Quick Start Guide for AC - Basic

In this use case, the Analog Comparator module is configured for:

• Comparator peripheral in manually triggered (e.g. "Single Shot" mode)
• One comparator channel connected to input MUX pin 0 and compared to a scaled V_CC/2 voltage

This use case sets up the Analog Comparator to compare an input voltage fed into a GPIO pin of the device against a scaled voltage of the microcontroller's V_CC power rail. The comparisons are made on-demand in single-shot mode, and the result stored into a local variable which is then output to the board LED to visually show the comparison state.

Setup

Prerequisites

There are no special setup requirements for this use-case.

Code

Copy-paste the following setup code to your user application:

/* AC module software instance (must not go out of scope while in use) */
static struct ac_module ac_instance;

/* Comparator channel that will be used */
#define AC_COMPARATOR_CHANNEL   AC_CHAN_CHANNEL_0

void configure_ac(void)
{
    /* Create a new configuration structure for the Analog Comparator settings
     * and fill with the default module settings. */
    struct ac_config config_ac;
    ac_get_config_defaults(&config_ac);

    /* Alter any Analog Comparator configuration settings here if required */

    /* Initialize and enable the Analog Comparator with the user settings */
    ac_init(&ac_instance, AC, &config_ac);
}

void configure_ac_channel(void)
{
    /* Create a new configuration structure for the Analog Comparator channel
     * settings and fill with the default module channel settings. */
    struct ac_chan_config ac_chan_conf;
    ac_chan_get_config_defaults(&ac_chan_conf);

    /* Set the Analog Comparator channel configuration settings */
    ac_chan_conf.sample_mode      = AC_CHAN_MODE_SINGLE_SHOT;
    #if (SAMR30E)
        ac_chan_conf.positive_input   = AC_CHAN_POS_MUX_PIN2;
    #else
        ac_chan_conf.positive_input   = AC_CHAN_POS_MUX_PIN0;
    #endif
    
    ac_chan_conf.negative_input   = AC_CHAN_NEG_MUX_SCALED_VCC;
    ac_chan_conf.vcc_scale_factor = 32;

    /* Set up a pin as an AC channel input */
    struct system_pinmux_config ac0_pin_conf;
    system_pinmux_get_config_defaults(&ac0_pin_conf);
    ac0_pin_conf.direction    = SYSTEM_PINMUX_PIN_DIR_INPUT;
    ac0_pin_conf.mux_position = CONF_AC_MUX;
    system_pinmux_pin_set_config(CONF_AC_PIN, &ac0_pin_conf);

    /* Initialize and enable the Analog Comparator channel with the user
     * settings */
    ac_chan_set_config(&ac_instance, AC_COMPARATOR_CHANNEL, &ac_chan_conf);
    ac_chan_enable(&ac_instance, AC_COMPARATOR_CHANNEL);
}

Add to user application initialization (typically the start of main()):

    system_init();
    configure_ac();
    configure_ac_channel();
    ac_enable(&ac_instance);

Workflow

1. Create an AC device instance struct, which will be associated with an Analog Comparator peripheral hardware instance.

   static struct ac_module ac_instance;

   Note

   Device instance structures shall never go out of scope when in use.

2. Define a macro to select the comparator channel that will be sampled, for convenience.

   #define AC_COMPARATOR_CHANNEL   AC_CHAN_CHANNEL_0

3. Create a new function configure_ac(), which will be used to configure the overall Analog Comparator peripheral.

   void configure_ac(void)

4. Create an Analog Comparator peripheral configuration structure that will be filled out to set the module configuration.

       struct ac_config config_ac;

5. Fill the Analog Comparator peripheral configuration structure with the default module configuration values.

       ac_get_config_defaults(&config_ac);

6. Initialize the Analog Comparator peripheral and associate it with the software instance structure that was defined previously.

       ac_init(&ac_instance, AC, &config_ac);

7. Create a new function configure_ac_channel(), which will be used to configure the overall Analog Comparator peripheral.

   void configure_ac_channel(void)

