SDADC Example

Source code path: example/rt_device/adc/sdadc

Overview

  • Under the RT-Thread operating system, the SDADC peripheral is virtualized as an rt_device. It is accessed through the standard RT ADC framework (rt_device_find + rt_adc_enable + rt_adc_read) via the "sdadc" device to perform voltage sampling.

  • This example demonstrates the complete chain of multi-channel scanning + timer trigger + interrupt notification (event-driven): GPTIM3 periodically triggers a scan round → the hardware refreshes each channel’s result into its corresponding output register → the conversion-complete interrupt fires → the driver callback rx_indicate wakes up the application → the application reads the latest voltage of each channel one by one.

Supported Platforms

The example can run on the following development board.

  • sf32lb58 HDK

Note: The SDADC IP is only available on SF32LB55X and SF32LB58X chips. This example was debugged on the 58 series.

Sampling Modes Supported by the SDADC Driver

The SDADC driver supports two orthogonal dimensions, which are combined through Kconfig:

Dimension

Option

Description

Channel count

BSP_SDADC_SUPPORT_MULTI_CH_SAMPLING

Off: single channel; On: multi-channel scanning (configure once, sample multiple channels separately)

Trigger source

BSP_SDADC_USE_TIMER_TRIGGER

Off: software trigger (actively starts a conversion on read); On: GPTIM3 timer trigger, with conversion-complete interrupt enabled

All four combinations are available: single channel + software trigger, single channel + timer trigger, multi-channel + software trigger, multi-channel + timer trigger. This example uses multi-channel + timer trigger + interrupt notification by default.

Hardware Connection

Mapping between SDADC channels and pins (driver channel numbers 1~4):

Chip

CH1

CH2

CH3

CH4

SF32LB55X

PB_23

PB_24

PB_25

PB_26

SF32LB58X

PB_40

PB_41

PB_42

PB_43

Connect the target SDADC pin to an external voltage source (0 ~ reference voltage). GND must share a common ground with the development board. A channel with no signal connected will read floating noise, which is normal.

Usage

Build and Flash

  • This example uses the SDADC RT driver. Make sure rtconfig.h contains the following macros:

#define BSP_USING_SDADC 1
#define RT_USING_ADC 1

Only when these macros are present will the sifli_sdadc_init function register the "sdadc" device through rt_hw_adc_register, allowing subsequent rt_device_find and rt_adc_read calls to succeed.

  • The proj.conf of this example already enables the required configuration:

CONFIG_BSP_USING_SDADC=y
CONFIG_BSP_SDADC_USE_TIMER_TRIGGER=y       # Timer trigger + conversion-complete interrupt
CONFIG_BSP_SDADC_TIMER_PERIOD_MS=1000      # Timer period (ms)
CONFIG_BSP_SDADC_SUPPORT_MULTI_CH_SAMPLING=y   # Multi-channel scanning

  • For manual configuration, use menuconfig (replace your_board with the board name you actually use):

sdk.py menuconfig --board=your_board

Select the SDADC, multi-channel sampling, timer trigger and other options as shown, then save and exit. alt text

  • Switch to the example project directory and run scons to build (using ec-lb587 as an example):

scons --board=ec-lb587_hcpu -j8

  • Run build_ec-lb587_hcpu\uart_download.bat and follow the prompts to select the serial port for download.

Example Output:

Each time a conversion-complete interrupt notification is received (approximately equal to the timer period), a set of 4-channel voltage values is printed (in 0.1mV units; ch1: 6580 (658.0 mV) means 658.0mV):

======== SDADC Multi-Channel (IRQ-driven) Example ========
I/sdadc: SDADC ch1 enabled
I/sdadc: SDADC ch2 enabled
I/sdadc: SDADC ch3 enabled
I/sdadc: SDADC ch4 enabled
I/sdadc: SDADC multi-channel + timer trigger + interrupt, 4 channels
msh />
I/sdadc: ch1: 7025 (702.5 mV)
I/sdadc: ch2: 4761 (476.1 mV)
I/sdadc: ch3: 6618 (661.8 mV)
I/sdadc: ch4: 6391 (639.1 mV)

If SDADC conversion-complete notification timeout is printed continuously, it means no interrupt notification was received. Check whether the timer trigger and the SDADC interrupt are working properly.

Example Flow

  1. Configure pinmux for each channel to be sampled (HAL_PIN_Set + HAL_PIN_Select to switch to the SDADC analog function)

  2. rt_device_find("sdadc") to find the SDADC device

  3. For each channel, rt_adc_enable(dev, channel) to enable the corresponding sampling slot.

  4. Initialize the semaphore and register the conversion-complete callback with rt_device_set_rx_indicate

  5. In the main loop, rt_sem_take waits to be woken by the interrupt notification, then rt_adc_read reads the voltage of each channel

Switching to Other Sampling Modes

  • Single channel: In proj.conf, remove CONFIG_BSP_SDADC_SUPPORT_MULTI_CH_SAMPLING=y, and change g_sdadc_channels in main.c to a single channel (e.g. {3}).

  • Software trigger: Remove CONFIG_BSP_SDADC_USE_TIMER_TRIGGER=y. In this case there is no timer or conversion-complete interrupt; each rt_adc_read actively starts a conversion (blocking until complete). The application side should revert to the rt_thread_mdelay + rt_adc_read polling approach and no longer wait for rx_indicate.

  • Timer without interrupt notification: Keep the timer trigger, but do not call rt_device_set_rx_indicate. The main loop can simply poll with rt_thread_mdelay + rt_adc_read.

Troubleshooting

  • find sdadc failed — BSP_USING_SDADC is not enabled, the SDADC driver is not compiled, and the "sdadc" device is not registered.

  • rt_adc_enable chN failed — the channel number is out of range (valid 1~4), or SDADC hardware initialization failed.

  • SDADC conversion-complete notification timeout — no interrupt notification received: confirm that BSP_SDADC_USE_TIMER_TRIGGER is enabled (the driver enables both the timer trigger and the conversion-complete interrupt), and check whether GPTIM3 is running properly.

  • A channel always reads 0 or abnormal values —

    1. Check whether the channel pin has a signal connected and shares a common ground with the board;

    2. Check whether the HAL_PIN_Select function selection value for the pad is correct (this example uniformly uses 10; if a channel does not match, refer to the pin configuration table to confirm);

    3. In multi-channel mode, confirm that the channel has been rt_adc_enabled (a slot that has not been enabled will not be scanned).

    4. Check whether the chip’s SDADC has been factory-calibrated. Check whether the Get SDADC configure fail, use default calibration log appears in the boot log.

Revision History

Version

Date

Release Notes

0.0.1

07/2026

Initial version