Strange Error again

Thomas · August 27, 2006, 12:53pm

Hallo!

I wrote something like:

----------------------- VERSION that works ---------------------

void switchLEDs(unsigned char pattern, unsigned char and){

unsigned char i;

unsigned char pos;

for (i = 0; i < 8; i++){

MIOS_DOUT_PinSet1(32);

MIOS_DOUT_PinSet1(33);

MIOS_DOUT_PinSet1(34);

MIOS_DOUT_PinSet1(35);

MIOS_DOUT_PinSet1(36);

MIOS_DOUT_PinSet1(37);

}

This works.

BUT: all trials to make the pin setting dynamically depending on i failed!

----------------------- VERSION 1 that does not work ---------------------

void switchLEDs(unsigned char pattern, unsigned char and){

unsigned char i;

unsigned char pos;

for (i = 0; i < 8; i++){

MIOS_DOUT_PinSet1(32 + i);

}

This do not work, even if I use the temporär variable pos to store the result

of 32 + i. I thougth: ok, if it is a compiler bug and MIOS_DOUT_PinSet1 needs a contant parameter I reprogrammed it:

----------------------- VERSION 2 that does not work ---------------------

void switchLEDs(unsigned char pattern, unsigned char and){

unsigned char i;

unsigned char pos;

MIOS_DOUT_PinSet1(37); //see below!

for (i = 0; i < 8; i++){

switch(i){

case 0: MIOS_DOUT_PinSet1(32); break;

case 1: MIOS_DOUT_PinSet1(33); break;

case 2: MIOS_DOUT_PinSet1(34); break;

case 3: MIOS_DOUT_PinSet1(35); break;

case 4: MIOS_DOUT_PinSet1(36); break;

case 5: MIOS_DOUT_PinSet1(37); break;

}

This didn’t work, too. No pin is set, except pin 37. This was to indicate the function itselfs is called. I tried another version, with ifs:

----------------------- VERSION that works ---------------------

void switchLEDs(unsigned char pattern, unsigned char and){

unsigned char i;

unsigned char pos;

MIOS_DOUT_PinSet1(37);

for (i = 0; i < 8; i++){

if (i == 0) MIOS_DOUT_PinSet1(32);

else if (i == 1) MIOS_DOUT_PinSet1(33);

else if (i == 2) MIOS_DOUT_PinSet1(34);

else if (i == 3) MIOS_DOUT_PinSet1(35);

else if (i == 4) MIOS_DOUT_PinSet1(36);

else if (i == 5) MIOS_DOUT_PinSet1(37);

}

Even this did not work! Only LED 37 ligths.

If I look at the *.asm the call of MIOS_DOUT_PinSet1(constant) is always the same. Independently if there are switches or ifs around it. But only the “pure” constant method above works.

I have no ideas. The *.asm seem to be ok.

As you can guess, the parameter “pattern” is the bit-pattern which of the LEDs 32-37 shall lit. But this is future…even the primitive varants do not work.

I have no idea.

T.K · August 27, 2006, 1:43pm

Hi Thomas,

which SDCC version are you using? 2.6.0 sometimes behaves strange, 2.5.0 works ok - undefined snapshot versions (with immediate bugs) shouldn’t be used.

What happens when you are adding following code to the switchLEDs function:

void switchLEDs(unsigned char pattern, unsigned char and){
  unsigned char i;
  unsigned char pos;

  MIOS_MIDI_BeginStream(); // for debugging
  MIOS_MIDI_TxBufferPut(0xf0);

  for (i = 0; i < 8; i++){
      MIOS_MIDI_TxBufferPut(32 + i); // for debugging
      MIOS_DOUT_PinSet1(32 + i);
      MIOS_MIDI_TxBufferPut(MIOS_DOUT_PinGet(32 + i)); // for debugging
  }

  MIOS_MIDI_TxBufferPut(0xf7); // for debugging
  MIOS_MIDI_EndStream();
}
[/code]









Best Regards, Thorsten.

Thomas · August 27, 2006, 3:13pm

Hi Thorsten!

I’m using 2.5.0 #1020 (8.Mai 2005).

But I could solve the problem.

The main problem was that in reality the 8 in the for-statement was no a 8, but a defined constant.

for (i = 0; i < (NO_OF_BUTTONS - POS_OF_SPECIAL_LEDS); i++) …

where

#define NO_OF_BUTTONS 40

#define POS_OF_SPECIAL_LEDS NO_OF_BUTTONS - 8

I forgot the brackets - changing it to:

#define POS_OF_SPECIAL_LEDS (NO_OF_BUTTONS - 8)

seems to work.

That my mistake.

BUT:

during debugging I changed it to “8” sometimes - no result.
The resulting *asm depend if there are only constants or a variable parameter in the for-block.

Assuming that in th upper case POS_OF_SPECIAL_LEDS is defined as NO_OF_BUTTONS so (NO_OF_BUTTONS - POS_OF_SPECIAL_LEDS) == 0.

I would assume the for-statement is executed never. As it is.

But it is executed 8 times if ther are only constants in the body. Seems that the preprocessor calculates the values differently, depending on the body.

I changed your examble so that every time a complete MIDI-controller valus was sent.

