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>

#define NOISE_BITS 8

static inline float noise_generator(void)
{
	extern bool sitl_motor_running;
	if (!sitl_motor_running) {
		return 0;
	}
	float noise = ((unsigned)random()) & ((1<<NOISE_BITS)-1);
	noise -= 0.5*(1<<NOISE_BITS);
	return noise;
}

// 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;
		switch (cmd) {
		case 0x87: next_analog = channels[0]; break;
		case 0xC7: next_analog = channels[1]; break;
		case 0x97: next_analog = channels[2]; break;
		case 0xD7: next_analog = channels[3]; break;
		case 0xA7: next_analog = channels[4]; break;
		case 0xE7: next_analog = channels[5]; break;
		case 0xB7: next_analog = channels[6]; break;
		case 0xF7: next_analog = channels[7]; break;
		case 0:
		default: return *this;
		}
		idx = 1;
		next_value = (unsigned)(next_analog + noise_generator() + 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