM_SCGC5_TSI;
	TSI0_GENCS = 0;
	TSI0_PEN = (1 << ch);
	TSI0_SCANC = TSI_SCANC_REFCHRG(3) | TSI_SCANC_EXTCHRG(CURRENT);
	TSI0_GENCS = TSI_GENCS_NSCN(NSCAN) | TSI_GENCS_PS(PRESCALE) | TSI_GENCS_TSIEN | TSI_GENCS_SWTS;
	delayMicroseconds(10);
	while (TSI0_GENCS & TSI_GENCS_SCNIP) ; // wait
	delayMicroseconds(1);
	return *((volatile uint16_t *)(&TSI0_CNTR1) + ch);
}