ADC Acquisition Application

This chapter describes the GK7206 ADC (analog-to-digital converter) acquisition application example — sample_lsadc. The application demonstrates reading ADC channel data through the /dev/lsadc device node, and supports two working modes: single-step scan and continuous scan.

The application source code is located in the SDK directory sample/lsadc/. It is a simple hardware peripheral access example that shows how to interact with a hardware driver through the Linux character device interface.

1 Application Overview

1.1 Features

  • Dual scan modes: supports single-step scan and continuous scan working modes
  • Multi-channel selection: supports selecting different ADC input channels
  • Interactive operation: select the mode and channel via the command line
  • Real-time data display: prints the acquired ADC values in real time
  • Low memory footprint: minimal memory usage with no complex dependencies

1.2 Technical Specifications

ParameterValue
Device node/dev/lsadc
Scan modessingle-step scan, continuous scan
Sampling interval1 second (adjustable)
Acquisition count20 (default)
Memory footprintMinimal
Kernel modulerequires xm_lsadc.ko

1.3 Directory Structure

sample/lsadc/
├── Makefile              # Build script
└── sample_lsadc.c       # Main program

2 Build and Deployment

2.1 Prerequisites

Before building this application, make sure the following preparations have been completed:

  1. SDK environment is set up: follow SDK Compilation to set up the cross-compilation toolchain and SDK configuration
  2. Kernel module is loaded: the xm_lsadc.ko module must be loaded

2.2 Build the Application

# Enter the sample directory
cd <SDK_PATH>/sample

# lsadc is not in the top-level objects; build it separately
make -C lsadc clean && make -C lsadc

Tips

The lsadc sample is not in the objects list of the top-level Makefile and must be built separately.

2.3 Deploy to the Board

# Transfer to the development board via SCP
scp sample/lsadc/sample_lsadc root@<board IP>:/tmp/

# Or download via TFTP
tftp -g -r sample_lsadc <board IP>

Info

Since this application is very small, it can run directly from /tmp.

2.4 Run the Application

# Add execute permission
chmod +x /tmp/sample_lsadc

# Load the kernel module (required on first run)
insmod /opt/ko/xm_lsadc.ko

# Run the application (interactive)
./sample_lsadc

2.5 Expected Output

Startup screen

=============== LSADC TEST ===============
0:single step scan mode
1:continuous scan mode
please select the mode:

Single-step scan mode (select mode 0)

After selecting the channel:

please select the channel:
0
get value:1234,chn[0]
get value:1235,chn[0]
get value:1233,chn[0]
get value:1236,chn[0]
get value:1234,chn[0]
get value:1237,chn[0]
get value:1232,chn[0]
get value:1238,chn[0]
get value:1235,chn[0]
get value:1239,chn[0]
get value:1233,chn[0]
get value:1236,chn[0]
get value:1234,chn[0]
get value:1237,chn[0]
get value:1232,chn[0]
get value:1238,chn[0]
get value:1235,chn[0]
get value:1239,chn[0]
get value:1233,chn[0]
get value:1236,chn[0]

Expected behavior:

  • Prints get value:<ADC value>,chn[<channel>] 20 times in a loop
  • Prints once per second (usleep(1000*1000))
  • ADC value range: 0~4095 (12-bit ADC)
  • The ADC value varies with the input voltage
  • Exits automatically after 20 readings

Continuous scan mode (select mode 1)

After selecting the channel:

please select the channel:
0
get value:1234,chn[0]
get value:1235,chn[0]
get value:1233,chn[0]
get value:1236,chn[0]
get value:1234,chn[0]
get value:1237,chn[0]
get value:1232,chn[0]
get value:1238,chn[0]
get value:1235,chn[0]
get value:1239,chn[0]
get value:1233,chn[0]
get value:1236,chn[0]
get value:1234,chn[0]
get value:1237,chn[0]
get value:1232,chn[0]
get value:1238,chn[0]
get value:1235,chn[0]
get value:1239,chn[0]
get value:1233,chn[0]
get value:1236,chn[0]

