Two changes against the whole-screen colour flash.
1. Real fix for the flash testers see BEFORE the boot splash. The panel was
switched on and only then was the framebuffer cleared, so the DSI streamed a
freshly-allocated (garbage) PSRAM buffer to the screen until the clear caught
up. Blank it with a memset + cache flush while the panel is still dark. That
also removes 39 back-to-back draw_bitmap transfers into a buffer the panel is
scanning out.
2. Diagnostic, P4 only: LVGL bands 24 -> 64 lines. This panel is DSI video mode
with a SINGLE framebuffer, so every band is copied into the buffer being
actively scanned. At 24 lines a full-screen repaint is ~26 back-to-back
transfers into that live buffer. The reported triggers (message arrives,
opening a chat with unread, adding/deleting a contact) all rebuild the whole
screen; panning the map repaints only its own region and never flashes, which
is the shape this predicts. Wider bands cut the same repaint to ~10
transfers. Sized so the 2x upscale scratch still fits internal SRAM, so burst
count is the only variable that moves.
Supersedes the write-path theory: the flash still occurs with contacts, history
and prefs all on SD, and the pre-splash case involves no write at all.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
