//******************************************************************************
//   MSP430xG46x Demo - USCI_A0, SPI 3-Wire Slave Data Echo
//
//   Description: SPI slave talks to SPI master using 3-wire mode. Data received
//   from master is echoed back.  USCI RX ISR is used to handle communication,
//   CPU normally in LPM4.  Prior to initial data exchange, master pulses
//   slaves RST for complete reset.
//   ACLK = 32.768kHz, MCLK = SMCLK = DCO ~ 1048kHz
//
//   Use with SPI Master Incremented Data code example.  If the slave is in
//   debug mode, the reset signal from the master will conflict with slave's
//   JTAG; to work around, use IAR's "Release JTAG on Go" on slave device.  If
//   breakpoints are set in slave RX ISR, master must stopped also to avoid
//   overrunning slave RXBUF.
//
//                MSP430FG4619
//             -----------------
//         /|\|              XIN|-
//          | |                 |   32kHz xtal
//          | |             XOUT|-
// Master---+-|RST              |
//            |             P7.1|<- Data In (UCA0SIMO)
//            |                 |
//            |             P7.2|-> Data Out (UCA0SOMI)
//            |                 |
//            |             P7.3|<- Serial Clock In (UCA0CLK)
//
//
//   K. Quiring/ M. Mitchell
//   Texas Instruments Inc.
//   October 2006
//   Built with IAR Embedded Workbench Version: 3.41A
//******************************************************************************
#include  <msp430xG46x.h>


void main(void)
{
  volatile unsigned int i;

  WDTCTL = WDTPW+WDTHOLD;                   // Stop watchdog timer
  FLL_CTL0 |= XCAP14PF;                     // Configure load caps

  // Wait for xtal to stabilize
  do
  {
  IFG1 &= ~OFIFG;                           // Clear OSCFault flag
  for (i = 0x47FF; i > 0; i--);             // Time for flag to set
  }
  while ((IFG1 & OFIFG));                   // OSCFault flag still set?

  for(i=2100;i>0;i--);                      // Now with stable ACLK, wait for
                                            // DCO to stabilize.
  while(!(P7IN&0x08));                      // If clock sig from mstr stays low,
                                            // it is not yet in SPI mode
  P7SEL |= 0x00E;                           // P7.3,2,1 option select
  UCA0CTL1 = UCSWRST;                       // **Put state machine in reset**
  UCA0CTL0 |= UCSYNC+UCCKPL+UCMSB;          //3-pin, 8-bit SPI master
  UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
  IE2 |= UCA0RXIE;                          // Enable USCI_A0 RX interrupt

  _BIS_SR(LPM4_bits + GIE);                 // Enter LPM4, enable interrupts
}

// Echo character
#pragma vector=USCIAB0RX_VECTOR
__interrupt void USCIA0RX_ISR (void)
{
  while (!(IFG2 & UCA0TXIFG));              // USCI_A0 TX buffer ready?
  UCA0TXBUF = UCA0RXBUF;
}