Subversion Repositories svn.mios

Rev

Blame | Last modification | View Log | RSS feed

HEADER 3 MIOS C Example

<H3>Send CC Events on pot movements within specific range (Scaling)</H3>

<P CLASS=INFO>We want to send MIDI events on pot movements. In difference to <A HREF="mios_c_send_ain.html">this simple example</A>, the sent value is scaled to the given boundaries, the value range can be specified in a table.</P>

<P CLASS=INFO>Copy the SDCC skeleton into a new directory, open the main.c file and enhance the AIN_NotifyChange() function like shown below. Thereafter type "make" in the command shell, and upload the new project.hex file to the core.</P>

<TT><PRE>
// this const definition creates a table of 32 bytes in flash memory
// we create a 2-dimensional array with 8 entries
// each entry consists of four bytes: 
//   o one for the first MIDI byte (MIDI status)
//   o a second for the second MIDI byte (here: CC number)
//   o the minimum value
//   o the maximum value
// The meaning of the bytes can be found in the MIDI spec
// (-> http://www.borg.com/~jglatt/tech/midispec.htm)

const unsigned char pot_event_map[8][4] = {
// evt0  evt1   min   max
  {0xb0, 0x10, 0x00, 0x0f}, // Pot #1
  {0xb0, 0x11, 0x00, 0x1f}, // Pot #2
  {0xb0, 0x12, 0x00, 0x2f}, // Pot #3
  {0xb0, 0x13, 0x00, 0x3f}, // Pot #4
  {0xb0, 0x14, 0x00, 0x7f}, // Pot #5
  {0xb0, 0x15, 0x40, 0x7f}, // Pot #6
  {0xb0, 0x16, 0x30, 0x5f}, // Pot #7
  {0xb0, 0x17, 0x20, 0x6f}, // Pot #8
  };


/////////////////////////////////////////////////////////////////////////////
// This function is called by MIOS after startup to initialize the 
// application
/////////////////////////////////////////////////////////////////////////////
void Init(void) __wparam
{
  // initialize the AIN driver
  MIOS_AIN_NumberSet(8);   // 8 pots are connected
  MIOS_AIN_UnMuxed();      // the AINX4 modules are *not* used
  MIOS_AIN_DeadbandSet(7); // should be 7 when 7bit resolution is used
}

/////////////////////////////////////////////////////////////////////////////
// This is an assembly optimized function which scales a 7bit value between
// a minimum and maximum value
/////////////////////////////////////////////////////////////////////////////
unsigned char Scale_7bit(unsigned char value, unsigned char min, unsigned char max)
{
  // scaled value is (2*<7bit value> * <range>) >> 8
  PRODL = value << 1; // 8bit value
  PRODH = max-min+1;  // range
__asm
    movf _PRODL, W
    mulwf _PRODH, 0
__endasm;

  return min + PRODH;
}

/////////////////////////////////////////////////////////////////////////////
// This function is called by MIOS when a pot has been moved
/////////////////////////////////////////////////////////////////////////////
void AIN_NotifyChange(unsigned char pin, unsigned int pin_value) __wparam
{
  unsigned char value;

  // scale 7bit value between min and max boundary
  value = Scale_7bit(MIOS_AIN_Pin7bitGet(pin), // converted to 7bit
                     pot_event_map[pin][2],    // min value
                     pot_event_map[pin][3]);   // max value

  // send scaled CC value
  MIOS_MIDI_TxBufferPut(pot_event_map[pin][0]); // first value from table
  MIOS_MIDI_TxBufferPut(pot_event_map[pin][1]); // second value from table
  MIOS_MIDI_TxBufferPut(value);                 // scaled pot value
}
</PRE></TT>

<P CLASS=INFO>A list of available MIOS functions can be found <A HREF="cmios_fun.html">here</A>.</P>

FOOTER