LTDC double buffering

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.

static uint16_t fb[2][320 * 240];
static int draw_idx = 0;

/* Called by the app after drawing into fb[draw_idx] */
void frame_done(void)
{
    LTDC_Layer1->CFBAR = (uint32_t)fb[draw_idx];
    LTDC->SRCR = LTDC_SRCR_IMR;
    draw_idx ^= 1;
    memset(fb[draw_idx], 0, sizeof fb[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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