This driver provides an interface for the megaAVR ADC module.

It consists of inline functions that can be used to configure the ADC module and blocking ADC read functions for both 8- and 10-bit results.

Interface

To initialize the ADC you can use the adc_init() function. This sets the ADC prescaler and enables the ADC module. These operations can also be done separately using the adc_set_prescaler() and adc_enable() functions.

To do a blocking ADC read there are two different functions, one for 8-bit and one for 10-bit results:

adc_read_8bit() : return an 8-bit result
adc_read_10bit() : return a 10-bit result

Usage

First include the header file:

#include "adc.h"

Then initialize and enable the ADC with the correct prescaler:

adc_init(ADC_PRESCALER_DIV32);

To do an 8-bit read of ADC channel 0 using 1.1V internal reference:

analog_val = adc_read_8bit(ADC_MUX_ADC0, ADC_VREF_1V1);

The syntax to do a 10-bit read is the same, but it returns a 16-bit unsigned integer to fit the whole 10-bit result.

analog_val = adc_read_10bit(ADC_MUX_ADC0, ADC_VREF_1V1);

the adc_read_8bit() and adc_read_10bit() functions do not take into account the fact that the voltage reference may be unstable after changing it. It is recommended to discard the first sample after changing voltage reference to avoid incorrect results.

Note: None of the functions are interrupt safe to avoid overhead. If you need interrupt protection you can use the following in your application code:
irqflags_t flags = cpu_irq_save();

adc_set_mux(ADC_MUX_ADC0);

cpu_irq_restore(flags);

Macros
#define	ADC_ADTS_SOURCE_MASK (1 << ADTS2 \| 1 << ADTS1 \| 1 << ADTS0)

#define	ADC_MUX_MASK (1 << MUX3 \| 1 << MUX2 \| 1 << MUX1 \| 1 << MUX0)

#define	ADC_PRESCALER_MASK (1 << ADPS2 \| 1 << ADPS1 \| 1 << ADPS0)

#define	ADC_VREF_MASK (1 << REFS1 \| 1 << REFS0)

Enumerations
enum	adc_adjustment { ADC_ADJUSTMENT_RIGHT = 0, ADC_ADJUSTMENT_LEFT = (1 << ADLAR) }

enum	adc_auto_trigger_source { ADC_AUTOTRIGGER_SOURCE_FREERUNNING = (0x0 << ADTS0), ADC_AUTOTRIGGER_SOURCE_ANALOG_COMPARATOR = (0x1 << ADTS0), ADC_AUTOTRIGGER_SOURCE_EIR0 = (0x2 << ADTS0), ADC_AUTOTRIGGER_SOURCE_TC0_COMPARE = (0x3 << ADTS0), ADC_AUTOTRIGGER_SOURCE_TC0_OVERFLOW = (0x4 << ADTS0), ADC_AUTOTRIGGER_SOURCE_TC1_COMPARE_B = (0x5 << ADTS0), ADC_AUTOTRIGGER_SOURCE_TC1_OVERFLOW = (0x6 << ADTS0), ADC_AUTOTRIGGER_SOURCE_TC1_CAPTURE = (0x7 << ADTS0) }
	ADC Auto Trigger sources. More...

