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slavka012
Joined: 10 Feb 2012
Posts: 28
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| Problems with optimization |
 Posted: Tue Apr 09, 2013 9:25 pm |
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Running CCS compiler
CCS PCM C Compiler, Version 4.129, 59140
Executing: "C:\Program Files\PICC\Ccsc.exe" +FM "dental-main.c" +DF +LY +T +A +M -Z +Y=7 +EA #__16F1946=TRUE
----------------------------------------------------
.c:
| Code: |
M_INLINE void Encrypt(unsigned char source[], unsigned char number) {
// this is supposed to be a const, but error in CCS compiler
// does not allow it hence we get a warning
unsigned char *pass_ptr = Passphrase + PassphraseIndex;
unsigned int8 TmpIndex = PassphraseIndex;
int i = 0;
for (i = 0; i < number; i++ ) {
source[i] = source[i] ^ (Passphrase[TmpIndex]);
pass_ptr++;
TmpIndex++;
if (TmpIndex >= sizeof(Passphrase)) {
TmpIndex = 0;
pass_ptr = Passphrase;
};
};
}
M_SEPARATE void AdvancePassphrase() {
PassphraseIndex = (PassphraseIndex + PassphraseInc);
PassphraseIndex = PassphraseIndex % sizeof(Passphrase);
}
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.lst file:
024 PassphraseIndex
.asm:
| Code: | 34: M_SEPARATE void AdvancePassphrase() {
35: PassphraseIndex = (PassphraseIndex + PassphraseInc);
0707 300D MOVLW 0xd
0708 07A4 ADDWF 0x24, F
36: PassphraseIndex = PassphraseIndex % sizeof(Passphrase);
0709 13A4 BCF 0x24, 0x7
37: }
070A 0008 RETURN
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The problem here is that compiler does not set the BSR inside the AdvancePassphrase function.
It is sort of set before the call to AdvancePassphrase:
| Code: | 1135 0020 MOVLB 0
140: AdvancePassphrase();
1189 3180 MOVLP 0
118A 2707 CALL AdvancePassphrase
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However the "movlb 0" is never executed. I set the PC to the preceding function:
| Code: |
Encrypt(SerialBuff+1, REQ_ADC_RESPONSE_SIZE);
AdvancePassphrase();
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And execution never goes to movlb. The function is executed with BSR=0x5, and does not really update PassphraseIndex.
That's pretty horrible. I spend whole day figuring this one out - the code was working before. Today I set optimization to a higher level because the code did not fit into the memory anymore.
Last edited by slavka012 on Tue Apr 09, 2013 9:55 pm; edited 1 time in total |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Apr 09, 2013 9:40 pm |
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This means you are running #opt 7. The default opt level is 9.
I never change the #opt level. To do so, means you're running an
untested version of the compiler. 99.9% of the people on this forum
are using the default level, I would bet. So any bugs we find are
for the #opt 9 default level. No one really knows what the compiler
is doing for other #opt levels. I don't think they are tested by anyone.
Don't use them. And don't ask why #opt is included, lol. |
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slavka012
Joined: 10 Feb 2012
Posts: 28
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| Posted: Tue Apr 09, 2013 10:00 pm |
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Hm... You might be right. I checked at #opt level 9, it works correctly. It works at level 6 and below as well.
I can't recall why I lowered it in the first place. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19540
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| Posted: Wed Apr 10, 2013 12:48 am |
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I think 'black art' at opt=7. 
I think PCM programmer is 'spot on'. 99.9% of code will be at default, with the occasional 'test' at opt=0, if you think you have an optimisation problem.
Some years ago, there were some memory management problems which were fixed by dropping a couple of levels.
Best Wishes |
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