This description uses Linux kernel > 3.7.
LRADC is a 12 bits 16 channels Analog to Digital Converter integrated into the i.MX28 processor.
Only channels 0-6 may be used to generic conversions and channels 2, 3, 4, 5 are used for the touchscreen on APF28Dev.
- Channel 0 is available on J10 pin 38 of APF28Dev
- Channel 1 is available on J10 pin 36 of APF28Dev
- Channel 6 is available on J10 pin 35 of APF28Dev
Driver is by default included if you choose an APF28 as target.
Otherwise, you can select it that way:
[ ] $ make linux-menuconfig
Device Drivers ---> <M> Staging drivers ---> IIO staging drivers Analog to digital converters <M> Freescale i.MX28 LRADC
Then compile the distribution :
[ ] $ make linux && make
To use the LRADC, first load mxs-lradc module:
# modprobe mxs-lradc
Read channels value
# cd /sys/bus/iio/devices/iio:device0 # ls buffer in_voltage11_raw in_voltage2_raw name dev in_voltage12_raw in_voltage3_raw power in_temp8_raw in_voltage13_raw in_voltage4_raw scan_elements in_temp9_raw in_voltage14_raw in_voltage5_raw subsystem in_voltage0_raw in_voltage15_raw in_voltage6_raw trigger in_voltage10_raw in_voltage1_raw in_voltage7_raw uevent
To read ADC value just «cat» the corresponding input file:
# cat in_voltage0_raw for channel 0 4095
All values are not converted (ie. directly show the register content). To have the mV value, you must do: value_mV = in_voltageX_raw * 1850/4095