Serial GPS reader on Linux

The code

Embedded Linux C. It compiles. There are 4 real bugs in it: the kind that pass a bench test and fail in the field.

int gps_open(void)
{
    int fd = open("/dev/ttyS2", O_RDWR);
    struct termios t;
    tcgetattr(fd, &t);
    cfsetispeed(&t, B9600);
    cfsetospeed(&t, B9600);
    tcsetattr(fd, TCSANOW, &t);
    return fd;
}

int gps_read_sentence(int fd, char *out, size_t cap)
{
    ssize_t n = read(fd, out, cap);
    if (n <= 0) return -1;
    out[n] = '\0';
    return (int)n;
}

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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