mcp48x2_dac.c

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/**
 * @file mcp48x2_dac.c
 * @ingroup mcp48x2
 * @author Jason Duffy
 * @date 4th March 2022
 * @brief Driver for the MCP4812 10 bit DAC (digital to analog converter) chip.
 * @bug No known bugs. 
 * @details This file provides the basic low-level functionality for the
 * MCP4812 10 bit DAC from Microchip. This driver currently only allows for a
 * single DAC to be used, but this might be improved on at a later date. This
 * driver was written using the datasheet for the Microchip MCP4812 chip, which
 * can be found at the link below.
 * @see https://ww1.microchip.com/downloads/en/DeviceDoc/20002249B.pdf
 */
 
#include <util/delay.h>
#include <avr/interrupt.h>
 
#include "mcp48x2_dac.h"
#include "atmega_spi.h"
#include "pin_defines.h"
 
// Bit positions for configuration. 
#define CHANNEL_BIT              15U
#define GAIN_BIT                 13U
#define SHUTDOWN_BIT             12U
 
// Offset values for setting raw level value. 
#define TWELVE_BIT_LEVEL_OFFSET  0U
#define TEN_BIT_LEVEL_OFFSET     2U
#define EIGHT_BIT_LEVEL_OFFSET   4U
 
// Offset values for setting millivolts. 
#define TWELVE_BIT_MV_OFFSET     0U
#define TEN_BIT_MV_OFFSET        1U
#define EIGHT_BIT_MV_OFFSET      3U
 
/**
 * File scope copy of dac_config_t pointer to store address of config object.
 */
static dac_config_t *p_config_global;
 
/**
 * File scope variable to store the bitshift value to account for resolution
 * differences between chip models. 
 */
static uint8_t mv_resolution_shift = 0;
 
/**
 * File scope variable to store the bitshift value to account for resolution
 * differences between chip models. 
 */
static uint8_t level_resolution_shift = 0;
 
// Forward declarations of private helper functions.
void chip_select(void);
void chip_deselect(void);
 
 
/*
 * Initialisation routine (run once at startup).
 * This function is to be called before using any other DAC functions.
 * Instantiate the dac_config_t object first then pass it's address into and
 * call init_lcd() before using any other lcd functions.
 * @param p_config is a pointer to the dac_config_t object.
 */
void init_dac(dac_config_t *p_config)
{
    // Copy config object pointer to a variable with file scope. 
    p_config_global = p_config;
 
    // Delay to allow power ramp up in device.
    _delay_ms(500);
 
    // Initialise SPI comms. 
    init_spi(lsb_first,
             controller,
             rising_edge,
             sample_leading_edge,
             cpu_clk_div_16,
             single_speed);
 
    DAC_CTRL_DDR |= (1 << DAC_CS); // Set chip select as output.
    DAC_CTRL_PORT |= (1 << DAC_CS); // Set CS line high (not selected).
    DAC_CTRL_DDR |= (1 << LDAC); // Set LDAC line (latch) as output.
    DAC_CTRL_PORT |= (1 << LDAC); // Set LDAC high.
 
    // Save the value to bitshift millivolts value by. 
    if (p_config_global->model == mcp4802)
    {
      mv_resolution_shift = EIGHT_BIT_MV_OFFSET;
      level_resolution_shift = EIGHT_BIT_LEVEL_OFFSET;
    }
    else if (p_config_global->model == mcp4812)
    {
      mv_resolution_shift = TEN_BIT_MV_OFFSET;
      level_resolution_shift = TEN_BIT_LEVEL_OFFSET;
    }
    else
    {
      mv_resolution_shift = TWELVE_BIT_MV_OFFSET;
      level_resolution_shift = TWELVE_BIT_LEVEL_OFFSET;
    }  
 
    // Establish latching settings
    if (!p_config_global->sync_manually)
    {
      DAC_CTRL_PORT &= ~(1 << LDAC);
    }
 
    // Send new values to DAC
    dac_reconfigure();
}
 
 
/*
 * Sends a new millivolts value to be output on DAC (Along with config
 * settings). For 8 or 10 bit models only.
 * @param channel_a: true = Channel A, false = Channel B.
 * @param millivolts: mV value to be output by DAC. Ensure that this value
 * doesn't exceed the maxixum for the DAC model and gain setting. 
 */
void dac_set_voltage(bool channel_a, uint16_t millivolts)
{
    // Manipulate mv value to suit register size of chip and gain setting.
    if (channel_a)
    {
        if (p_config_global->channel_a.gain_low)
        {   
            p_config_global->channel_a.level =
                                (millivolts >> mv_resolution_shift);
        }
        else
        {
            p_config_global->channel_a.level =
                                (millivolts >> (mv_resolution_shift + 1));
        }
    }
    else
    {
        if (p_config_global->channel_b.gain_low)
        {
            p_config_global->channel_b.level =
                                (millivolts >> mv_resolution_shift);
        }
        else
        {
            p_config_global->channel_b.level =
                                (millivolts >> (mv_resolution_shift + 1));
        }
    }
 
