hal_adc.c

/**************************************************************************************************
  Filename:       hal_adc.c
  Revised:        $Date: 2010-07-06 15:24:36 -0700 (Tue, 06 Jul 2010) $
  Revision:       $Revision: 22897 $

  Description:    This file contains the interface to the HAL ADC.


  Copyright 2006-2010 Texas Instruments Incorporated. All rights reserved.

  IMPORTANT: Your use of this Software is limited to those specific rights
  granted under the terms of a software license agreement between the user
  who downloaded the software, his/her employer (which must be your employer)
  and Texas Instruments Incorporated (the "License").  You may not use this
  Software unless you agree to abide by the terms of the License. The License
  limits your use, and you acknowledge, that the Software may not be modified,
  copied or distributed unless embedded on a Texas Instruments microcontroller
  or used solely and exclusively in conjunction with a Texas Instruments radio
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  works of, modify, distribute, perform, display or sell this Software and/or
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  YOU FURTHER ACKNOWLEDGE AND AGREE THAT THE SOFTWARE AND DOCUMENTATION ARE
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**************************************************************************************************/

/**************************************************************************************************
 *                                           INCLUDES
 **************************************************************************************************/

#include  "hal_adc.h"
#include  "hal_defs.h"
#include  "hal_mcu.h"
#include  "hal_types.h"

/**************************************************************************************************
 *                                            CONSTANTS
 **************************************************************************************************/
#define HAL_ADC_EOC         0x80    /* End of Conversion bit */
#define HAL_ADC_START       0x40    /* Starts Conversion */

#define HAL_ADC_STSEL_EXT   0x00    /* External Trigger */
#define HAL_ADC_STSEL_FULL  0x10    /* Full Speed, No Trigger */
#define HAL_ADC_STSEL_T1C0  0x20    /* Timer1, Channel 0 Compare Event Trigger */
#define HAL_ADC_STSEL_ST    0x30    /* ADCCON1.ST =1 Trigger */

#define HAL_ADC_RAND_NORM   0x00    /* Normal Operation */
#define HAL_ADC_RAND_LFSR   0x04    /* Clock LFSR */
#define HAL_ADC_RAND_SEED   0x08    /* Seed Modulator */
#define HAL_ADC_RAND_STOP   0x0c    /* Stop Random Generator */
#define HAL_ADC_RAND_BITS   0x0c    /* Bits [3:2] */

#define HAL_ADC_DEC_064     0x00    /* Decimate by 64 : 8-bit resolution */
#define HAL_ADC_DEC_128     0x10    /* Decimate by 128 : 10-bit resolution */
#define HAL_ADC_DEC_256     0x20    /* Decimate by 256 : 12-bit resolution */
#define HAL_ADC_DEC_512     0x30    /* Decimate by 512 : 14-bit resolution */
#define HAL_ADC_DEC_BITS    0x30    /* Bits [5:4] */

#define HAL_ADC_STSEL       HAL_ADC_STSEL_ST
#define HAL_ADC_RAND_GEN    HAL_ADC_RAND_STOP
#define HAL_ADC_REF_VOLT    HAL_ADC_REF_AVDD
#define HAL_ADC_DEC_RATE    HAL_ADC_DEC_064
#define HAL_ADC_SCHN        HAL_ADC_CHN_VDD3
#define HAL_ADC_ECHN        HAL_ADC_CHN_GND

/* ------------------------------------------------------------------------------------------------
 *                                       Local Variables
 * ------------------------------------------------------------------------------------------------
 */

#if (HAL_ADC == TRUE)
static uint8 adcRef;
#endif

/**************************************************************************************************
 * @fn      HalAdcInit
 *
 * @brief   Initialize ADC Service
 *
 * @param   None
 *
 * @return  None
 **************************************************************************************************/
void HalAdcInit (void)
{
#if (HAL_ADC == TRUE)
  adcRef = HAL_ADC_REF_VOLT;
#endif
}

