cpux_04.c

Extended Memory Access Using IAR v3.42A and CCE v2

//******************************************************************************
//  MSP430xG461x Demo - R4 ptr, Rpt'd Blk to DAC0, Sine Out, TimerA0, DCO
//
// This program shows how register R4 can be locked to store a 20-bit address 
// variable to access the data look-up table placed in the extended memory, to
// transfer the contents in the data table word by word to the DAC.
//
// Description: A 32 word Sine look-up table is stored in the extended memory 
// location 0x10000 onwards by interfacing C with assembly code. Register R4 is 
// used as a pointer to store the 20-bit address of the extended memory.  
// ASM functions are provided to read and write the 20-bit address from/to 
// register R4. The R4 pointer is used to access the data from the extended 
// memory and transfer the contents of the Sine look-up table word-by-word as a 
// repeating block to DAC12_0. And DAC12_0 outputs on P6.6 a 1-kHz Sine wave. 
// Timer A operates in compare mode, where, TACCR0 sets Clk period and TACCR1 
// sets PWM duty cycle. To get a 1-kHz Sine wave out, timer period is set to 
// almost 32us (as 32us*32 words ~ 1ms) , with TimerA clock  running at 1MHz. 
// And during the TimerA0 ISR the data present at the address pointed by 
// register R4, is loaded to the DAC12_0 data reg and the contents of R4 are 
// incremented to point the next address. DAC12_0 uses internal 1.5V reference.
// ACLK = 32kHz, MCLK = SMCLK = default DCO 8MHz, TACLK = SMCLK/8 = 1MHZ
//
//                MSP430xG461x
//             -----------------
//         /|\|              XIN|-
//          | |                 | 32kHz
//          --|RST          XOUT|-
//            |                 |
//            |        DAC0/P6.6|--> ~ 1-kHz sine wave output
//
//   Note 1: The linker file for this project has to be modified to create a 
//           new memory segment(CONST_HIGH with memory range [10000 to 1FFFF] in
//           this example). The linker command -Z(CONST)CONST_HIGH=10000-1FFFF
//           is used to create a new memory segment in the extended memory 
//           (0x10000 - 0x1FFFF).
//   Note 2: This code example interfaces C with Assembler code, therefore, the 
//           project must include assembly file "ASM_func.s43".
//   Note 3: Register R4 is used as a address variable by the user and should be 
//           locked so that the compiler doesnt use this register for its   
//           operations. Therefore, the compiler commnd line option --lock_r4 is
//           to be used.
//           Project>Options>C/C++ Compiler>Code>R4 utilization>Not used      
//
//   Bhargavi Nisarga
//   Texas Instruments Inc.
//   June 2007
//   Built with IAR Embedded Workbench Version: 3.42A
//******************************************************************************

#include "msp430xG46x.h"
#include "intrinsics.h"

// Function prototypes for ASM functions
extern unsigned long __Get_Address20(void); 
extern void __Write_R4(unsigned long value);
extern unsigned int __Read_at_R4_plus(void);

unsigned short Count, Size;

void main(void)
{
  volatile unsigned int i;
  WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer
  
  //Set DCO freq = 8MHz
  FLL_CTL0 |= DCOPLUS + XCAP18PF;           // DCO+ set, freq = xtal x D x N+1
  SCFI0 |= FN_4;                            // x2 DCO freq, 8MHz nominal DCO
  SCFQCTL = 121;            
  
  ADC12CTL0 = REFON;                        // Internal 1.5V reference
  for (i = 0x3600; i; i--);                 // Delay for needed ref start-up.
                                            // See datasheet for details.
  
  // Initialize Pointer - R4 used as a pointer
  __Write_R4(__Get_Address20()); // Call ASM func to write 
                                            // starting address of data table in
                                            // extended memory to R4
  Size = 0x0020;                             //Size in words 
  Count = 0;  
  
  // Configur DAC12_0  
  DAC12_0CTL = DAC12IR + DAC12AMP_5 + DAC12ENC;
                                            // amp and i/p range setting, 
                                            // DAC enable  
  
  // Configure Timer A
  TACCTL1 = OUTMOD_3;                       // TACCR1 set/reset 
  TACCR1 = 1;                               // TACCR1 PWM Duty Cycle
  TACCR0 = 30;                              // Clock period of TACCR0
  TACCTL0 = CCIE;                           // Interrupt enable
  TACTL = TASSEL_2 + MC_1 + TACLR + ID_3;   // SMCLK, upmode, (i/p clk/8)
  
  __bis_SR_register(LPM0_bits + GIE);       // Enter LPM0, enable interrupts
}

// TimerA interrupt service routine
#pragma vector = TIMERA0_VECTOR
__interrupt void TA0_ISR(void)
{
  // Get data at the address present in R4 to DAC data reg and incr ptr  
  DAC12_0DAT = __Read_at_R4_plus(); 
  if (++Count >= Size)                      // Chk if count within memory range
  {
    // Repeat Block transfer from extended memory to DAC12_0
    __Write_R4(__Get_Address20()); 
    Count = 0;
  }
}