Q about $8D bpw calculation
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From: Greenwich, CT
Q about $8D bpw calculation
RBob, may I ask a Q about the $8D mask? I haven't seen this in the archives anywhere.
Somebody on another board was wondering how the bpw calc is done in 8D,
and once I started looking at it, I realized I can't folllow the code with any degree of certainty.
Could you please help interpret how the ECM is calculating engine air/fuel flow?
The code below is from the ANHT hack on the ECMGuy site, about 55% of the way
down through the text. If my formatting works, the code is on the left & my confusion
notes on the right. Looking at the code:
It looks like it takes the ideal gas law for the grams of air in 1 cyl, and then
corrects it for VE (=L006F?); then calc's an air RATE for that RPM;
then corrects it to a flow for 4 cyl/crank rev ( 4 DRP = 1 crank rev?).
Then a term 'EGR0' appears that I don't understand - is that part of the
assembly code? I didn't see it anywhere else.
Then it seems to multiply X 2, to give an air rate for 8 cyl???? This number
then seems to be forgotten(=L006B?).
After that it seems to take the calc'd air per cyl (L006F?) and multiply it by
the 'commanded AFR' (I imagine that should be 1/AFR) to get a fuel weight.
Somehow it converts the fuel weight into a PW from the sec/gram rating of
ONE inj, but how that math is done is confounding me - since again they
are using 1 DRP. One DRP is one quarter of a crank rev, is it not?
Seems like that bpw would result in 2X as much fuel as you need, if you
are firing the inj's once per crank rev.
Anyway, thanks in advance for any light you can shed on the code.
This is done for my own curiosity - I am not in the chip business,
this is just a hobby
.
DrJ
Somebody on another board was wondering how the bpw calc is done in 8D,
and once I started looking at it, I realized I can't folllow the code with any degree of certainty.
Could you please help interpret how the ECM is calculating engine air/fuel flow?
The code below is from the ANHT hack on the ECMGuy site, about 55% of the way
down through the text. If my formatting works, the code is on the left & my confusion
notes on the right. Looking at the code:
It looks like it takes the ideal gas law for the grams of air in 1 cyl, and then
corrects it for VE (=L006F?); then calc's an air RATE for that RPM;
then corrects it to a flow for 4 cyl/crank rev ( 4 DRP = 1 crank rev?).
Then a term 'EGR0' appears that I don't understand - is that part of the
assembly code? I didn't see it anywhere else.
Then it seems to multiply X 2, to give an air rate for 8 cyl???? This number
then seems to be forgotten(=L006B?).
After that it seems to take the calc'd air per cyl (L006F?) and multiply it by
the 'commanded AFR' (I imagine that should be 1/AFR) to get a fuel weight.
Somehow it converts the fuel weight into a PW from the sec/gram rating of
ONE inj, but how that math is done is confounding me - since again they
are using 1 DRP. One DRP is one quarter of a crank rev, is it not?
Seems like that bpw would result in 2X as much fuel as you need, if you
are firing the inj's once per crank rev.
Anyway, thanks in advance for any light you can shed on the code.
