ws281x driver using USCI SPI, with updated asm code for msp430-elf-gcc

main.cpp

/*
 * main.cpp - msp430-elf-gcc ws281x USCI SPI driver using inline asm
 *
 *  Author: kimballr
 *  Date: Dec 28, 2012
 *  Version: 0.0002
 *
 * 2014-09-29 rrk - updated for both msp430-elf-gcc and msp430-gcc
 * P1.0 - CS - N/A not used, however it is still useful as an oscilloscope trigger
 * P1.7 - MOSI -> WS281x DIN
 */

#include <msp430.h>
#include <stdint.h>

typedef  struct {
  uint8_t g;
  uint8_t r;
  uint8_t b;
} RGBLED;

#define DATA_OUT_PIN BIT7 /* MOSI */

/* macro to switch from RBG->GRB */
#define RGB(x) ((unsigned long)(x)>>8)&0xff, ((unsigned long)(x)>>16)&0xff, (x)&0xff

static inline
void sendRGB(uint8_t * led_data, unsigned led_data_len);

int main(void) {
  WDTCTL = WDTPW | WDTHOLD;
  
  P1DIR |= BIT4; P1SEL |= BIT4;
  P1DIR |= BIT0; P1OUT &= ~BIT0;

  BCSCTL1 = CALBC1_16MHZ;
  DCOCTL = CALDCO_16MHZ;
  __delay_cycles(128);
  DCOCTL = (DCOCTL+32) & (0b11100000); // set to next non-modulated value > 16MHz

  __delay_cycles(8000000);

  // configure USCI B0 as 800kHz per bit
  UCB0CTL1 = UCSWRST;   // put in reset mode
  UCB0CTL0 = (UCMST | UCSYNC | UCMSB); // 8-bit SPI Master, MSB first data 
  P1SEL |= DATA_OUT_PIN;
  P1SEL2 |= DATA_OUT_PIN;
  UCB0CTL1 = UCSSEL_2;  // SMCLK and take out of reset mode

#if 1 /* goofing around */
  __asm__ __volatile("mov #3, %[UCB0BR]" : : [UCB0BR] "m" (UCB0BR0));
#else
  UCB0BR0  = 0x03;       // 1/(16MHz/3) = ~0.1875us per bit
  UCB0BR1  = 0;
#endif
  UCB0CTL1 &= ~UCSWRST;

  {
    static const uint8_t pixel_data[] = {
      RGB(0x0F0000),    // red - all colors at 50%
      RGB(0x000F00),    // green
      RGB(0x00000F),    // blue
      0x0F, 0x0F, 0x0F, // white
      0x00, 0x0F, 0x00, // red
      0x0F, 0x00, 0x00, // green
      0x00, 0x00, 0x0F, // blue
    };
    unsigned color_indx=0;

    while(1) {
      __delay_cycles(16000000/2);
      P1OUT ^= BIT0; // toggle CS
#if 1
      sendRGB((uint8_t *) &pixel_data[color_indx], 12); // target 4 leds*(24 bit color)
      color_indx = ( color_indx == 9 ) ? 0 : color_indx += 3;
#else
      static const uint8_t test_leds[] = {
	0b10110011, 0b00001111, 0b11110000
      };
      sendRGB(const_cast<uint8_t *>(test_leds), 3);
#endif
      P1OUT ^= BIT0;
    }

  };
  return 0;
}

#if 0
/*
 * straight c version
 */
void sendRGB(uint8_t * led_data, unsigned led_data_len) {
  uint8_t *colorbits = &led_data[0];

  do {
    unsigned color = *colorbits++;
    unsigned colorpixel = 0x80; // shift out bits in MSB order

    do {
      while (!(IFG2 & UCB0TXIFG)); // wait for the tx buffer to be empty
      (color & colorpixel) ? (UCB0TXBUF = 0xF0) : (UCB0TXBUF = 0xC0);
      colorpixel >>= 1;
    } while (colorpixel);
  } while (--led_data_len);

  while(UCB0STAT & UCBUSY); // wait for all bits to be transmitted

  //__delay_cycles(800); // delay 50us to latch data, not be necessary as main loop waits 
}

#else

/*
 * inline msp430-elf-gcc asm version
 */
void sendRGB(uint8_t * led_data, unsigned led_data_len) {
  unsigned color, bit_cnt;

  // shift out bits in MSB order
  __asm__ __volatile__
     (
      "1:\n"
        " mov.b @%[led_data]+, %[color]   ; 2 cycles\n"
        " mov.b #8, %[bit_cnt]            ; 1 cycle\n"
        "2:\n"
          " and.b %[TXIFG], %[IFG2]       ; 4 cycles\n"
          " jz    2b                      ; 2 cycles\n"
          " rlc.b %[color]                ; 1 cycle\n"
          " jc 3f                         ; 2 cycles\n"
          " mov.b %[OFF_BITS], %[TXBUF]   ; 4 cycles\n"
          " jmp 4f                        ; 2 cycles\n"
          "3:\n"
          " mov.b %[ON_BITS], %[TXBUF]    ; 4 cycles\n"
          " jmp .+2                       ; 2 cycles\n"
          "4:\n"
          " dec %[bit_cnt]                ; 1 cycle\n"
          " jnz 2b                        ; 2 cycles\n"
        " dec %[led_data_len]             ; 1 cycle\n"
        " jnz 1b                          ; 2 cycles\n"
      "5:\n"
        " and.b %[UCBUSY_], %[STAT]       ; 4 cycles\n" 
        " jnz 5b                          ; 2 cycles\n"

      :[led_data]      "+&r" (led_data)
       ,[led_data_len] "+&r" (led_data_len)
       ,[color]        "=&r" (color)
       ,[bit_cnt]      "=&r" (bit_cnt)
       
      :[ON_BITS]     "r" (0b11110000)
       ,[OFF_BITS]   "r" (0b11000000)
       ,[TXBUF]      "m" (UCB0TXBUF)
       ,[IFG2]       "m" (IFG2)
       ,[STAT]       "m" (UCB0STAT)
       ,[TXIFG]      "i" (UCB0TXIFG)
       ,[UCBUSY_]    "i" (UCBUSY)

      : "cc"

      );

  // NOTE: caller must delay 50us to latch data
}
#endif