zoom/firmware/dac.c

#include "config.h"
#include "dac.h"

/* Initialize DAC (AD5542) */
void dac_init(void)
{
	/* SPI2 */
	IEC2bits.SPI2IE = 0;

	SPI2CON1bits.DISSCK = 0;
	SPI2CON1bits.DISSDO = 0;
	SPI2CON1bits.MODE16 = 1;
	SPI2CON1bits.SMP = 0;
	SPI2CON1bits.CKE = 0;
	SPI2CON1bits.SSEN = 0;
	SPI2CON1bits.CKP = IO_HIGH;
	SPI2CON1bits.MSTEN = 1;
	SPI2CON1bits.SPRE = 4;
	SPI2CON1bits.PPRE = 3;

	/* There's no framed mode that does the normal
       "chip select" behavior, so control /SS2 manually */
	SPI2CON2bits.FRMEN = 0;
	LATGbits.LATG9 = IO_HIGH;
	TRISGbits.TRISG9 = 0;

	SPI2STATbits.SPISIDL = 0;
	SPI2STATbits.SPIEN = 1;

	dac_write(0x0000);
}

static const uint16_t dac_lookup[1024] = {
  #include "lookup.inc"
};

/* Write raw 16-bit desired value to DAC:
   DAC_HIGH 4.9998v
   DAC_MID  0v
   DAC_LOW -5v
 */
void dac_write(uint16_t val)
{
	LATGbits.LATG9 = IO_LOW;
	if (IO_HIGH == 1)
		SPI2BUF = __dac_to_spi_cmd(val);
	else
		SPI2BUF = ~__dac_to_spi_cmd(val);
	while (!SPI2STATbits.SPIRBF)
		continue;
	(void) SPI2BUF;
	LATGbits.LATG9 = IO_HIGH;
}

/* Given a DAC command between DAC_LOW and DAC_HIGH,
   get the actual expected output voltage as a 16-bit value, where:
     0xffff = 4.9998v
     0x8000 = 0v
     0x0000 = -5v
*/
uint16_t dac_get_actual_16bit(uint16_t val)
{
	return __dac_to_16bit_equiv(val);
}

/* Given a DAC command between DAC_LOW and DAC_HIGH,
   get the actual expected output voltage as a FLOAT, where:
     DAC_HIGH = 4.9998v
     DAC_MID  = 0v
     DAC_LOW  = -5v
   Example: for 10-bit DAC, convert integer command 123 into
   the more accurate 123.45 using known lower bits.
*/
float dac_get_actual_float(uint16_t val)
{
	return __dac_to_16bit_equiv(val) * (DAC_RANGE / 65536.0);
}