Serial command parser

The code

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

#define CMD_MAX 32
static char    cmd[CMD_MAX];
static uint8_t pos;

void on_rx_char(char c)
{
    if (c == '\r') {
        cmd[pos] = '\0';
        handle_command(cmd);
        pos = 0;
    } else {
        cmd[pos++] = c;
    }
}

void handle_command(char *s)
{
    if (strncmp(s, "SET ", 4) == 0) {
        int v = atoi(s + 4);
        set_brightness(v);
    }
}

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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