This is done for my own curiosity - I am not in the chip business,
this is just a hobby
.DrJ
Code:
*************************************************** * CALCULATE SPEED DENSITY * * ANHT, TYPE $8D ECM *************************************************** ;----------------------------- ; GMS of AIR per CYLINDER ; (CALC VE) ;----------------------------- LDX L006D ; GET INV MAT OK, I know what Inv MAT is LDD L0079 ; MAP FOR SP/DENS CALC OK, I know what MAP is SUBD L0069 ; PARTIAL PRESS DUE TO EGR Let's ignore EGR for now ; SUB OFF EGR PART PRESSURE BCC LCC40 ; IF NO UNDERFLOW ; ... else CLRA ; LIMIT, (MAP-EGR) = 0 CLRB ; ; VE CALC = ((MAP - EGR part press) * CYL VOL)/((MAT + 233) * 128)) This looks like ideal gas law=1 cyl ; LCC40: JSR LE424 ; 16 * 16 )RET W MIDDLE 2 BYTES IN D) 16X16 = multiply 2 16 bit terms? PSHB PSHA TSX ; Point to VE CAL ON STACK LDAA L0067 ; FILTERED V.E, (TRACKING) =get current VE from memory JSR LE33F ; 8 x 16 MULT, 8X16 bit multiplication? STD L006F ; GRAMS AIR/CYL =grams or air in 1 cyl X VE PULX ; CLR STX ;---------------------- ; CALC AIR FLOW USING OK, above we calc'd corrected grams ; IDEAL GAS LAW air in 1 cyl; so now what's EGR0? ;--------------------- LDX L00B3 ; CURRENT MNR LOOP DRP PERIOD =get DRP time from memory IDIV ; X = (((EGR0 * INV MAT) * VE * 1/DRP PER =grams air/time for 1/4 crank rev? ; does that give air RATE for 4 cyl?? ; REMAINDER TO STX ; PSHB PSHA PSHX ; ; GET INTEGER PORTION ; PULA PULB ASLD ; Mult * 2, FOR SCALE =X2 gives a rate for 8 cyl??? STD L0064 ; SAVE INTG PART OF AIR FLOW ; ; REMAINDER FROM STX ; PULA ; PULB ; LDX L00B3 ; CURRENT MNR LOOP DRP PERIOD FDIV ; FRACT = REMAINDER PSHX ; 16 bit FRACT TO STX PULA PULB ASLD ; SCALE & ROUND FRACT STAA L0066 ; SAVE FRACT PART OF AIR FLOW BCC LCC6B ; BR IF NO FRACT OVERFLOW ; ... else LDX L0064 ; GET INTEG AIR FLOW INX ; INCR FRO FRACT STX L0064 ; AIR FLOW LCC6B: TAB ; FRACT TO B Reg LDAA L0065 ; GET LO BYTE ON INTEG BRCLR L0064,#$FF,LCC75 ; BR TO SPD DENS CALC IF ; AIR FLOW LT 256 G/SEC ; ... else LDD #$FFFF ; LIMIT TO 255.996 Gms\ =max flow for 8 cyl = 256 g/sec? LCC75: STD L006B ; SAVE LIMITED AIR FLOW FM IDEAL GAS LAW where does L006B get used? ;---------------------------- ; SPEED DENS BPW CALCULATION ;---------------------------- LDD L006F ; GRAMS AIR/CYL =grams/ 1 cyl corrected for VE LDX L00F1 ; FINAL TOTAL AF VAL =commanded AFR JSR LE424 ; 16 * 16 )RET W MIDDLE 2 BYTES IN D) ???? LDX $841C ; SEC/GRAM PROD OF INJ FLOW Rate, =inj PW in sec/gram???? ; (0.359 SEC/GRAM, 2.86 g/Sec) JSR LE3EE ; 16 x 16 (RET W/UPPER 2 BYTES IN D) ROLB ; MULT X 2 why X2 ?? Inj's fire 1 time in 4 DRP? ROLA seems like it should be /2 ??? STD L00E2 ; Base Pulse width ;-------------------------------------------------- ;-------------------------------------------------- ; DO BLM CORRECTION Worry about the BLMs later.. ;
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From: Chasing Electrons
Car: check
Engine: check
Transmission: check
I've found that when it comes to GM code some things are almost impossible (or at least tedious) to follow to the exact value. A simulator would be helpful, or a calulator and lots of paper 
Math scaling is the foremost in this area. There is all kinds of scaling going on. The AFR is an inverse term: ARG = 6553.6/AFR_RATIO.
Then the injector flow is scaled: ARG = ((SEC/GRAM * 256) * 5). It isn't even in gms/sec or #'s/hr, it is in seconds to flow 1 gram of fuel times 256 times 5.
The cylinder volume is used to scale the MAT term before it is used in this routine.
L86DD: FDB 159 ; CYL VOL & UNIT CONV, (0.7125 LITRE/CYL)
; (CAL = L/CYL * 223.157)
The three multiply routines are scaling the result before it is returned.
