AD7490 no-OS driver

See drivers/adc/ad7490 (doxygen) for the Doxygen documentation.

Supported Devices

Overview

The AD7490 is a 12-bit high speed, low power, 16-channel, successive approximation ADC. The part operates from a single 2.7 V to 5.25 V power supply and features throughput rates up to 1 MSPS. The part contains a low noise, wide bandwidth track-and-hold amplifier that can handle input frequencies in excess of 1 MHz.

Applications

Multichannel system monitoring
Battery-powered equipment
Power line monitoring
Data acquisition, instrumentation, and process control

AD7490 Device Configuration

Driver Initialization

In order to be able to use the device, you will have to provide the support for the communication protocol (SPI).

The first API to be called is ad7490_init. Make sure that it returns 0, which means that the driver was initialized correctly.

Operation Mode Configuration

AD7490 has a total of 4 operation modes:

Normal Mode
Full Shutdown Mode
Auto Shutdown Mode
Auto Standby Mode

By using the ad7490_set_op_mode API, one can configure the AD7490 to work using the requested operation mode.

General Configuration

Other configurations such as range can be either REFIN (2.5V) or double the REFIN (5V), and coding wich can be either twos complement or binary can be configured by using ad7490_config API. Also the state of the DOUT pin is also controlled using the same API.

AD7490 Device Measurements

Single Channel Readings

By using the ad7490_read_ch API, a single channel can be read, and the output value is the raw value of the channel.

Multiple Channel Readings

Multiple channels can be read at once by using the sequencer, which can be started by using the ad7490_start_seq API, where either a shadow, control or consecutive type of sequencer cand be configured. (Please refer to the datasheet for each type of sequencer).

More to this, the type of sequencer can be changed without stopping the sequence by using ad7490_change_seq API, or stopped by using the ad7490_stop_seq. API.

After starting the sequencer, in order to read the channel values, one should use the ad7490_read_seq API which handles all the required operations related to the sequencer and returning all requested channel values in their ascending index order.

AD7490 Driver Initialization Example

struct ad7490_desc *ad7490;
struct ad7490_init_param ad7490_ip = {
        .spi_param =  {
                .device_id = 4,
                .max_speed_hz = 100000,
                .mode = NO_OS_SPI_MODE_2,
                .chip_select = 0,
                .platform_ops = &max_spi_ops,
                .extra = &max_spi_extra,
        },
        .op_mode = AD7490_MODE_NORMAL,
        .vdd = AD7490_VDD_5V,
};
int ret, i;
int16_t val;

ret = ad7490_init(&ad7490, &ad7490_ip);
if (ret)
        goto error;

AD7490 no-OS IIO Support

The AD7490 IIO driver comes on top of AD7490 driver and offers support for interfacing IIO clients through IIO lib.

IIO AD7490 Device Configuration

Device Attributes

AD7490 IIO device has a total of 2 device attributes:

range - The range can be selected as REFIN (2.5V) or 2x REFIN (5V)
polarity - The polarity can be selected as UNIPOLAR or BIPOLAR.
sampling_frequency - The sampling frequency for AD7490 (1MSPS).

Device Channels

AD7490 IIO device has 16 input channels : 16 voltage channels.

The voltage channels are :

Channel 0: Voltage
Channel 1: Voltage
Channel 2: Voltage
Channel 3: Voltage
Channel 4: Voltage
Channel 5: Voltage
Channel 6: Voltage
Channel 7: Voltage
Channel 8: Voltage
Channel 9: Voltage
Channel 10: Voltage
Channel 11: Voltage
Channel 12: Voltage
Channel 13: Voltage
Channel 14: Voltage
Channel 15: Voltage

Each voltage channel has 2 attributes:

raw - the raw voltage value read from the device.
scale - is the scale that has to be applied to the raw value in order to obtain the converted real value in Volts. It depends on the selected range and has a specific formula.

In order to obtain the value in the V units, raw has to be scaled by scale:

converted_voltage [V] = raw * scale
converted_voltage [V] = raw * (range/4096)

Device buffers

The AD7490 IIO devices driver supports the usage of a data buffer for reading purposes.

AD7490 IIO Driver Initialization Example

#define DATA_BUFFER_SIZE 400
uint8_t iio_data_buffer[DATA_BUFFER_SIZE * 16 * sizeof(int16_t)];
struct ad7490_iio_desc *ad7490_iio_desc;
struct ad7490_iio_init_param ad7490_iio_ip;
struct iio_app_desc *app;
struct iio_data_buffer voltage_buff = {
        .buff = (void *)iio_data_buffer,
        .size = DATA_BUFFER_SIZE * 16 * sizeof(int16_t)
};
struct iio_app_init_param app_init_param = {0};
int ret;

ad7490_iio_ip.ad7490_init = &ad7490_ip;
ad7490_iio_ip.dout_state = AD7490_DOUT_TRISTATE;
ad7490_iio_ip.range = AD7490_RANGE_REFIN;
ad7490_iio_ip.coding = AD7490_CODING_BINARY;
ret = ad7490_iio_init(&ad7490_iio_desc, &ad7490_iio_ip);
if (ret)
        return ret;

struct iio_app_device iio_devices[] = {
        {
                .name = "ad7490",
                .dev = ad7490_iio_desc,
                .dev_descriptor = ad7490_iio_desc->iio_dev,
                .read_buff = &voltage_buff,
        },
};

app_init_param.devices = iio_devices;
app_init_param.nb_devices = NO_OS_ARRAY_SIZE(iio_devices);
app_init_param.uart_init_params = uart_ip;

ret = iio_app_init(&app, app_init_param);
if (ret)
        return ret;

return iio_app_run(app);