enum	adc_mux_setting { ADC_MUX_ADC0 = 0x0, ADC_MUX_ADC1 = 0x1, ADC_MUX_ADC2 = 0x2, ADC_MUX_ADC3 = 0x3, ADC_MUX_ADC4 = 0x4, ADC_MUX_ADC5 = 0x5, ADC_MUX_ADC6 = 0x6, ADC_MUX_ADC7 = 0x7, ADC_MUX_1V1 = 0x1E, ADC_MUX_GND = 0x1F, ADC_MUX_ADC0_ADC0_10X = 0x8, ADC_MUX_ADC1_ADC0_10X = 0x9, ADC_MUX_ADC0_ADC0_200X = 0xA, ADC_MUX_ADC1_ADC0_200X = 0xB, ADC_MUX_ADC2_ADC2_10X = 0xC, ADC_MUX_ADC3_ADC2_10X = 0xD, ADC_MUX_ADC2_ADC2_200X = 0xE, ADC_MUX_ADC3_ADC2_200X = 0xF, ADC_MUX_ADC0_ADC1 = 0x10, ADC_MUX_ADC1_ADC1 = 0x11, ADC_MUX_ADC2_ADC1 = 0x12, ADC_MUX_ADC3_ADC1 = 0x13, ADC_MUX_ADC4_ADC1 = 0x14, ADC_MUX_ADC5_ADC1 = 0x15, ADC_MUX_ADC6_ADC1 = 0x16, ADC_MUX_ADC7_ADC1 = 0x17, ADC_MUX_ADC0_ADC2 = 0x18, ADC_MUX_ADC1_ADC2 = 0x19, ADC_MUX_ADC2_ADC2 = 0x1A, ADC_MUX_ADC3_ADC2 = 0x1B, ADC_MUX_ADC4_ADC2 = 0x1C, ADC_MUX_ADC5_ADC2 = 0x1D }
	ADC input MUX settings. More...

enum	adc_prescaler { ADC_PRESCALER_DIV2 = (0x1 << ADPS0), ADC_PRESCALER_DIV4 = (0x2 << ADPS0), ADC_PRESCALER_DIV8 = (0x3 << ADPS0), ADC_PRESCALER_DIV16 = (0x4 << ADPS0), ADC_PRESCALER_DIV32 = (0x5 << ADPS0), ADC_PRESCALER_DIV64 = (0x6 << ADPS0), ADC_PRESCALER_DIV128 = (0x7 << ADPS0) }
	ADC prescaler settings. More...

enum	adc_voltage_reference { ADC_VREF_AREF = (0x0 << REFS0), ADC_VREF_AVCC = (0x1 << REFS0), ADC_VREF_1V1 = (0x2 << REFS0), ADC_VREF_2V56 = (0x3 << REFS0) }
	ADC voltage references. More...

Functions
static bool	adc_conversion_is_complete (void)
	Poll ADC conversion complete interrupt flag. More...

static void	adc_disable (void)

static void	adc_disable_autotrigger (void)

static void	adc_disable_interrupt (void)

static void	adc_enable (void)

static void	adc_enable_autotrigger (void)

static void	adc_enable_interrupt (void)

static uint16_t	adc_get_data_10bit (void)

static uint8_t	adc_get_data_8bit (void)

static void	adc_init (enum adc_prescaler prescaler)
	ADC initialization. More...

static uint16_t	adc_read_10bit (enum adc_mux_setting input, enum adc_voltage_reference vref)
	Blocking ADC conversion with 10-bit result. More...

static uint8_t	adc_read_8bit (enum adc_mux_setting input, enum adc_voltage_reference vref)
	Blocking ADC conversion with 8-bit result. More...

static void	adc_set_autotrigger_source (enum adc_auto_trigger_source trg)
	Set ADC Auto Trigger source. More...

static void	adc_set_mux (enum adc_mux_setting input)
	Select source from ADC input mux. More...

static void	adc_set_prescaler (enum adc_prescaler prescaler)
	Set ADC clock prescaler. More...

static void	adc_set_voltage_reference (enum adc_voltage_reference vref)
	Set the ADC voltage reference. More...

static void	adc_start_conversion (void)

Optimized functions for register accesses
These functions are for cases where you do not want the overhead of masking out bitfields before updating the register value. These will only do a write to the register instead of a read-modify-write.
static void	adc_set_admux (uint8_t regval)
	Set voltage reference, mux and adjustment bits in admux register. More...

#define ADC_ADTS_SOURCE_MASK (1 << ADTS2 | 1 << ADTS1 | 1 << ADTS0)

Referenced by adc_set_autotrigger_source().