Summary:

VERSION 1:

------------- in Header file -------------

#define NO_OF_BUTTONS 40

#define POSOFSPECIALLEDS NO_OF_BUTTONS - 8

------------- in function file -------------

void switchLEDs(unsigned char pattern, unsigned char and){

unsigned char i;

unsigned char pos;

MIOS_MIDI_BeginStream();

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(0x00);

MIOS_MIDI_TxBufferPut(0x11);

for (i = 0; i < (NO_OF_BUTTONS - POS_OF_SPECIAL_LEDS); i++){

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(32); //constant!

MIOS_MIDI_TxBufferPut(0x22);

MIOS_DOUT_PinSet1(32); //constant!

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(MIOS_DOUT_PinGet(32)); //constant!

MIOS_MIDI_TxBufferPut(0x33);

}

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(0x00);

MIOS_MIDI_TxBufferPut(0x44);

MIOS_MIDI_EndStream();

}

I got:

BB 00 11

BB 20 22… 90 times in sum!*

BB 01 33… 102 times in sum!*

BB 00 44

* the order is mismatched:

BB 20 22

BB 01 33

BB 20 22

BB 01 33

BB 20 22

…

VERSION 2:

------------- in Header file -------------

#define NO_OF_BUTTONS 40

#define POSOFSPECIALLEDS NO_OF_BUTTONS - 8

------------- in function file -------------

void switchLEDs(unsigned char pattern, unsigned char and){

unsigned char i;

unsigned char pos;

MIOS_MIDI_BeginStream();

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(0x00);

MIOS_MIDI_TxBufferPut(0x11);

for (i = 0; i < (NO_OF_BUTTONS - POS_OF_SPECIAL_LEDS); i++){

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(32+i);

MIOS_MIDI_TxBufferPut(0x22);

MIOS_DOUT_PinSet1(32+i);

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(MIOS_DOUT_PinGet(32+i));

MIOS_MIDI_TxBufferPut(0x33);

}

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(0x00);

MIOS_MIDI_TxBufferPut(0x44);

MIOS_MIDI_EndStream();

}

I only got: (as you would expect)

BB 00 11

BB 00 44

VERSION 3: (The right one)

------------- in Header file -------------

#define NO_OF_BUTTONS 40

#define POSOFSPECIALLEDS (NO_OF_BUTTONS - 8)

------------- in function file -------------

void switchLEDs(unsigned char pattern, unsigned char and){

unsigned char i;

unsigned char pos;

MIOS_MIDI_BeginStream();

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(0x00);

MIOS_MIDI_TxBufferPut(0x11);

for (i = 0; i < (NO_OF_BUTTONS - POS_OF_SPECIAL_LEDS); i++){

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(32+i);

MIOS_MIDI_TxBufferPut(0x22);

MIOS_DOUT_PinSet1(32+i);

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(MIOS_DOUT_PinGet(32+i));

MIOS_MIDI_TxBufferPut(0x33);

}

MIOS_MIDI_TxBufferPut(0xbb);

MIOS_MIDI_TxBufferPut(0x00);

MIOS_MIDI_TxBufferPut(0x44);

MIOS_MIDI_EndStream();

}

I got what I want…

BB 00 11

BB 20 22

BB 01 33

BB 21 22

BB 01 33

BB 22 22

BB 01 33

BB 23 22

BB 01 33

BB 24 22

BB 01 33

BB 25 22

BB 01 33

BB 26 22

BB 01 33

BB 27 22

BB 01 33

BB 00 44

Strange, isn’t it?

T.K · August 27, 2006, 7:38pm

I don’t find this so strange - i is an unsigned variable, it can never be < 0

Therefore the behaviour of:

for(i=0; i<0; ++i)

is undefined and heavily depends on the C compiler implementation (a good C compiler prints a warning in this case)

Best Regards, Thorsten.

P.S.: yes, those missing brackets are not uncommon, all of my students @work are making this error once during their practical year

Thomas · August 27, 2006, 11:03pm

Hi Thorsten!

I find it strange. :-\

is undefined and heavily depends on the C compiler implementation (a good C compiler prints a warning in this case)

Your right. But the warning always says something like this:

"test.cpp:8: warning: comparison is always false due to limited range of data typ

e" (gcc, g++)

I will check this with Visual C++ later.

I always thought this statement was clear (always false) and is not undefined.

P.S.: yes, those missing brackets are not uncommon, all of my students @work are making this error once during their practical year

Maybe. But I knew that there must be brackets. I simply forgot them because I normally program JAVA (at work) and C++ and Python (at Home). So I never use preprocessor-directives for constants anymore (I read my Scott Meyers well… ;)) .

And all other variants don’t need brackets…

Thomas · August 28, 2006, 6:22pm

Hi!

FYI: Weil mich das jetzt sehr interessiert hat und ich (auf die Schnelle) darüber nichts finden konnte, habe ich die Frage in den einschlägigen Newsgroups gestellt.

Einhellige Meinung: die Bedingung müsste immer falsch sein, die Schleife nie durchlaufen werden. SDCC macht also hier sein eigenes Ding. (was aber nicht so schlimm ist, da es eh kein ANSI-C ist. Nur man muss es halt wissen.)