docs: IMX335 at full resolution -- the encoder binds, and line WDR needs the sensor held to it

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Adds a subsection to the IMX335 part of docs/high-framerate-modes.md. The existing tables stream 1920x1080, where the encoder is not the bottleneck. At the full 2592x1944 frame it is.

• Encoder ceiling (gk7205v300, stock 30 fps mode, 60 s per reading): asked for 26, H.264 and H.265 both encode 21 fps and VI loses 5 frames a second. Asked for 20, both encode 20 and nothing is lost. That is about 107 Mpixel/s, the same rate as the hi3516ev300's 54 fps at 1080p and 121 fps at 720p in the HMAX table.

• 5M line WDR: VI shares its buffer pool with the encoder, so each 2592x1944 keyframe costs a VI frame while the sensor runs at 22, even with the stream decimated to 20 or 15. With the sensor at 20, nothing is lost. A linear 30 fps sensor decimated to 20 loses nothing.

• Ruled out, each changing nothing:

  • the ISP back end (VIPROC) clocked at 360 MHz via PERI_CRG63[3] rather than 257 MHz; its time per frame fell from 23.2 to 16.6 ms;
  • a bigger VB pool;
  • JPEG off.

  VI, VPSS and VEDU are already on their top documented clocks.

Documentation only.

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PR Summary by Qodo

Document IMX335 full-resolution encoder limits and WDR frame loss

📝 Documentation 🕐 Less than 10 minutes

AI Description

• Document the gk7205v300’s full-resolution encoder ceiling and a loss-free 20 fps setting.
• Explain why 5M line WDR also needs the sensor held to 20 fps.
• Record clock, buffer-pool, and JPEG tests that did not prevent frame loss.

Diagram

graph TD
  S["IMX335 sensor"] --> V["VI capture"] --> B["Shared VB pool"] --> E["Video encoder"] --> O["Encoded stream"]
  E -. "keyframe stall" .-> B
  B -. "22 fps WDR" .-> L["VI frame loss"]

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High-Level Assessment

Keep the measurements alongside the existing IMX335 mode tables. A separate document would split closely related frame-rate guidance without adding value.

Files changed (1) +41 / -0

Documentation (1) +41 / -0

high-framerate-modes.mdDocument full-resolution IMX335 encoding and line-WDR limits +41/-0

Document full-resolution IMX335 encoding and line-WDR limits

• Adds measured H.264 and H.265 rates at 2592×1944, identifying a roughly 21 fps encoder ceiling and a loss-free 20 fps setting. Explains why the 5M line-WDR sensor must also run at 20 fps, contrasts linear mode, and records unsuccessful clock, VB-pool, and JPEG mitigations.

docs/high-framerate-modes.md