MIPI CSI / DSI Overview: Interview Drills

PROMPT
You see lane error rate, frame drop count, blanking budget on MIPI CSI / DSI Overview. Walk through root cause and fix.

STRONG ANSWER
1. Names the layer and transaction identity.
2. Explains MIPI moves camera/display payloads through lane-based high-speed bursts with strict timing and packet framing.
3. Requests lane status trace, frame timing report, packet decode log.
4. Proposes one reduced sequence and one system regression.

WEAK ANSWER
Jumps to widening the interface, increasing FIFO depth, or blaming firmware without evidence.

MIPI D-PHY LANES

clock lane ‾‾‾‾‾‾‾‾‾‾ (DDR clock)
data lane0 == HS burst == LP idle == HS burst ==
data lane1 == HS burst == LP idle == HS burst ==

HS (high-speed) for pixels, LP (low-power) for control.
Frame = packets with line start/end; blanking gives PHY time to switch.

ROOT-CAUSE TREE — MIPI CSI / DSI Overview

lane error rate, frame drop count, blanking budget looks wrong
        |
   reproducible?
     /        \
   no          yes
   |            |
 flaky env   same first transaction every time?
 / seed         /            \
              yes             no
               |               |
        protocol rule     timing/reset/PVT
        or config bug     or load-dependent

HIGH-SPEED STACK

app -> MAC/framing -> PCS/encoding -> SerDes/PHY -> channel

CRC errors often mean PCS/PHY/channel, not TCP.

BER vs EQ SETTING

BER
1e-3 |*
1e-6 |  *
1e-9 |     **** usable window
1e-12|          *
     +-----------------> EQ tap