/**************************************************************************************************
 * @fn      HalAdcRead
 *
 * @brief   Read the ADC based on given channel and resolution
 *
 * @param   channel - channel where ADC will be read
 * @param   resolution - the resolution of the value
 *
 * @return  16 bit value of the ADC in offset binary format.
 *
 *          Note that the ADC is "bipolar", which means the GND (0V) level is mid-scale.
 *          
 **************************************************************************************************/
uint16 HalAdcRead (uint8 channel, uint8 resolution)
{
  int16  reading = 0;

#if (HAL_ADC == TRUE)
  uint8   i, resbits;
  uint8  adcChannel = 1;

  /*
   * If Analog input channel is AIN0..AIN7, make sure corresponing P0 I/O pin is enabled.  The code
   * does NOT disable the pin at the end of this function.  I think it is better to leave the pin
   * enabled because the results will be more accurate.  Because of the inherent capacitance on the
   * pin, it takes time for the voltage on the pin to charge up to its steady-state level.  If
   * HalAdcRead() has to turn on the pin for every conversion, the results may show a lower voltage
   * than actuality because the pin did not have time to fully charge.
   */
  if (channel < 8)
  {
    for (i=0; i < channel; i++)
    {
      adcChannel <<= 1;
    }
  }

  /* Enable channel */
  ADCCFG |= adcChannel;

  /* Convert resolution to decimation rate */
  switch (resolution)
  {
    case HAL_ADC_RESOLUTION_8:
      resbits = HAL_ADC_DEC_064;
      break;
    case HAL_ADC_RESOLUTION_10:
      resbits = HAL_ADC_DEC_128;
      break;
    case HAL_ADC_RESOLUTION_12:
      resbits = HAL_ADC_DEC_256;
      break;
    case HAL_ADC_RESOLUTION_14:
    default:
      resbits = HAL_ADC_DEC_512;
      break;
  }

  /* writing to this register starts the extra conversion */
  ADCCON3 = channel | resbits | adcRef;

  /* Wait for the conversion to be done */
  while (!(ADCCON1 & HAL_ADC_EOC));

  /* The following would disable channel after done conversion */
  // JHP - HOWEVER, we find that this lets the 2541 drive the
  // pin a bit, which we don't find desirable for our application
  // ADCCFG &= (adcChannel ^ 0xFF);

  /* Read the result */
  reading = (int16) (ADCL);
  reading |= (int16) (ADCH << 8);

  /* Treat small negative as 0 */
  if (reading < 0)
    reading = 0;

  switch (resolution)
  {
    case HAL_ADC_RESOLUTION_8:
      reading >>= 8;
      break;
    case HAL_ADC_RESOLUTION_10:
      reading >>= 6;
      break;
    case HAL_ADC_RESOLUTION_12:
      reading >>= 4;
      break;
    case HAL_ADC_RESOLUTION_14:
    default:
      reading >>= 2;
    break;
  }
#else
  // unused arguments
  (void) channel;
  (void) resolution;
#endif

  return ((uint16)reading);
}

/**************************************************************************************************
 * @fn      HalAdcSetReference
 *
 * @brief   Sets the reference voltage for the ADC and initializes the service
 *
 * @param   reference - the reference voltage to be used by the ADC
 *
 * @return  none
 *
 **************************************************************************************************/
void HalAdcSetReference ( uint8 reference )
{
#if (HAL_ADC == TRUE)
  adcRef = reference;
#endif
}

/*********************************************************************
 * @fn      HalAdcCheckVdd
 *
 * @brief   Check for minimum Vdd specified.
 *
 * @param   vdd - The board-specific Vdd reading to check for.
 *
 * @return  TRUE if the Vdd measured is greater than the 'vdd' minimum parameter;
 *          FALSE if not.
 *
 *********************************************************************/
bool HalAdcCheckVdd(uint8 vdd)
{
  ADCCON3 = 0x0F;
  while (!(ADCCON1 & 0x80));
  return (ADCH > vdd);
}

/**************************************************************************************************
**************************************************************************************************/