#define ADC_MUX_MASK (1 << MUX3 | 1 << MUX2 | 1 << MUX1 | 1 << MUX0)

Referenced by adc_read_10bit(), adc_read_8bit(), and adc_set_mux().

#define ADC_PRESCALER_MASK (1 << ADPS2 | 1 << ADPS1 | 1 << ADPS0)

Referenced by adc_set_prescaler().

#define ADC_VREF_MASK (1 << REFS1 | 1 << REFS0)

Referenced by adc_set_voltage_reference().

enum adc_adjustment

Enumerator
ADC_ADJUSTMENT_RIGHT
ADC_ADJUSTMENT_LEFT

enum adc_auto_trigger_source

ADC Auto Trigger sources.

Available trigger sources for ADC Auto Trigger

Enumerator
ADC_AUTOTRIGGER_SOURCE_FREERUNNING
ADC_AUTOTRIGGER_SOURCE_ANALOG_COMPARATOR
ADC_AUTOTRIGGER_SOURCE_EIR0
ADC_AUTOTRIGGER_SOURCE_TC0_COMPARE
ADC_AUTOTRIGGER_SOURCE_TC0_OVERFLOW
ADC_AUTOTRIGGER_SOURCE_TC1_COMPARE_B
ADC_AUTOTRIGGER_SOURCE_TC1_OVERFLOW
ADC_AUTOTRIGGER_SOURCE_TC1_CAPTURE

enum adc_mux_setting

ADC input MUX settings.

MUX settings for ADC input

Note: If using 10X or 200X gain only 2.56V should be used as internal voltage reference.; The doxygen documentation contains MUX settings for multiple devices. check the device datasheet or family header files to find what options are available on your device.

Enumerator
ADC_MUX_ADC0	ADC0, single ended.
ADC_MUX_ADC1	ADC1, single ended.
ADC_MUX_ADC2	ADC2, single ended.
ADC_MUX_ADC3	ADC3, single ended.
ADC_MUX_ADC4	ADC4, single ended.
ADC_MUX_ADC5	ADC5, single ended.
ADC_MUX_ADC6	ADC6, single ended.
ADC_MUX_ADC7	ADC7, single ended.
ADC_MUX_1V1	1.1V internal bandgap voltage
ADC_MUX_GND	GND, single ended.
ADC_MUX_ADC0_ADC0_10X	Positive: ADC0 Negative: ADC0 Gain: 10x.
ADC_MUX_ADC1_ADC0_10X	Positive: ADC1 Negative: ADC0 Gain: 10x.
ADC_MUX_ADC0_ADC0_200X	Positive: ADC0 Negative: ADC0 Gain: 200x.
ADC_MUX_ADC1_ADC0_200X	Positive: ADC1 Negative: ADC0 Gain: 200x.
ADC_MUX_ADC2_ADC2_10X	Positive: ADC2 Negative: ADC2 Gain: 10x.
ADC_MUX_ADC3_ADC2_10X	Positive: ADC3 Negative: ADC2 Gain: 10x.
ADC_MUX_ADC2_ADC2_200X	Positive: ADC2 Negative: ADC2 Gain: 200x.
ADC_MUX_ADC3_ADC2_200X	Positive: ADC3 Negative: ADC2 Gain: 200x.
ADC_MUX_ADC0_ADC1	Positive: ADC0 Negative: ADC1.
ADC_MUX_ADC1_ADC1	Positive: ADC1 Negative: ADC1.
ADC_MUX_ADC2_ADC1	Positive: ADC2 Negative: ADC1.
ADC_MUX_ADC3_ADC1	Positive: ADC3 Negative: ADC1.
ADC_MUX_ADC4_ADC1	Positive: ADC4 Negative: ADC1.
ADC_MUX_ADC5_ADC1	Positive: ADC5 Negative: ADC1.
ADC_MUX_ADC6_ADC1	Positive: ADC6 Negative: ADC1.
ADC_MUX_ADC7_ADC1	Positive: ADC7 Negative: ADC1.
ADC_MUX_ADC0_ADC2	Positive: ADC0 Negative: ADC2.
ADC_MUX_ADC1_ADC2	Positive: ADC1 Negative: ADC2.
ADC_MUX_ADC2_ADC2	Positive: ADC2 Negative: ADC2.
ADC_MUX_ADC3_ADC2	Positive: ADC3 Negative: ADC2.
ADC_MUX_ADC4_ADC2	Positive: ADC4 Negative: ADC2.
ADC_MUX_ADC5_ADC2	Positive: ADC5 Negative: ADC2.

