An Analog to Digital Converter (ADC) is a device that translates an analog voltage to a digital value that a microprocessor can understand.

The ConnectCore platforms have several ADC interfaces. You can find more information inHardware reference manualsandAnalog-to-Digital Converter (ADC).

Digi adds an API to Linux for managing these ADC interfaces. To use this API, include the following header file in your application:

#include

Request an ADC

You can request an ADC with one of the following functions:

Function Description

adc_t *ldx_adc_request(unsigned int adc_chip, unsigned int adc_channel)

Requests an ADC by its chip number and channel number.

It returns a pointer toadc_ton success,NULLon error.

adc_t *ldx_adc_request_by_alias(char const * const adc_alias)

Requests an ADC by its alias name. The ADC alias mapping must be defined in the/etc/libdigiapix.conffile under the[ADC]section. SeeEstablish ADC aliases.

It returns a pointer toadc_ton success,NULLon error.
Requested ADCs must be freed once they are no longer used. SeeFree an ADC.

Both functions may fail and returnNULLfor the following reasons:

  • The provided chip and channel numbers cannot be exported.

  • The associated chip and channel numbers to the given aliases cannot be exported.

  • The API encountered problems allocating memory to initialize the ADC. Your system may have run out of resources.

Requesting an ADC
[...]/* Request an ADC using its alias */adc_t adc1 = ldx_adc_request_by_alias("DEFAULT_ADC");/* Request an ADC located in the chip = 0 channel = 1 */adc_t adc2 = ldx_adc_request (0,1); printf("The ADC 1 is on chip %d, channel %d\n", adc1->adc_chip, adc1->adc_channel); printf("The ADC 2 is on chip %d, channel %d\n", adc2->adc_chip, adc2->adc_channel); [...]

Establish ADC aliases

To help you identify the ADCs in your design, you can assign aliases to your ADC Linux IDs. Map the assigned chip number, channel, and name in the/etc/libdigiapix.conffile:

  1. Add a section called[ADC], if one doesn’t already exist.

  2. Below the section name, add the list of mapped ADCs following the format:

     = ,

    Where:

    • is the human-readable name for the ADC.

    • is the ADC chip.

    • is the ADC channel used by that ADC chip.

Example of ADC section
[ADC]# ADC1_IN2 on GPIO board connector (pin 13)DEFAULT_ADC=0, 2

For example, using the configuration above, you can request an ADC with the API usingDEFAULT_ADCalias. SeeRequest an ADC.

You can use these functions to get the chip and the channel associated with an alias:

intldx_adc_get_chip(constchar*constadc_alias)
intldx_adc_get_channel(constchar*constadc_alias)
For more information about how to includelibdigiapix.confin your Digi Embedded Yocto images, seeDefine interface aliases.

Free an ADC

You must free a requested ADC when it is no longer required. To do so, use theldx_adc_free()function.

intldx_adc_free(adc_t *adc)
Freeing a requested ADC
[...] adc_t *adc = ...; [...]/* Free ADC once it is not required anymore */ldx_adc_free(adc); [...]

Read ADC samples

Synchronous read

You can read an ADC sample using this function:

Function Description

int ldx_adc_get_sample (adc_t * adc)

Retrieves the value of the ADC channel. It returns a value between 0-4096 (depending of the input voltage). If there is an error, -1 is returned.

For more information, seeAnalog-to-Digital Converter (ADC).
Read ADC value
[...] adc_t *adc = ...;intsample =0; [...]/* Read the adc value */sample = ldx_adc_get_sample(adc); printf("Input ADC sample acquired: %d", sample); [...]

Asynchronous read

You can configure an ADC channel to perform asynchronous sample reads using a defined time interval. To do so, use the non-blockingldx_adc_start_sampling()function.

int ldx_adc_start_sampling(adc_t *adc, const ldx_adc_read_cb_t read_cb, unsigned int interval, void *arg)

This function registers the specified callback handler to be executed when the sample interval is finished and a sample is read. After that, it continues sampling each time the interval expires.

argis passed as an argument ofldx_adc_read_cb_tcallback.

ldx_adc_start_sampling()returns:

  • EXIT_SUCCESS on success.

  • EXIT_FAILURE when failing:

    • If the ADC doesn’t exist.

    • If there is a problem allocating memory.

The provided callback must follow this prototype:

typedefint(*ldx_adc_read_cb_t)(intsample,void*arg)

To stop the asynchronous samples read, useldx_adc_stop_sampling().

intldx_adc_stop_sampling(adc_t *adc)
Use continuous sampling
/* Sample read callback */staticintadc_sampling_cb(intsample,void*arg) {int* tmp_count = (int*) arg; *tmp_count = *tmp_count +1; printf("Input ADC sample acquired: %d in loop: %d\n", sample, tmp_count);returnEXIT_SUCCESS; } [...]intsamples_count =0;intsampling_interval_sec =10; adc_t *adc = ldx_adc_request_by_alias("MY_ADC"); [...]/* Start ADC sampling */ldx_adc_start_sampling(adc, &adc_sampling_cb, sampling_interval_sec , &samples_count);do{ printf("Number of samples obtained: %d\n", samples_count");sleep(1): }while(samples_count <10); [...]/* Stop sampling */ldx_adc_stop_sampling(adc); [...]

Convert ADC value into millivolts

By default, the ADC samples are read in raw mode. You can convert the raw read into millivolts using theldx_adc_convert_sample_to_mv()function:

Function Description

int ldx_adc_convert_sample_to_mv(adc_t *adc, int sample)

Scale the sample to convert the value to mV. Returns -1 if there is an error.

For more information, seeAnalog-to-Digital Converter (ADC).

The driver automatically reads the scale applied to the raw sample in order to convert the value into millivolts. You can use theldx_set_scale()function to change the scaling factor:

intldx_set_scale(adc_t *adc,floatscale)
Configure ADC scale
[...] adc_t *adc = ...;floatscale_raw_to_mv =0.805;// 3300 mV --> 4095 rawintsample; [...]/* Configure ADC scale value */ldx_adc_set_scale(adc, scale_raw_to_mv); sample = ldx_adc_get_sample(adc); sample = ldx_adc_convert_sample_to_mv(adc, sample); printf("The voltage in the ADC chip %d, channel %d is %dmV\n", adc->chip, adc->channel, sample); [...]

ADC example

In this example, you can select an ADC to get periodic samples of the channel.

You can import the example in Eclipse using the Digi Embedded Yocto plugin. For more information, seeCreate a new DEY sample project. This example is included in Digi Embedded Yocto. Go toGitHubto see the application source code.