ardupilot/libraries/Desktop/support/sitl_adc.h

/*
  ADS7844 register emulation
  Code by Andrew Tridgell November 2011
 */

#ifndef _SITL_ADC_H
#define _SITL_ADC_H

#include <stdlib.h>
#include <math.h>

static float noise_scale[8] = { 240, 400, 500, 200, 400, 400, 2000, 200 };

// generate a random float between -1 and 1
static double rand_float(void)
{
	float ret = ((unsigned)random()) % 2000000;
	return (ret - 1.0e6) / 1.0e6;
}

static inline float noise_generator(uint8_t chan)
{
	extern float sitl_motor_speed[4];
	extern long unsigned int micros(void);
	uint8_t i;
	float noise = 0;
	uint8_t noise_count=0;
	double t = micros() / 1.0e6;
	for (i=0; i<4; i++) {
		if (sitl_motor_speed[i] > 0.0) {
			float n = rand_float() * noise_scale[chan];
			noise += sin(fmod(t * sitl_motor_speed[i] * 2 * 3.14 + i, 2*3.14)) * n;
			noise_count++;
		}
	}
	if (noise_count == 0) {
		return 0;
	}
	return noise/noise_count;
}

// this implements the UDR2 register
struct ADC_UDR2 {
	uint16_t value, next_value;
	uint8_t idx;
	float channels[8];

	ADC_UDR2() {
		// constructor
		for (uint8_t i=0; i<8; i++) {
			channels[i] = 0xFFFF;
		}
		value = next_value = 0;
		idx = 0;
	}

	/*
	   assignment of UDR2 selects which ADC channel
	   to output next
	*/
	ADC_UDR2& operator=(uint8_t cmd) {
		float next_analog;
		uint8_t chan;
		switch (cmd) {
		case 0x87: chan = 0; break;
		case 0xC7: chan = 1; break;
		case 0x97: chan = 2; break;
		case 0xD7: chan = 3; break;
		case 0xA7: chan = 4; break;
		case 0xE7: chan = 5; break;
		case 0xB7: chan = 6; break;
		case 0xF7: chan = 7; break;
		case 0:
		default: return *this;
		}
		next_analog = channels[chan];
		idx = 1;
		next_value = (unsigned)(next_analog + noise_generator(chan) + 0.5);
		if (next_value >= 0x1000) {
			next_value = 0xFFF;
		}
		next_value = (next_value << 3);
		return *this;
	}

	/*
	  read from UDR2 fetches a byte from the channel
	 */
	operator int() {
		uint8_t ret;
		if (idx & 1) {
			ret = (value&0xFF);
			value = next_value;
		} else {
			ret = (value>>8);
		}
		idx ^= 1;
		return ret;
	}

	/*
	  interface to set a channel value from SITL
	 */
	void set(uint8_t i, float v) {
		channels[i] = v;
	}
};

#endif // _SITL_ADC_H