Initialising a Variable

[robinfawell]

I have a problem where I have variable "record_button_state" that is not behaving as I want.

I would like it to have an initial value of 17(dec).

I have tried to initialise it by the global declaration :-

unsigned char record_button_state = 17;

However in testing the result, using Midi-ox I find that the inital value is 0 not 17.

The variable picks up another value in operation.  It should have  values of 16 and 17 during the operation of the system but not 0.

Please help.

Robin

[jackchaos]

declare the variable 1st, then assign a value like so:

unsigned char button_state;

button_state = 17;

[robinfawell]

Thanks jackchaos,

I've already tried that.  In my program the value 17 is picked and the value stays at 17.  I need to initialise the value outside the function somehow then allow the function to change the value from (say) 17 to 16 during the operation.

Robin

[audiocommander]

Hi Robin,

I'm using variables this way:

variable declaration (or) declaration and initialisation

This is done in the .c-file at the top, outside any function:

[tt]unsigned char record_button_state;[/tt] (or)

[tt]unsigned char record_button_state = 17;[/tt]

The additional keyword "volatile" is used to tell the compiler that this variable may be changed in other places. So it's a good idea to add this for globals:

[tt]volatile unsigned char record_button_state;[/tt] (or)

[tt]volatile unsigned char record_button_state = 17;[/tt]

global export

Now we need to export the variable as global.

This is normally done in the header-file or above the declaration.

The global export may not initialize the value!

[tt]extern volatile unsigned char record_button_state;    // in myfile.h or on top of myfile.c

volatile unsigned char record_button_state = 17;      // in myfile.c[/tt]

note that this is not only valid for variables, but also for functions.

I hope this helps :)

best regards,

Michael

ps: As I'm an autodidact, I always welcome any corrections or better explanations :)

[robinfawell]

Thanks Michael

Here is the top of my revised applicaton c file.

      #include "cmios.h"

#include "pic18f452.h"

extern volatile unsigned char record_button_state;

void SendNote(unsigned char chn, unsigned char note, unsigned int velocity);

void SendTremelo();

void SendDump(unsigned char dump_index);

void SendPedalNotes(unsigned char pin, unsigned char pin_value);

//void WriteMem ( unsigned char q, unsigned char pin);

  // void Memory_IO(unsigned int start_addr);

unsigned char SetLed_NoDump(unsigned char low_pin, unsigned char high_pin, unsigned char canc_pin, unsigned char stored_pin, unsigned char pin, unsigned char pin_value );

unsigned char SetLed_SendDump(unsigned char low_pin, unsigned char high_pin, unsigned char canc_pin, unsigned char stored_pin, unsigned char pin, unsigned char pin_value ); //void RecordSetup ();

//void Set_Mem_Led_Rec_1 ( unsigned char value, unsigned int flag_addr, unsigned char pin, unsigned char pin_value);//used when Record is set

unsigned char dump_index; //triggers sysex messages

//unsigned char memory_group_rec_1 [6];

volatile unsigned char record_button_state = 17;//Record Pin 16

unsigned char k;// used to "count" flag memory locations

unsigned char q;

unsigned int addr;

I have tried to follow your suggestions but the record_button_state remains at 0.

Please note that there are two entries at line 3 and the 15th line.  Is this what you intended?

Thanks for spending your time in helping me.

Robin

[TK.]

I think, that the initialisation of RAM variables outside a function won't work, because this requires a special SDCC specific copy routine, which copies the value from flash memory into RAM.

It's located here:

http://sdcc.svn.sourceforge.net/viewvc/sdcc/trunk/sdcc/device/lib/pic16/startup/crt0i.c?revision=3714&view=markup

but I never tried it out.

An easier (and sometimes less code consuming) way is to initialize global variables inside the Init() Hook of MIOS

Best Regards, Thorsten.

[robinfawell]

Dear Thorsten

I am nearing the end of the organ project ( I hope!) and found that there was a problem in starting the organ in a common sense way.  In fact to select any organ stops it was necessary to push either the "Record" or "Playback" button first.

This was not logical.

I decided to see if I could initialise the variable to the  "non Record" "non Playback" state (7).  I knew that if I could achieve this, the organ would start by selecting an organ stop.

and made the following entry in the void Init(void) function

play_rec_group_stored_pin = 7;

It worked !

Many Thanks again.  Robin