58. Decode ADC Result Using Union Bitfields

#include <stdio.h>
#include <stdint.h>

typedef union {
    struct {
        uint16_t adc_value : 12;
        uint16_t channel   : 4;
    };
    uint16_t adc_reg;
} ADC_Result;

int main() {
    uint16_t reg;
    scanf("%hx", &reg); // Read hexadecimal input

    ADC_Result result;
    result.adc_reg = reg;

    printf("Channel: %u\n", result.channel);
    printf("ADC Value: %u", result.adc_value);
    return 0;
}

What is this about?

This mimics a real ADC result register layout where raw analog values and their source channel are packed into one word. 

Why it’s important in firmware?

• Real hardware often overlays multiple fields into one register
• Efficient parsing without using bit masking everywhere
• Cleaner access via result.channel and result.adc_value
   

Solution Logic

• Bitfield order matches hardware layout
• 12 LSBs used for ADC result
• Top 4 bits for channel
• Union lets us access both the full value and individual fields