Expected behavior:

  • Prints get value:<ADC value>,chn[<channel>] 20 times in a loop
  • Prints once per second
  • The ADC value varies with the input voltage
  • Exits automatically after 20 readings

How to exit

  • Automatic exit: exits automatically after 20 acquisitions
  • Manual exit: press Ctrl+C to force exit

Error cases

fail to open file:/dev/lsadc

Cause: the xm_lsadc.ko kernel module is not loaded Solution: insmod /opt/ko/xm_lsadc.ko

adc model select error.

Cause: invalid mode argument Solution: make sure to enter 0 or 1

2.5 Interactive Operation

Single-step scan mode

please select the mode: 0
please select the channel: 0
get value:1234,chn[0]
get value:1235,chn[0]
...

Continuous scan mode

please select the mode: 1
please select the channel: 0
get value:1234,chn[0]
get value:1235,chn[0]
...

3 Internal Execution Logic in Detail

3.1 Application Architecture

This application uses a simple interactive architecture:

int main(void)
{
    int mode, chn;

    // Show the menu
    printf("=============== LSADC TEST ===============\n");
    printf("0:single step scan mode\n");
    printf("1:continuous scan mode\n");
    printf("please select the mode:\n");

    // Read user input
    scanf("%d", &mode);

    // Select the scan mode based on the mode value
    switch(mode) {
        case 0:
            printf("please select the channel:\n");
            scanf("%d", &chn);
            sample_lsadc_single_step_scan_mode(mode, chn);
            break;
        case 1:
            printf("please select the channel:\n");
            scanf("%d", &chn);
            sample_lsadc_continuous_scan_mode(mode, chn);
            break;
        default:
            printf("invalid mode\n");
            break;
    }

    return 0;
}

3.2 Single-Step Scan Mode

Each acquisition in single-step scan mode requires the full start → read → stop sequence:

xmedia_s32 sample_lsadc_single_step_scan_mode(lsadc_scan_mode mode, xmedia_s32 chn)
{
    int i, value;
    int fd = open(DEV_FILE, O_RDWR);  // Open /dev/lsadc

    if (fd < 0) {
        fprintf(stderr, "fail to open file:%s\n", DEV_FILE);
        return -1;
    }

    // Select the scan mode
    if(ioctl(fd, LSADC_IOC_MODEL_SEL, &mode) < 0) {
        fprintf(stderr, "adc model select error.\n");
        goto exit;
    }

    // Enable the channel
    if(ioctl(fd, LSADC_IOC_CHN_ENABLE, &chn) < 0) {
        fprintf(stderr, "enable chn %d error.\n", chn);
        goto exit;
    }

    // Acquire 20 samples in a loop
    for(i = 0; i < 20; i++) {
        // Start the ADC
        if(ioctl(fd, LSADC_IOC_START) < 0) {
            fprintf(stderr, "start lsadc error.\n");
            goto exit;
        }

        // Read the channel value
        value = ioctl(fd, LSADC_IOC_GET_CHNVAL, &chn);
        printf("get value:%d,chn[%d]\n", value, chn);
        usleep(1000 * 1000);  // Wait 1 second

        // Stop the ADC
        if(ioctl(fd, LSADC_IOC_STOP) < 0) {
            fprintf(stderr, "stop lsadc error.\n");
        }
    }

exit:
    // Clean up
    if(ioctl(fd, LSADC_IOC_STOP) < 0) {
        fprintf(stderr, "stop lsadc error.\n");
    }
    if(ioctl(fd, LSADC_IOC_CHN_DISABLE, &chn) < 0) {
        fprintf(stderr, "disable chn %d error.\n", chn);
    }
    close(fd);
    return 0;
}

