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Qualcomm's SPMI PMIC voltage ADC
SPMI PMIC voltage ADC (VADC) provides interface to clients to read
voltage. The VADC is a 15-bit sigma-delta ADC.
VADC node:
- compatible:
Usage: required
Value type: <string>
Definition: Should contain "qcom,spmi-vadc".
- reg:
Usage: required
Value type: <prop-encoded-array>
Definition: VADC base address and length in the SPMI PMIC register map.
- #address-cells:
Usage: required
Value type: <u32>
Definition: Must be one. Child node 'reg' property should define ADC
channel number.
- #size-cells:
Usage: required
Value type: <u32>
Definition: Must be zero.
- #io-channel-cells:
Usage: required
Value type: <u32>
Definition: Must be one. For details about IIO bindings see:
Documentation/devicetree/bindings/iio/iio-bindings.txt
- interrupts:
Usage: optional
Value type: <prop-encoded-array>
Definition: End of conversion interrupt.
Channel node properties:
- reg:
Usage: required
Value type: <u32>
Definition: ADC channel number.
See include/dt-bindings/iio/qcom,spmi-vadc.h
- qcom,decimation:
Usage: optional
Value type: <u32>
Definition: This parameter is used to decrease ADC sampling rate.
Quicker measurements can be made by reducing decimation ratio.
Valid values are 512, 1024, 2048, 4096.
If property is not found, default value of 512 will be used.
- qcom,pre-scaling:
Usage: optional
Value type: <u32 array>
Definition: Used for scaling the channel input signal before the signal is
fed to VADC. The configuration for this node is to know the
pre-determined ratio and use it for post scaling. Select one from
the following options.
<1 1>, <1 3>, <1 4>, <1 6>, <1 20>, <1 8>, <10 81>, <1 10>
If property is not found default value depending on chip will be used.
- qcom,ratiometric:
Usage: optional
Value type: <empty>
Definition: Channel calibration type. If this property is specified
VADC will use the VDD reference (1.8V) and GND for channel
calibration. If property is not found, channel will be
calibrated with 0.625V and 1.25V reference channels, also
known as absolute calibration.
- qcom,hw-settle-time:
Usage: optional
Value type: <u32>
Definition: Time between AMUX getting configured and the ADC starting
conversion. Delay = 100us * (value) for value < 11, and
2ms * (value - 10) otherwise.
Valid values are: 0, 100, 200, 300, 400, 500, 600, 700, 800,
900 us and 1, 2, 4, 6, 8, 10 ms
If property is not found, channel will use 0us.
- qcom,avg-samples:
Usage: optional
Value type: <u32>
Definition: Number of samples to be used for measurement.
Averaging provides the option to obtain a single measurement
from the ADC that is an average of multiple samples. The value
selected is 2^(value).
Valid values are: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512
If property is not found, 1 sample will be used.
NOTE:
Following channels, also known as reference point channels, are used for
result calibration and their channel configuration nodes should be defined:
VADC_REF_625MV and/or VADC_SPARE1(based on PMIC version) VADC_REF_1250MV,
VADC_GND_REF and VADC_VDD_VADC.
Example:
/* VADC node */
pmic_vadc: vadc@3100 {
compatible = "qcom,spmi-vadc";
reg = <0x3100 0x100>;
interrupts = <0x0 0x31 0x0 IRQ_TYPE_EDGE_RISING>;
#address-cells = <1>;
#size-cells = <0>;
#io-channel-cells = <1>;
io-channel-ranges;
/* Channel node */
usb_id_nopull {
reg = <VADC_LR_MUX10_USB_ID>;
qcom,decimation = <512>;
qcom,ratiometric;
qcom,hw-settle-time = <200>;
qcom,avg-samples = <1>;
qcom,pre-scaling = <1 3>;
};
};
/* IIO client node */
usb {
io-channels = <&pmic_vadc VADC_LR_MUX10_USB_ID>;
io-channel-names = "vadc";
};
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