ADC over spidev

The code

Embedded Linux C. It compiles. There are 3 real bugs in it: the kind that pass a bench test and fail in the field.

int adc_read(int fd, int ch, uint16_t *out)
{
    uint8_t tx[3] = { 0x01, (uint8_t)((8 + ch) << 4), 0x00 };
    uint8_t rx[3];
    struct spi_ioc_transfer t;
    t.tx_buf = (unsigned long)tx;
    t.rx_buf = (unsigned long)rx;
    t.len = 3;
    t.speed_hz = 1000000;
    ioctl(fd, SPI_IOC_MESSAGE(1), &t);
    *out = (uint16_t)(((rx[1] & 0x03) << 8) | rx[2]);
    return 0;
}

What an interviewer expects

• Point to each line you'd stop in a code review.
• Say what actually breaks: the failure mode, not just the rule it violates.
• Fix it, then defend the fix when asked the follow-up.

The bugs, reference fixes and the follow-up question are in the practice app, after you've tried it.

Companies that test this

Matched on the skills each company's embedded roles emphasise.

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