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nyet
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« Reply #15 on: February 12, 2021, 01:18:21 PM »
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0054, 00, ps_w , 0, {mbar }, 0, 0, 0.0390625, 0, {Saugrohr-Absolutdruck (Word)}
From s4wiki page Absolute maximum measured boost is 0xffff/25.6 = 2559.96 mBar (DSLOFS = 0), and 2543.55 mBar (DSLOFS=-16.40646)
1*10/256 = ? |
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« Last Edit: February 12, 2021, 01:21:47 PM by nyet »
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IWay
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« Reply #16 on: February 15, 2021, 05:20:13 AM »
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Thanks for your patience on this, but you might have to spell it out.
I can see the relationship between the numbers, but I'm failing to see where the limit is encountered other than in the code.
If the limit is in the code can't we just change the code to;
0054, 00, ps_w , 0, {mbar }, 0, 0, 0.078125, 0, {Saugrohr-Absolutdruck (Word)}
IE
0xffff/12.8 = 5119.92 mBar
Or Am I completely missing something?
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nyet
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« Reply #17 on: February 15, 2021, 03:00:13 PM »
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Thanks for your patience on this, but you might have to spell it out.
I can see the relationship between the numbers, but I'm failing to see where the limit is encountered other than in the code.
If the limit is in the code can't we just change the code to;
0054, 00, ps_w , 0, {mbar }, 0, 0, 0.078125, 0, {Saugrohr-Absolutdruck (Word)}
IE
0xffff/12.8 = 5119.92 mBar
Or Am I completely missing something?
That's not the code. That is just the logger translating what it is logging into a human readable format. |
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IWay
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« Reply #18 on: February 16, 2021, 02:58:37 AM »
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Sorry,
Just not getting it,
16 Bit = unsigned 65K numbers, signed 32k positive & 32K negative.
Did notice that 2559.96 x 0.039063 = 99.999, so the presure range is represented by 0 to 100 decimal?updated post, This is wrong, pressure range not represented by 0 to 100 decimal
Sure once it's spelt out I'll go AHH, that's obvious or that's strange who thought of doing it that way!
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« Last Edit: February 18, 2021, 02:04:02 AM by IWay »
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nyet
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« Reply #19 on: February 16, 2021, 06:17:15 PM »
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If the limit is in the code can't we just change the code to;
0054, 00, ps_w , 0, {mbar }, 0, 0, 0.078125, 0, {Saugrohr-Absolutdruck (Word)}
This is literally what the 5120 hack does. It modifies the ECU so that is true. Unless you follow exactly every bit of ASM change recommended, you are not doing what you just asked. |
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IWay
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« Reply #20 on: February 17, 2021, 02:30:19 AM »
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Think I'm getting it now;
65535 x 0.039063 = 25.6
So 1mBar = 25.6 units in the code.
So the developers decided that they would use 25.6, not 12.8, 51.2 or some other number to factor the mBar value?
Strange why not just use 1 to 1??
IE, it’s a code limit not a hardware limit.
The term “hard limit”, is what has been throwing me, was beginning to think that there was some smoke & mirrors going on.
So we are changing the code to scale, 1mBar = 12.8 units in the code.
Then we are doubling or halving the maps as required to accommodate the higher possible mBar value.
So it could be called the 12.8 hack!
Please tell me the above is correct or it will be time to sit in the corner & start rocking back and forth.
Thanks
PS
I’ve got it working a treat.
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nyet
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« Reply #21 on: February 17, 2021, 03:21:10 AM »
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Nope now you've got it.
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IWay
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« Reply #22 on: February 17, 2021, 04:10:26 AM »
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Cool,
Stlll strange they didn't use 1 to 1?
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nyet
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« Reply #23 on: February 17, 2021, 01:22:21 PM »
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Cool,
Stlll strange they didn't use 1 to 1?
That would be pretty terrible resolution and would completely confuse the PID due to quantization error |
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prj
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« Reply #24 on: February 17, 2021, 01:56:42 PM »
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Diesel uses 1:1 in mbar and has no issue. 1:1 is just fine.
These sensors are not even specified to that precision.
It's done like this for no particular reason whatsoever.
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IWay
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« Reply #25 on: February 18, 2021, 02:00:42 AM »
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It's probably a hangover from something previous, I've seen it before from developers. The developer thought process goes, "if it works why change it and it's quicker to use something that's already there and working than start again" Probably got it from some industrial or scientific process that needs the extra accuracy, Bosch do all sorts of things. Or they just did it to be awkward  |
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nyet
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« Reply #26 on: February 18, 2021, 02:11:27 AM »
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yah it is sort of arbitrary, but there are only a few commonly used 16 bit scales in ME7, i guess they picked the one that was easiest to use.
Very few 16 bit values are 1:1 (are there any actually? I should go look) , since presumably engineers all think they need float ability, though ya, if it was Bar it would make sense, but mBar?
interesting discussion.
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d3irb
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« Reply #27 on: February 18, 2021, 07:56:33 AM »
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Remember as we start trying to infer "what were the developers thinking" (which is half the fun of RE!) that a lot of model code is codegen, not hand-written (more and more so as we reach newer ECUs).
So the decision to use this arbitrary-seeming precision, even back in the ME7 days, just as well may have been driven by which value types easily or natively plugged into some block or another in whatever modelgen software was in use - I think for ME7 this was probably ASCET, more modern stuff is moving more and more to Simulink.
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prj
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« Reply #28 on: February 18, 2021, 10:55:18 AM »
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Up until MED17 the C code was written mostly by hand.
At end of MED17 and with MG1, everything is autogen.
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IWay
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« Reply #29 on: February 19, 2021, 02:26:05 AM »
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Autogen! I know how this ends, I've seen Terminator and Dark Star  |
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