04 - ADC Acquisition Application

This chapter describes the ADC acquisition application example on the Pico-G1 expansion board — adc_display. It demonstrates how to sample analog voltages with the chip's built-in LSADC (12-bit SAR ADC) and display the voltage value in real time on a TFT screen. It is a fundamental example for learning analog signal acquisition.

The application source code lives in the SDK directory source/app/04_adc_display/, providing a complete ADC character-device implementation.

1 Application Overview

1.1 Features

LSADC sampling: demonstrates voltage sampling with the chip's built-in 12-bit ADC
Real-time display: shows the voltage value and raw ADC value on a TFT screen
High-precision display: supports millivolt-level voltage precision
Automatic calibration: supports VREF voltage reference configuration

1.2 Technical Specifications

Parameter	Value
`ADC resolution`	12-bit (0~4095)
`Sampling channel`	CH1 (GPIO1_1)
`VREF voltage`	1.8V (default, configurable)
`Input range`	0~VREF (≤ 3.3V)
`Sampling mode`	CONTINUOUS
`Refresh interval`	100ms (configurable)

1.3 Hardware Connection

Signal	On-board GPIO	Physical pad	Description
AO	GPIO1_1	iocfg_reg21 @ 0x12090004	ADC input channel 1
VCC	1.8V	—	Reference voltage (must be ≤ 3.3V)
GND	GND	—	Ground

2 Build and Deployment

2.1 Building the Application

export PATH=$PATH:<SDK>/tools/linux/toolchains/arm-gcc12.2.0-linux-uclibceabi/bin
cd <SDK>/source/app/04_adc_display
make

2.2 Running the Application

scp adc_display root@<board-IP>:/usr/bin/
ssh root@<board-IP} '/usr/bin/adc_display'

3 Expected Output

3.1 Console output

/mnt # ./adc_display
[adc] pad 0x12090004 -> 0x00001004
[spi] pad 0x100C0028 -> 0x00001004
[spi] pad 0x100C002C -> 0x00001004
[spi] pad 0x100C0030 -> 0x00001000
[spi] pad 0x100C0020 -> 0x00001005
[spi] pad 0x100C001C -> 0x00001005
[spi] opening /dev/spidev2.0 ...
[spi] spidev opened, fd=3
[spi] spidev mode/bits/speed set (MODE3/8b/24MHz)
[spi] chardev request DC  @ /dev/gpiochip4 line 5 ...
[spi] chardev request RES @ /dev/gpiochip4 line 4 ...
[spi] chardev request CS  @ /dev/gpiochip5 line 1 ...
[spi] chardev-verify: DC=0(expect0) RES=1(expect1) CS=1(expect1)  ==> OK(chardev 真驱动了引脚)
[spi] spi_hal_init done
[tft] init: SLPOUT
[tft] init: SLPOUT +120ms ok
[tft] init: config cmds ok
[tft] init: DISPON
[tft] init: DISPON ok
[tft] init: clear-flush start
[tft] flush #1 start
[tft] flush #1 done
[tft] init: clear-flush done
[adc] /dev/lsadc 不存在，自动 insmod xm_lsadc.ko ...
raw=4095  V=3.300
[tft] flush #2 start
[tft] flush #2 done

3.2 TFT screen display

ADC display effect

4 Troubleshooting

Problem	Possible cause	Solution
/dev/lsadc missing	LSADC driver not loaded	The program loads xm_lsadc.ko automatically
Abnormal readings	Wrong VREF configuration	Modify the ADC_VREF_MV parameter
Fluctuating values	Unstable input signal	Add a filtering circuit