The panel driver now splits writing a frame into its SPI buffer
(epd_write_frame(), which also computes a CRC32 as it streams) from
actually triggering the physical refresh (epd_turn_on_display()).
frame_client.c compares the new CRC against the last one that was
actually refreshed (persisted in NVS) and skips the refresh entirely
when they match -- e.g. a reboot redisplaying the same photo before the
server's refresh interval elapsed no longer causes a visible flash for
no visual change.
Also reorders the per-wake fetch cycle: the image fetch (15s timeout)
now goes before the config check (3s timeout), instead of after. The
config check's tighter timeout was intermittently tripping on
connection-setup latency that's common on the first request after
waking from a long deep sleep (e.g. stale ARP); putting the more
tolerant request first absorbs that latency, and the config check then
rides the connection it already warmed up.
Ports Waveshare's official EPD_7in3e.c register/refresh sequence (the
panel has no public datasheet, so their reference driver is the source of
truth) to an ESP-IDF component using spi_master + gpio instead of the
bcm2835/RPi hardware abstraction the reference targets.
Unlike the reference driver, which toggles CS around every single byte,
this holds CS low for each logical command/data phase and DMAs pixel data
in 4KB chunks -- sending ~192,000 individual one-byte SPI transactions
would make a full refresh impractically slow.
Exposes a streaming API (epd_display_stream, pulling chunks from a
caller-supplied read_fn) so the eventual HTTP fetch path can feed the panel
without holding a full ~192KB frame in RAM, plus an in-memory convenience
wrapper (epd_display_buffer) for cases like the upcoming QR code screen
where buffering the whole frame is fine.
Wired into wifi_provisioning_start() as an init + white-clear for now, to
prove the driver builds/links/runs at the right point in the boot sequence
ahead of the actual QR code content.
tfaour