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Experiment 02: Modetest Mastery & Practical Troubleshooting

1. Core Command Syntax

  • Set Mode (-s): modetest -M rockchip -s <Connector_ID>@<CRTC_ID>:<Mode>
  • Write Property (-w): modetest -M rockchip -w <Object_ID>:<Prop>:<Value>
  • Set Plane (-P): modetest -M rockchip -P <Plane_ID>@<CRTC_ID>:<w>x<h>+<x>+<y>

2. Troubleshooting: "Object ID Not Found"

While attempting to modify the DPMS property, an Object not found error occurred.

  • Root Cause: Mistaking the Encoder ID for the Connector ID.
  • Solution: Properties like DPMS are attached to the Connector. Always use the ID from the leftmost column in the modetest -c list.

3. Engineering Insights

modetest acts as both a register configurator and a "Graphic Producer." Its built-in color bar pattern is the fastest way to verify the integrity of the display link (from Framebuffer to physical screen) without a full GUI stack.