8. Create an Analog Comparator channel configuration structure that will be filled out to set the channel configuration.

       struct ac_chan_config ac_chan_conf;

9. Fill the Analog Comparator channel configuration structure with the default channel configuration values.

       ac_chan_get_config_defaults(&ac_chan_conf);

10. Alter the channel configuration parameters to set the channel to one-shot mode, with the correct negative and positive MUX selections and the desired voltage scaler.

        ac_chan_conf.sample_mode      = AC_CHAN_MODE_SINGLE_SHOT;
        #if (SAMR30E)
            ac_chan_conf.positive_input   = AC_CHAN_POS_MUX_PIN2;
        #else
            ac_chan_conf.positive_input   = AC_CHAN_POS_MUX_PIN0;
        #endif
        
        ac_chan_conf.negative_input   = AC_CHAN_NEG_MUX_SCALED_VCC;
        ac_chan_conf.vcc_scale_factor = 32;

    Note

    The voltage scalar formula is documented in description for ac_chan_config::vcc_scale_factor.

11. Configure the physical pin that will be routed to the AC module channel 0.

        struct system_pinmux_config ac0_pin_conf;
        system_pinmux_get_config_defaults(&ac0_pin_conf);
        ac0_pin_conf.direction    = SYSTEM_PINMUX_PIN_DIR_INPUT;
        ac0_pin_conf.mux_position = CONF_AC_MUX;
        system_pinmux_pin_set_config(CONF_AC_PIN, &ac0_pin_conf);

12. Initialize the Analog Comparator channel and configure it with the desired settings.

        ac_chan_set_config(&ac_instance, AC_COMPARATOR_CHANNEL, &ac_chan_conf);

13. Enable the now initialized Analog Comparator channel.

        ac_chan_enable(&ac_instance, AC_COMPARATOR_CHANNEL);

14. Enable the now initialized Analog Comparator peripheral.

        ac_enable(&ac_instance);

Implementation

Code

Copy-paste the following code to your user application:

    ac_chan_trigger_single_shot(&ac_instance, AC_COMPARATOR_CHANNEL);

    uint8_t last_comparison = AC_CHAN_STATUS_UNKNOWN;

    while (true) {
        if (ac_chan_is_ready(&ac_instance, AC_COMPARATOR_CHANNEL)) {
            do {
                last_comparison = ac_chan_get_status(&ac_instance,
                        AC_COMPARATOR_CHANNEL);
            } while (last_comparison & AC_CHAN_STATUS_UNKNOWN);

            port_pin_set_output_level(LED_0_PIN,
                    (last_comparison & AC_CHAN_STATUS_NEG_ABOVE_POS));

            ac_chan_trigger_single_shot(&ac_instance, AC_COMPARATOR_CHANNEL);
        }
    }

Workflow

1. Trigger the first comparison on the comparator channel.

       ac_chan_trigger_single_shot(&ac_instance, AC_COMPARATOR_CHANNEL);

2. Create a local variable to maintain the current comparator state. Since no comparison has taken place, it is initialized to AC_CHAN_STATUS_UNKNOWN.

       uint8_t last_comparison = AC_CHAN_STATUS_UNKNOWN;

3. Make the application loop infinitely, while performing triggered comparisons.

       while (true) {

4. Check if the comparator is ready for the last triggered comparison result to be read.

           if (ac_chan_is_ready(&ac_instance, AC_COMPARATOR_CHANNEL)) {

5. Read the comparator output state into the local variable for application use, re-trying until the comparison state is ready.

               do {
                   last_comparison = ac_chan_get_status(&ac_instance,
                           AC_COMPARATOR_CHANNEL);
               } while (last_comparison & AC_CHAN_STATUS_UNKNOWN);

6. Set the board LED state to mirror the last comparison state.

               port_pin_set_output_level(LED_0_PIN,
                       (last_comparison & AC_CHAN_STATUS_NEG_ABOVE_POS));

7. Trigger the next conversion on the Analog Comparator channel.

               ac_chan_trigger_single_shot(&ac_instance, AC_COMPARATOR_CHANNEL);