3.3 Continuous Scan Mode

Continuous scan mode starts the ADC only once, then keeps reading data:

xmedia_s32 sample_lsadc_continuous_scan_mode(lsadc_scan_mode mode, xmedia_s32 chn)
{
    int i, value;
    int fd = open(DEV_FILE, O_RDWR);

    if (fd < 0) {
        fprintf(stderr, "fail to open file:%s\n", DEV_FILE);
        return -1;
    }

    // Select the scan mode
    if(ioctl(fd, LSADC_IOC_MODEL_SEL, &mode) < 0) {
        fprintf(stderr, "adc model select error.\n");
        goto exit;
    }

    // Enable the channel
    if(ioctl(fd, LSADC_IOC_CHN_ENABLE, &chn) < 0) {
        fprintf(stderr, "enable chn %d error.\n", chn);
        goto exit;
    }

    // Start the ADC (started only once)
    if(ioctl(fd, LSADC_IOC_START) < 0) {
        fprintf(stderr, "start lsadc error.\n");
        goto exit;
    }

    // Read data in a loop
    for(i = 0; i < 20; i++) {
        value = ioctl(fd, LSADC_IOC_GET_CHNVAL, &chn);
        printf("get value:%d,chn[%d]\n", value, chn);
        usleep(1000 * 1000);  // Wait 1 second
    }

exit:
    // Clean up
    if(ioctl(fd, LSADC_IOC_STOP) < 0) {
        fprintf(stderr, "stop lsadc error.\n");
    }
    if(ioctl(fd, LSADC_IOC_CHN_DISABLE, &chn) < 0) {
        fprintf(stderr, "disable chn %d error.\n", chn);
    }
    close(fd);
    return 0;
}

3.4 IOCTL Commands

The application uses the following IOCTL commands to interact with the driver:

CommandFunctionArgument
LSADC_IOC_MODEL_SELSelect scan mode0=single-step, 1=continuous
LSADC_IOC_CHN_ENABLEEnable channelChannel number
LSADC_IOC_CHN_DISABLEDisable channelChannel number
LSADC_IOC_STARTStart the ADCNone
LSADC_IOC_STOPStop the ADCNone
LSADC_IOC_GET_CHNVALGet channel valueChannel number

3.5 Meaning of the ADC Value

The value returned by the ADC is an integer, typically in the range 0~4095 (12-bit ADC). The value is proportional to the input voltage:

voltage = (ADC value / 4095) × reference voltage

For example, with a 3.3 V reference voltage and an ADC value of 2048, the input voltage is approximately:

voltage = (2048 / 4095) × 3.3V ≈ 1.65V

4 Key Programming Points

4.1 Device Node Operations

The standard operating pattern for a Linux character device:

// Open the device
int fd = open("/dev/lsadc", O_RDWR);

// IOCTL control
ioctl(fd, LSADC_IOC_MODEL_SEL, &mode);

// Close the device
close(fd);

4.2 Error Handling

Check the return value of every IOCTL call:

if(ioctl(fd, LSADC_IOC_START) < 0) {
    fprintf(stderr, "start lsadc error.\n");
    goto exit;  // Jump to the cleanup code
}

4.3 Resource Cleanup

Use goto for unified resource cleanup:

exit:
    // Disable the channel
    if(ioctl(fd, LSADC_IOC_CHN_DISABLE, &chn) < 0) {
        fprintf(stderr, "disable chn %d error.\n", chn);
    }
    // Close the device
    close(fd);
    return 0;
}

5 Troubleshooting

ProblemPossible causeSolution
fail to open file:/dev/lsadcDevice node does not existCheck whether xm_lsadc.ko is loaded
adc model select errorInvalid mode argumentCheck that mode is 0 or 1
enable chn X errorInvalid channel numberCheck that the channel number is in a valid range
ADC value always 0Input not connected or voltage too lowCheck the hardware connection
ADC value always 4095Input voltage too high or above the referenceCheck the input voltage range

6 References