//*****************************************************************************
//  MSP-FET430P140 Demo - USART0, Ultra-Low Pwr UART 19200 Echo ISR, 32kHz ACLK
//
//  Description: Echo a received character, USART0 RX ISR at high-speed used
//  with ultra-low power techniques. Normal operation in LPM3, Set_DCO
//  subroutine needs to be called to configure DCO that is used for UART baud
//  generation. On valid RX character, character echoed back. Use start-bit
//  edge detect - URXSE - to automatically (re)enable DCO and trigger ISR. ISR
//  must make sure DCO clock source remains enabled for the UART to receive
//  full character.
//  Software needs to make sure a character has been completely TX'ed, or RX'ed
//  before entering LPM3, which disables DCO required for the USART baud rate
//  generator. In the example, TX'ing is checked using the TXEPT bit directly.
//  RX'ing is checked using the SSEL0 clock select bit as a flag. This is
//  possible because UCLK0 = SMCLK when either both SSEL1 and SSEL0 or just
//  SSEL1 = 1. In the example, when SSEL1 = SSEL0 = 1 there is no RX'ing, and
//  LPM3 is allowed. When SSEL 1 = 1 and  SSEL0 = 0 SMCLK is selected, but
//  RX'ing is active and the DCO is required, thus LPM3 is not allowed.
//  ACLK = LFXT1/8 = 32768/8,  MCLK = SMCLK = UCLK0 = DCOCLK = 1048576
//  Baud rate divider with 1048576hz= 1048576Hz/19200 ~ 55 (0036h)
//  //* An external 32kHz watch crystal on XIN XOUT is required for ACLK *//	
//
//
//                MSP430F149
//             -----------------
//         /|\|              XIN|-
//          | |                 | 32768Hz
//          --|RST          XOUT|-
//            |                 |
//            |             P3.4|------------>
//            |                 | 19200 - 8N1
//            |             P3.5|<------------
//
//
//  M. Buccini
//  Texas Instruments Inc.
//  Feb 2005
//  Built with IAR Embedded Workbench Version: 3.21A
//*****************************************************************************

#include  <msp430x14x.h>

void Set_DCO (void);

void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT
  P3SEL |= 0x30;                            // P3.4,5 = USART0 TXD/RXD
  BCSCTL1 |= DIVA_3;                        // ACLK= LFXT1CLK/8
  Set_DCO();                                // Set DCO

  ME1 |= UTXE0 + URXE0;                     // Enabled USART0 TXD/RXD
  UCTL0 |= CHAR;                            // 8-bit character, SWRST = 1
  UTCTL0 |= SSEL1 + SSEL0 + URXSE;          // UCLK = SMCLK, start edge detect
  UBR00 = 0x36;                             // 19200 from 1Mhz
  UBR10 = 0x00;
  UMCTL0 = 0x6B;                            // Modulation
  UCTL0 &= ~SWRST;                          // Initialize USART state machine
  IE1 |= URXIE0;                            // Enable USART0 RX interrupt

  for (;;)
  {
    while (!(UTCTL0 & TXEPT));              // Confirm no TXing before --> LPM3
    _DINT();                                // Disable interrupts for flag test
    _NOP();
    if (!(UTCTL0 & SSEL0))
       _BIS_SR(LPM0_bits + GIE);            // RX'ing char, enter LPM0, int's active
    else
    _BIS_SR(LPM3_bits + GIE);               // Enter LPM3, int's active
  }
}

#pragma vector=UART0RX_VECTOR
__interrupt void usart0_rx (void)
{
  if ((IFG1 & URXIFG0))                     // Test URXIFG0
  {
    while (!(IFG1 & UTXIFG0));              // USART0 TX buffer ready?
    TXBUF0 = RXBUF0;                        // RXBUF0 to TXBUF0
    _BIC_SR_IRQ(LPM3_bits);                 // Exit LPM3 after reti
    UTCTL0 |= SSEL0;                        // SSEL0 = 1, no RX activity
  }
  else                                      // Start edge
  {
    UTCTL0 &= ~URXSE;                       // Clear URXS signal
    UTCTL0 |= URXSE;                        // Re-enable edge detect
    _BIC_SR_IRQ(SCG1 + SCG0);               // DCO reamins on after reti
    UTCTL0 &= ~SSEL0;                       // SSEL0= 0, RX activity
  }
}

//------------------------------------------------------------------------------
void Set_DCO (void)                         // Set DCO to selected frequency
//------------------------------------------------------------------------------
{
#define DELTA 256                           // Target DCO = DELTA*(4096) = 1048576

  unsigned int Compare, Oldcapture = 0;

  CCTL2 = CM_1 + CCIS_1 + CAP;              // CAP, ACLK
  TACTL = TASSEL_2 + MC_2 + TACLR;          // SMCLK, cont-mode, clear

  while (1)
  {
    while (!(CCIFG & CCTL2));               // Wait until capture occured
    CCTL2 &= ~CCIFG;                        // Capture occured, clear flag
    Compare = CCR2;                         // Get current captured SMCLK
    Compare = Compare - Oldcapture;         // SMCLK difference
    Oldcapture = CCR2;                      // Save current captured SMCLK
    if (DELTA == Compare) break;            // If equal, leave "while(1)"

    else if (DELTA < Compare)
    {
      DCOCTL--;
      if (DCOCTL == 0xFF)                   // DCO is too fast, slow it down
      {
        if (!(BCSCTL1 == (XT2OFF + DIVA_3)))
        BCSCTL1--;                          // Did DCO role under?, Sel lower RSEL
      }
    }
    else
    {
      DCOCTL++;                             // DCO is too slow, speed it down
      if (DCOCTL == 0x00)
      {
        if (!(BCSCTL1 == (XT2OFF + DIVA_3 + 0x07)))
        BCSCTL1++;                          // Did DCO role over? Sel higher RSEL
      }
    }
  }

  CCTL2 = 0;                                // Stop CCR2
  TACTL = 0;                                // Stop Timer_A
}