enum adc_prescaler

ADC prescaler settings.

Available ADC prescaler settings

Enumerator
ADC_PRESCALER_DIV2
ADC_PRESCALER_DIV4
ADC_PRESCALER_DIV8
ADC_PRESCALER_DIV16
ADC_PRESCALER_DIV32
ADC_PRESCALER_DIV64
ADC_PRESCALER_DIV128

enum adc_voltage_reference

ADC voltage references.

Available ADC voltage references

Enumerator
ADC_VREF_AREF	AREF, internal Vref turned off.
ADC_VREF_AVCC	AVCC.
ADC_VREF_1V1	Internal 1.1V voltage reference.
ADC_VREF_2V56	Internal 2.56V voltage reference.

static bool adc_conversion_is_complete ( void )

inlinestatic

Poll ADC conversion complete interrupt flag.

Returns: false if conversion not complete

static void adc_disable ( void )

inlinestatic

static void adc_disable_autotrigger ( void )

inlinestatic

static void adc_disable_interrupt ( void )

inlinestatic

static void adc_enable ( void )

inlinestatic

static void adc_enable_autotrigger ( void )

inlinestatic

static void adc_enable_interrupt ( void )

inlinestatic

static uint16_t adc_get_data_10bit ( void )

inlinestatic

static uint8_t adc_get_data_8bit ( void )

inlinestatic

static void adc_init ( enum adc_prescaler prescaler )

inlinestatic

ADC initialization.

Set ADC prescaler and enable the ADC

Parameters

prescaler ADC clock prescaler

Referenced by main().

static uint16_t adc_read_10bit	(	enum adc_mux_setting	input,
		enum adc_voltage_reference	vref
	)

inlinestatic

Blocking ADC conversion with 10-bit result.

An example demonstrating the minimum initialization needed to perform a conversion:

// Initialize and enable ADC
adc_init(ADC_PRESCALER_DIV64);
analog_val = adc_read_10bit(ADC_MUX_ADC0, ADC_VREF_1V1);

Parameters

input	ADC input mux selection and voltage reference
vref	ADC voltage reference

Returns: Conversion result as an unsigned 16-bit integer

Note: The first ADC conversion result after switching reference voltage source may be inaccurate, and the user is advised to discard this result. this function is not interrupt safe

References ADC_MUX_MASK.

static uint8_t adc_read_8bit	(	enum adc_mux_setting	input,
		enum adc_voltage_reference	vref
	)

inlinestatic

Blocking ADC conversion with 8-bit result.

An example demonstrating the minimum initialization needed to perform a conversion:

// Initialize ADC
adc_init(ADC_PRESCALER_DIV32);
analog_val = adc_read_8bit(ADC_MUX_ADC0, ADC_VREF_1V1);

Parameters

input	ADC input mux selection.
vref	ADC voltage reference

Returns: Conversion result as an unsigned 8-bit integer

Note: The first ADC conversion result after switching reference voltage source may be inaccurate, and the user is advised to discard this result. this function is not interrupt safe.

References ADC_ADJUSTMENT_LEFT, and ADC_MUX_MASK.

Referenced by main().

static void adc_set_admux ( uint8_t regval )

inlinestatic

Set voltage reference, mux and adjustment bits in admux register.