The 8 x 16 routine (an 8 bit value times a 16 bit value) returns a value that is the result divided by 256:
JSR LE33F ; 8 x 16 MULT, AB = (A * *X) / 256
One of the 16 x 16 routine returns a value that is the result multiplied by 256:
JSR LE424 ; 16 x 16 MULT, AB = (AB * X) * 256 (RET W MIDDLE 2 BYTES IN D)
Another 16 x 16 routine returns a value that is the result multiplied by 65536:
JSR LE3EE ; 16 x 16 MULT, AB = (AB * X) * 65536 (RET W/UPPER 2 BYTES IN D)
An example of how this multiply/scaling is used is where the airflow is multiplied by the VE:
The VE is a percentage of what amount out of 100% will actually flow into the cylinder. The math routine will do exactly that. It will multiply the airflow by the VE value and then divide by 256. This will reduce the airflow by the VE%.
The 'EGR0' looks to be used just to show that the EGR flow has been subtracted out of the air flow. It's inert so it doesn't count. The way the comment is written may also be a mistake.
The L00B6 airflow term is used in the closed loop fueling for integral & proportional gains/delays.
Yes, one DRP is the time it takes to move 90 degrees of crank rotation. It is the number of clock ticks between each DRP. The ticks run at 65,536 a second, or 15.26 usec/tick.
There is a comment in the hac about the injector flow rate that is interesting:
Single Fire #/h = 20317.6/cal val
Using this the 22#/hr injectors are seen as 44#/hr injectors. That may be the scaling factor you are looking for.
RBob.
Math scaling is the foremost in this area. There is all kinds of scaling going on. The AFR is an inverse term: ARG = 6553.6/AFR_RATIO.
Then the injector flow is scaled: ARG = ((SEC/GRAM * 256) * 5). It isn't even in gms/sec or #'s/hr, it is in seconds to flow 1 gram of fuel times 256 times 5.
The cylinder volume is used to scale the MAT term before it is used in this routine.
L86DD: FDB 159 ; CYL VOL & UNIT CONV, (0.7125 LITRE/CYL)
; (CAL = L/CYL * 223.157)
The three multiply routines are scaling the result before it is returned.
The 8 x 16 routine (an 8 bit value times a 16 bit value) returns a value that is the result divided by 256:
JSR LE33F ; 8 x 16 MULT, AB = (A * *X) / 256
One of the 16 x 16 routine returns a value that is the result multiplied by 256:
JSR LE424 ; 16 x 16 MULT, AB = (AB * X) * 256 (RET W MIDDLE 2 BYTES IN D)
Another 16 x 16 routine returns a value that is the result multiplied by 65536:
JSR LE3EE ; 16 x 16 MULT, AB = (AB * X) * 65536 (RET W/UPPER 2 BYTES IN D)
An example of how this multiply/scaling is used is where the airflow is multiplied by the VE:
Code:
TSX ; Point to VE CAL ON STACK (really the airflow here!)
LDAA L0067 ; FILTERED V.E, (TRACKING) =get current VE from memory
JSR LE33F ; 8 x 16 MULT, AB = (A * *X) / 256
STD L006F ; GRAMS AIR/CYL =grams or air in 1 cyl X VE The 'EGR0' looks to be used just to show that the EGR flow has been subtracted out of the air flow. It's inert so it doesn't count. The way the comment is written may also be a mistake.
The L00B6 airflow term is used in the closed loop fueling for integral & proportional gains/delays.
Yes, one DRP is the time it takes to move 90 degrees of crank rotation. It is the number of clock ticks between each DRP. The ticks run at 65,536 a second, or 15.26 usec/tick.
There is a comment in the hac about the injector flow rate that is interesting:
Single Fire #/h = 20317.6/cal val
Using this the 22#/hr injectors are seen as 44#/hr injectors. That may be the scaling factor you are looking for.
RBob.
Thread Starter
Member
Joined: Jun 2001
Posts: 146
Likes: 0
From: Greenwich, CT
RBob,
Many thanks for your time.
I hadn't figured out what the 'JSR' was for - apparently it
calls a 'xxx.SRC' routine?
That helps a lot. I'll go back to picking at it.
BTW, I noticed that 'single fire' comment too - somewhere
early in the text was a line to the effect 'single fire'
was invoked when the bpw got below ~1 ms.
Thanks again.
DrJ
Many thanks for your time.
I hadn't figured out what the 'JSR' was for - apparently it
calls a 'xxx.SRC' routine?
That helps a lot. I'll go back to picking at it.
BTW, I noticed that 'single fire' comment too - somewhere
early in the text was a line to the effect 'single fire'
was invoked when the bpw got below ~1 ms.
Thanks again.
DrJ
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