Quote:
Originally Posted by pgfpro
Nice Work!!!
How many hours so far do you have in this???

Thank you!
I think that I have put in about 6 hours, actually coding and debugging the pressure correction code. However, I spent about a week, looking at square root (and other math) algorithms, trying to get some inspiration. In the end, I figured that a simple approach was best. Coding the filtering algorithms for reading MAP voltage took about another couple of hours.
Here's the code that I am going to test later on today, on the road.
Code:
void readMAP(void) {
static unsigned long wp;
static unsigned int sample;
sampleCount = sampleTickLength  1; // reset sample timer counter
sample = sample + 3 * analogValue; // first order IIR filter  filt = filt + 3/4 * (reading  filt)
sample >>= 2;
wp = (unsigned long)(sample  analogFloor);
wp *= (unsigned long)analogSlope;
wp /= 1000ul;
pressure[MAPpressureIdx] = (unsigned int)wp;
// if vehicle is not running and is not moving, it's a fair bet that the intake manifold contains atmospheric pressure
if (!(dirty & dirtyGoodVSS) && !(dirty & dirtyGoodInj)) pressure[baroPressureIdx] = pressure[MAPpressureIdx];
// calculate differential pressure seen across the fuel injector
wp = (unsigned long)pressure[fuelPressureIdx] + (unsigned long)pressure[baroPressureIdx]  (unsigned long)pressure[MAPpressureIdx];
pressure[injPressureIdx] = (unsigned int)wp;
// to get fuel pressure ratio, multiply differential pressure by denominator factor (1 << 12), then divide by fuel system pressure
wp <<= 12;
wp /= (unsigned long)pressure[fuelPressureIdx];
// calculate square root of fuel pressure ratio
pressure[injCorrectionIdx] = iSqrt((unsigned int)wp);
}
unsigned int iSqrt(unsigned int n) {
unsigned long w = 4096; // square factor guess
unsigned int t = 4096; // proposed square root
int d; // difference between guess and proposed
int od = 0;
for (uint8_t x = 0; x < 5; x++) {
od = d;
d = n  (unsigned int)w;
d >>= 1;
t += d;
od += d;
if ((d == 0)  (od == 0)) break;
w = (unsigned long)t * (unsigned long)t;
w >>= 12;
}
return t;
}
Bemchmark testing reveals that readMap() takes about 110 us to execute, and iSqrt() takes about 33 us.