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Rockchip Developer Guide Linux SARADC

ID: RK-KF-YF-084

Release Version: V 1.0.0

Release Date: 2019-12-23

Security Level: □Top-Secret □Secret □Internal ■Public

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Preface

Overview

SARADC is a 6-channel 10-bit effective digital-to-analog converter, when the input frequency is 13MHz, the conversion speed is 1MSPS

Product Version

ChipsetKernel Version
ALL4.4&4.19

Intended Audience

This document (this guide) is mainly intended for:

Technical support engineers Software development engineers

Revision History

VersionAuthorDateChange Description
V1.0.0Simon.Xue2019-12-23Initial version

Content

[TOC]​

SARADC Driver​

The driver file is in: drivers/iio/adc/rockchip_saradc.c

DTS Configuration​

The reference document for DTS configuration is Documentation/devicetree/bindings/iio/adc/rockchip-saradc.txt, this document mainly introduces the following parameter:

  • interrupts = <GIC_SPI 62 IRQ_TYPE_LEVEL_HIGH 0>;

    Finish conversion and generate interrupt signal.

  • io-channel-cells = <1>;

    Here value must be 1, and the explanation refer to iio-bindings.txt

  • vref-supply = <&vccadc_ref>;

    The reference voltage matched to the SARADC value needs to be set according to the specific hardware environment, the maximum is 1.8V, the corresponding SARADC value is 1024, and the voltage and the ADC value have a linear relationship.

Usage of SARADC​

  1. SARADC depends on the "iio" framework, you need to initialize the structure struct iio_dev, please see indio_dev of the rockchip_saradc_probe function, finally call iio_device_register (indio_dev) to register indio_dev, waiting for the "input" framework to use.

  2. Take "adc-key" as an example, you need to initialize struct input_polled_dev, please see the adc_keys_probe function in drivers/input/keyboard/adc-keys.c for detail, call input_register_polled_device (poll_dev); and register to the" input "framework.

  3. When using getevent test, assuming that adc-key is event0, then getevent -s /dev/input/event0 will have the following calling relationship: adc_keys_poll-> iio_read_channel_processed-> iio_channel_read-> rockchip_saradc_read_raw-> iio_convert_raw_to_processed_unlocked

rockchip_saradc_read_raw is an important function, analyzed one by one:

  1. writel_relaxed(8, info->regs + SARADC_DLY_PU_SOC);

    Set the interval from power up to start sampling to 8 sclk cycles.

  2. writel(SARADC_CTRL_POWER_CTRL | (chan->channel & SARADC_CTRL_CHN_MASK) | SARADC_CTRL_IRQ_ENABLE,info->regs + SARADC_CTRL);

    1. Power up saradc
    2. Set the sampling channel
    3. Enable interrupt and start sampling

  3. wait_for_completion_timeout(&info->completion, SARADC_TIMEOUT)

    Wait for SARADC to complete sampling and generate an interrupt.

  4. *val = info->last_val;

    Store the sampled data into val.

  5. Convert the sampled data to the corresponding voltage value by calling iio_convert_raw_to_processed_unlocked.

Interrupt processing: function rockchip_saradc_isr :

  1. info->last_val = readl_relaxed(info->regs + SARADC_DATA);

    Save the data for usage in step 4 above.

  2. writel_relaxed(0, info->regs + SARADC_CTRL); Clear the interruption, and "power down saradc", shut down the SARADC.

A complete sampling process is rockchip_saradc_read_raw configure SARADC, open SARADC, start sampling, wait for interrupt, clear interrupt in interrupt function and finally close SARADC.

Kernel Configuration​

Symbol: ROCKCHIP_SARADC [=y]
Type  : tristate
Prompt: Rockchip SARADC driver
	Location:
		-> Device Drivers
			-> Industrial I/O support (IIO [=y])
(1)     		-> Analog to digital converters
	Defined at drivers/iio/adc/Kconfig:319
    Depends on: IIO [=y] && (ARCH_ROCKCHIP [=y] || ARM && COMPILE_TEST [=n]) &&
    RESET_CONTROLLER [=y]

Common Interfaces of SARADC​

1.The ADC value can be obtained through the user mode interface, where * indicates the number of ADC channels:

cat /sys/bus/iio/devices/iio\:device0/in_voltage*_raw

For example, channle0:

cat /sys/bus/iio/devices/iio\:device0/in_voltage0_raw

2.Commonly used interfaces of the kernel:

Obtain ADC Value: iio_read_channel_raw()

Obtain Voltage Value: iio_read_channel_processed()