    // Send new values to DAC
    dac_reconfigure();
}
 
 
/*
 * Sends a new millivolts value to be output on DAC (Along with config
 * settings). For 12 bit models only. 
 * @param channel_a: true = Channel A, false = Channel B.
 * @param millivolts: mV value to be output by DAC. Ensure that this value
 * doesn't exceed the maxixum for the DAC model and gain setting.
 * @param fractional: true = millivolts value has 0.5mV added to it. Only to be
 * used when gain_low is true. 
 */
void dac_set_voltage_12_bit(bool channel_a,
                            uint16_t millivolts,
                            bool fractional)
{
    if (channel_a)
    {
        if(p_config_global->channel_a.gain_low)
        {
            p_config_global->channel_a.level =
                                (millivolts << (TWELVE_BIT_MV_OFFSET + 1));
            // Add the 0.5mV value if required. 
            if (fractional == true)
            {
                p_config_global->channel_a.level += 1;
            }
        }
        else
        {
            p_config_global->channel_a.level =
                                (millivolts << TWELVE_BIT_MV_OFFSET);
        }
    }
    else
    {
        if(p_config_global->channel_b.gain_low)
        {
            p_config_global->channel_b.level =
                                (millivolts << (TWELVE_BIT_MV_OFFSET + 1));
            // Add the 0.5mV value if required. 
            if (fractional == true)
            {
                p_config_global->channel_b.level += 1;
            }
        }
        else
        {
            p_config_global->channel_b.level =
                                (millivolts << TWELVE_BIT_MV_OFFSET);
        }
    }
 
    // Send new values to DAC
    dac_reconfigure();
}
 
 
/*
 * Applies new config settings. This function takes updated config settings for
 * both channels of DAC, then re-sends data so that the new settings take
 * effect.
 */
void dac_reconfigure(void)
{
    uint16_t channel_a_data = 0;
    uint16_t channel_b_data = 0;
 
    // Set up config bits in 16bit word to be sent. 
    channel_a_data &= ~(1 << CHANNEL_BIT); // Clear channel bit (Channel A).
    channel_a_data |= (p_config_global->channel_a.gain_low << GAIN_BIT);
    channel_a_data |= (p_config_global->channel_a.active << SHUTDOWN_BIT);
 
    channel_b_data |= (1 << CHANNEL_BIT); // Set channel bit (Channel B).
    channel_b_data |= (p_config_global->channel_b.gain_low << GAIN_BIT);
    channel_b_data |= (p_config_global->channel_b.active << SHUTDOWN_BIT);
 
    // Shift level into correct place for chip and OR it into our 16bit word.
    channel_a_data |=
                (p_config_global->channel_a.level << level_resolution_shift);
 
    channel_b_data |=
                (p_config_global->channel_b.level << level_resolution_shift);
                
 
    // Send data for channel A to DAC over SPI. 
    chip_select();
    spi_trade_word(channel_a_data);
    chip_deselect();
 
    // Send data for channel B to DAC over SPI.
    chip_select();
    spi_trade_word(channel_b_data);
    chip_deselect();
 
    // If sync_manually is set to false, pulse LDAC to update values. 
    if (!p_config_global->sync_manually)
    {
        pulse_latch();
    }
}
 
 
/*
 * Pulses LDAC pin pow for 1 microsecond. If sync_manually = true, call this
 * function to latch the new voltage values into the output registers. If
 * sync_manually = false, this function is called automatically by
 * dac_reconfigure() or dac_set_voltage().
 */
void pulse_latch(void)
{
    DAC_CTRL_PORT &= ~(1 << LDAC);
    _delay_us(1);
    DAC_CTRL_PORT |= (1 << LDAC);
}
 
// ------------------------------------------------------------------------- //
// ------------------------ Private Helper Functions ----------------------- //
// ------------------------------------------------------------------------- // 
 
 
/**
 * Private helper function - pulls CS line (Chip Select) low in order to begin
 * SPI communication with DAC.
 */
void chip_select(void)
{
    DAC_CTRL_PORT &= ~(1 << DAC_CS);
}
 
/**
 * Private helper function - pulls CS line (Chip Select) high to signal the end
 * of SPI communication with DAC.
 */
void chip_deselect(void)
{
    DAC_CTRL_PORT |= (1 << DAC_CS);
}
 
 
/*** end of file ***/