// Make sure the Timer can produce the appropriate frequency in 8-bit mode
// Supported SMBus Frequencies range from 10kHz to 100kHz.  The CKCON register
// settings may need to change for frequencies outside this range.
#if ((SYSCLK/SMB_FREQUENCY/3) < 255)
   #define SCALE 1
      CKCON |= 0x08;                   // Timer1 clock source = SYSCLK
#elif ((SYSCLK/SMB_FREQUENCY/4/3) < 255)
   #define SCALE 4
      CKCON |= 0x01;
      CKCON &= ~0x0A;                  // Timer1 clock source = SYSCLK / 4
#endif

   TMOD = 0x20;                        // Timer1 in 8-bit auto-reload mode

   // Timer1 configured to overflow at 1/3 the rate defined by SMB_FREQUENCY
   TH1 = -(SYSCLK/SMB_FREQUENCY/SCALE/3);

   TL1 = TH1;                          // Init Timer1

   TR1 = 1;                            // Timer1 enabled
}

//-----------------------------------------------------------------------------
// Timer3_Init()
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// Timer3 configured for use by the SMBus low timeout detect feature as
// follows:
// - Timer3 in 16-bit auto-reload mode
// - SYSCLK/12 as Timer3 clock source
// - Timer3 reload registers loaded for a 25ms overflow period
// - Timer3 pre-loaded to overflow after 25ms
// - Timer3 enabled
//
void Timer3_Init (void)
{
   TMR3CN = 0x00;                      // Timer3 configured for 16-bit auto-
                                       // reload, low-byte interrupt disabled

   CKCON &= ~0x40;                     // Timer3 uses SYSCLK/12

   TMR3RL = -(SYSCLK/12/40);           // Timer3 configured to overflow after
   TMR3 = TMR3RL;                      // ~25ms (for SMBus low timeout detect):
                                       // 1/.025 = 40

   EIE1 |= 0x80;                       // Timer3 interrupt enable
   TMR3CN |= 0x04;                     // Start Timer3
}

//-----------------------------------------------------------------------------
// PORT_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// Configure the Crossbar and GPIO ports.
//
// P0.0   digital   open-drain    SMBus SDA
// P0.1   digital   open-drain    SMBus SCL
//
// P3.3   digital   push-pull     LED
//
// all other port pins unused
//
void PORT_Init (void)
{
   P0MDOUT = 0x00;                     // All P0 pins open-drain output

   P3MDOUT |= 0x08;                    // Make the LED (P3.3) a push-pull
                                       // output

   XBR0 = 0x04;                        // Enable SMBus pins
   XBR1 = 0x40;                        // Enable crossbar and weak pull-ups

   P0 = 0xFF;
}

//-----------------------------------------------------------------------------
// Interrupt Service Routines
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
// SMBus Interrupt Service Routine (ISR)
//-----------------------------------------------------------------------------
//
// SMBus ISR state machine
// - Slave only implementation - no master states defined
// - All incoming data is written to global variable <SMB_data_IN>
// - All outgoing data is read from global variable <SMB_data_OUT>
//
void SMBus_ISR (void) interrupt 7
{
   static unsigned char sent_byte_counter;
   static unsigned char rec_byte_counter;

   if (ARBLOST == 0)
   {
      switch (SMB0CN & 0xF0)           // Decode the SMBus status vector
      {
         // Slave Receiver: Start+Address received
         case  SMB_SRADD:

            STA = 0;                   // Clear STA bit

            sent_byte_counter = 1;     // Reinitialize the data counters
            rec_byte_counter = 1;

            if((SMB0DAT&0xFE) == (SLAVE_ADDR&0xFE)) // Decode address
            {                          // If the received address matches,
               ACK = 1;                // ACK the received slave address

               if((SMB0DAT&0x01) == READ) // If the transfer is a master READ,
               {
                  // Prepare outgoing byte
                  SMB0DAT = SMB_DATA_OUT[sent_byte_counter-1];
                  sent_byte_counter++;
               }
            }
            else                       // If received slave address does not
            {                          // match,
               ACK = 0;                // NACK received address
            }
            break;

         // Slave Receiver: Data received
         case  SMB_SRDB:

            if (rec_byte_counter < NUM_BYTES_WR)
            {
               // Store incoming data
               SMB_DATA_IN[rec_byte_counter-1] = SMB0DAT;
               rec_byte_counter++;

               ACK = 1;                // ACK received data
            }
            else
            {
               // Store incoming data
               SMB_DATA_IN[rec_byte_counter-1] = SMB0DAT;

               DATA_READY = 1;         // Indicate new data fully received
               ACK = 1;                // ACK received data
            }

            break;

         // Slave Receiver: Stop received while either a Slave Receiver or
         // Slave Transmitter
         case  SMB_SRSTO:

            STO = 0;                   // STO must be cleared by software when
                                       // a STOP is detected as a slave
            break;

         // Slave Transmitter: Data byte transmitted
         case  SMB_STDB:

            if (ACK == 1)              // If Master ACK's, send the next byte
            {
               if (sent_byte_counter <= NUM_BYTES_RD)
               {
                  // Prepare next outgoing byte
                  SMB0DAT = SMB_DATA_OUT[sent_byte_counter-1];
                  sent_byte_counter++;
               }
            }                          // Otherwise, do nothing
            break;

         // Slave Transmitter: Arbitration lost, Stop detected
         //
         // This state will only be entered on a bus error condition.
         // In normal operation, the slave is no longer sending data or has
         // data pending when a STOP is received from the master, so the TXMODE
         // bit is cleared and the slave goes to the SRSTO state.
         case  SMB_STSTO:

            STO = 0;                   // STO must be cleared by software when
                                       // a STOP is detected as a slave
            break;

         // Default: all other cases undefined
         default:

            SMB0CF &= ~0x80;           // Reset communication
            SMB0CF |= 0x80;
            STA = 0;
            STO = 0;
            ACK = 0;
            break;
      }
   }
   // ARBLOST = 1, Abort failed transfer
   else
   {
      STA = 0;
      STO = 0;
      ACK = 0;
   }

   SI = 0;                             // Clear SMBus interrupt flag
}

//-----------------------------------------------------------------------------
// Timer3 Interrupt Service Routine (ISR)
//-----------------------------------------------------------------------------
//
// A Timer3 interrupt indicates an SMBus SCL low timeout.
// The SMBus is disabled and re-enabled here
//
void Timer3_ISR (void) interrupt 14
{
   SMB0CF &= ~0x80;                    // Disable SMBus
   SMB0CF |= 0x80;                     // Re-enable SMBus
   TMR3CN &= ~0x80;                    // Clear Timer3 interrupt-pending flag
}

//-----------------------------------------------------------------------------
// End Of File
//-----------------------------------------------------------------------------