speeduino/utils.h

/*
These are some utility functions and variables used through the main code
*/ 
#include <Arduino.h>
#define MS_IN_MINUTE 60000
#define US_IN_MINUTE 60000000


/* The following functions help determine the required fuel constant. For more information about these calculations, please refer to http://www.megamanual.com/v22manual/mfuel.htm
  Calc below are for metric inputs of temp (degrees C) and MAP (kPa) to produce kg/m3.
*/
int AIRDEN(int MAP, int temp)
  {
	return (1.2929 * 273.13/(temp+273.13) * MAP/101.325);
  }

/*
This function retuns a pulsewidth time (in us) using a hybrid Alpha-N algorithm, given the following:
REQ_FUEL
VE: Lookup from the main MAP vs RPM fuel table
MAP: In KPa, read from the sensor
GammaE: Sum of Enrichment factors (Cold start, acceleration). This is a multiplication factor (Eg to add 10%, this should be 110)
injDT: Injector dead time. The time the injector take to open minus the time it takes to close (Both in uS)
TPS: Throttle position (0% to 100%)

This function is called by PW_SD and PW_AN for speed0density and pure Alpha-N calculations respectively. 
*/
int PW(int REQ_FUEL, byte VE, byte MAP, int GammaE, int injOpen, byte TPS)
  {
    //Standard float version of the calculation
    return (REQ_FUEL * (float)(VE/100.0) * (float)(MAP/100.0) * (float)(GammaE/100.0) + injOpen);
    
    //100% float free version, does sacrifice a little bit of accuracy. Accuracy loss is in the order of 0.1ms (100uS)
    
    int iVE = ((int)VE << 7) / 100;
    int iMAP = ((int)MAP << 7) / 100;
    int iGammaE = (GammaE << 7) / 100;
    int iTPS = ((int)TPS << 7) / 100;

    unsigned long intermediate = ((long)REQ_FUEL * (long)iVE) >>7; //Need to use an intermediate value to avoid overflowing the long
    intermediate = (intermediate * iMAP) >> 7;
    intermediate = (intermediate * iGammaE) >> 7;
    intermediate = (intermediate * iTPS) >> 7;
    return (int)intermediate + injOpen;

  }
 
//Convenience function for Speed Density 
int PW_SD(int REQ_FUEL, byte VE, byte MAP, int GammaE, int injOpen)
{
  return PW(REQ_FUEL, VE, MAP, GammaE, injOpen, 100); //Just use 1 in place of the TPS
}

int PW_AN(int REQ_FUEL, byte VE, byte TPS, int GammaE, int injOpen)
{
  return PW(REQ_FUEL, VE, 100, GammaE, injOpen, TPS); //Just use 1 in place of the MAP
}

/* Determine the Gamma Enrichment number. Forumla borrowed from MS2 manual... may be skipped/simplified for arduino!
WARMUP: Warmup Correction 
O2_CLOSED: Feedback from Closed Loop Operation
AIRTEMP: Air Temp correction <-- Skip?
BARO: Barometric Correction <-- Skip?
*/

int GammaE( int WARMUP, int O2_CLOSED, int AIRTEMP, int BARO)
  {
    return (WARMUP/100) * (O2_CLOSED/100) * (AIRTEMP/100) * (BARO/100);
  }