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Altera_Forum's avatar
Altera_Forum
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14 years ago

alt_getchar returning wrong value

int main()
{ 
  int noia = 0;
  alt_putstr("Proc 2!\n");
  /* get the mutex device handle */
  alt_mutex_dev* mutex = altera_avalon_mutex_open( "/dev/mutex" );
  /* acquire the mutex, setting the value to one */
  altera_avalon_mutex_lock( mutex, 1 );
  if(altera_avalon_mutex_is_mine(mutex))
    {
      alt_printf("%x\n", IORD_32DIRECT(SHARED_MEM_BASE, 0x00));
      noia = alt_getchar();
      alt_printf("%x\n", noia);
        if (noia == 1)
          altera_avalon_mutex_unlock( mutex );
    }
  return 0;
}

This is my code, however alt_getchar() is returning a wrong value, not what i typed

5 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    Hi, Are you new to C programs ?

    Your printf will print hexadecimal value. because of "%x"

    try 

    
      noia = alt_getchar();
      alt_printf("%c\n", noia);

    But later in your code I see 
    if (noia == 1)
    !

    If you type with keyboard, alt_getchar may return between 40 and 124 (decimal values).

    So if you want you condition to be true you have to Press Alt with 0 then 0 then 1.

    If you want your condition to be true when you type '1' with keyboard, try 

    if (noia == '1')

    noia should be declared as char (not "int").

    Or this is an other problem.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    It's another problem, seems like my buffer has already some info on it. I don't type anything and some value appear in the alt_getchar, like 1a, 2b etc.

    Thanks for your info thought :)
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Be aware that alt_getchar() uses a "direct" driver. See Documents.

    Have you tried with C usual getchar() ?
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    I'd guess that the result range of alt_getchar() is -1 (no char available) and 0..255 for a received byte (it could also return indications of abort and framing errors) - so the return value could well be 'int' not 'char'.

    getchar() will pull in a lot of libc code, and may also (by default at least) require that you type <enter> before making any data available.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    --- Quote Start ---

    It's another problem, seems like my buffer has already some info on it. I don't type anything and some value appear in the alt_getchar, like 1a, 2b etc.

    Thanks for your info thought :)

    --- Quote End ---

    If your problem is simply with chars already stored in buffer, what you commonly do in C is putting a while (getchar() != EOF); loop before starting.

    EOF is usually the portable version of the -1 result value suggested by dsl.