Speed up and harden USB/Bluetooth remote control

[GrzegorzZajac000]

Faster, more robust USB/Bluetooth remote control (screenshots + protocol hardening)

Summary

This PR improves the speed and reliability of the serial/BLE remote-control path
(Remote.cpp and the BLE modules) without changing any existing behaviour on the
wire. The headline items are a much faster screenshot capture, a new compact
binary screenshot command, and several fixes that stop the cooperative main loop
from stalling or watchdog-rebooting during remote transfers.

All changes compile on both PSRAM profiles (esp32s3-ospi, esp32s3-qspi) and
both hardware variants (standard SI4732 Mini/Pocket and LILYGO_SI473X), with no
new #if guards.

Screenshot capture

• Faster C (hex BMP) capture — byte-for-byte identical output.
  The pixel loop previously issued 320 × 170 = 54,400 readPixel() + printf("%04x", …)
  calls plus 170 println() calls per capture. It now reads the sprite framebuffer
  directly via spr.getPointer(), formats each row with a nibble lookup table, and
  emits one stream->write() per row — ~170 stream operations instead of ~54,570.
  The emitted bytes are unchanged (the stored framebuffer word equals
  htons(readPixel(x,y)), and the nibble LUT reproduces %04x exactly), so every
  existing consumer keeps working.

• New binary screenshot command c. Emits the same image as a raw little-endian
  RGB565 BMP, preceded by a short ASCII frame BMP:<size>\r\n. It is about half the
  bytes on the wire of the hex C command (~108 KB vs ~218 KB) and decodes to a
  byte-identical image (equivalent to xxd-decoding the C output). C is left
  completely unchanged; c is purely additive.

• Larger USB CDC TX ring buffer. Serial.setTxBufferSize(4096) is set before
  Serial.begin() so bulk output (screenshots) drains more smoothly with fewer
  producer stalls. A comment also documents that the 115200 argument is only a CDC
  line-coding label under USBMode=hwcdc and does not limit throughput.

Remote-protocol robustness (USB + BLE)

• No more watchdog reboot on a mid-command BLE disconnect. remoteReadChar() and
  the multi-byte parsers (remoteReadInteger / remoteReadString / expectNewline)
  previously busy-spun forever if the link dropped while a command (F…, #…, ^…)
  was only partially received. They now wait with a bounded deadline and yield with
  delay(1), so a disconnect degrades gracefully instead of starving the loop into a
  task-watchdog reset. Interactive multi-byte commands typed a key at a time still
  work, because the parsers still block while data is genuinely arriving.
  (The peek() comparisons were also made independent of char signedness.)

• $ memory dump no longer freezes the UI over BLE. The dump now streams one
  populated slot per loop tick instead of pushing all slots in a single blocking
  burst (which froze encoder/display/RDS for ~1.7 s on BLE). The wire format is
  unchanged.

• Error replies no longer echo leftover input. remoteShowError() drains the
  remaining input silently instead of echoing each leftover byte back before the
  Error: line.

• Minor: remoteTickTime() reads millis() once per tick instead of twice.

Bluetooth LE

• HID scan duty cycle reduced 100% → 25% (interval 400 ms / window 100 ms instead
  of 100 ms / 100 ms). This lowers the RF the 2.4 GHz radio radiates next to the
  SI4732 antenna while scanning, at the cost of slightly longer (imperceptible)
  one-time pairing discovery.

• BLE central TX power set to 0 dBm (ESP_PWR_LVL_N0), matching the peripheral,
  instead of the stack default (~+9 dBm).

• Removed blocking delay(500) calls (and a blank-screen flash) on the HID scan and
  connect paths. The status message is drawn once and persists until the next
  redraw, so the loop stays responsive during pairing.

Docs & changelog

• docs/source/remote.md: documents the new c command and the stable C output
  format, and recommends socat -T5 (idle timeout) plus a note that screenshots over
  BLE are slow.
• Changelog fragments added under changelog/.

Compatibility / risk

• C output is byte-for-byte identical to before; c is a new, previously-unused
  command letter, so no existing consumer is affected.
• No protocol change for any existing command; the $ dump format is unchanged.
• Builds verified for esp32s3-ospi, esp32s3-qspi, and the LILYGO_SI473X and
  HALF_STEP compile-time options.

Testing

• Compiled all four build combinations above with arduino-cli (pinned core/libraries
  from sketch.yaml).
• Verified off-device that the c binary output is byte-identical to xxd-decoding
  the C output and that the resulting BMP header is well-formed.
• Docs build passes with --fail-on-warning --nitpicky.

[Copilot]

Pull request overview

This PR improves the performance and robustness of the USB/BLE remote-control pathway by optimizing screenshot streaming, adding a new compact binary screenshot command, and preventing main-loop stalls during partial/failed remote transfers (including over BLE).

Changes:

• Speed up existing C screenshot capture (hex BMP) by streaming rows from the framebuffer with far fewer stream operations, while keeping output stable.
• Add new c command for binary BMP screenshots with a simple ASCII framing line to reduce on-wire size.
• Harden remote parsing and BLE behaviors to avoid watchdog resets and reduce UI stalls (chunked $ dump, bounded waits, reduced HID scan duty cycle, TX power adjustment, removed blocking delays).

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
docs/source/remote.md	Documents new c command and clarifies screenshot formats and usage examples.
changelog/+screenshot-speed.changed.md	Changelog entry for faster C screenshot path and larger USB TX buffer.
changelog/+screenshot-binary.added.md	Changelog entry for new binary screenshot command c.
changelog/+remote-protocol-robustness.fixed.md	Changelog entry for remote protocol hardening and $ dump responsiveness fixes.
changelog/+ble-scan-rf.changed.md	Changelog entry for BLE HID scan duty cycle, TX power, and responsiveness improvements.
ats-mini/Remote.h	Adds state and API for chunked $ memory dump tick.
ats-mini/Remote.cpp	Implements faster C, new binary c, bounded read/peek waits, chunked $ dump, and less chatty error draining.
ats-mini/BleMode.cpp	Integrates remote tick + chunked memory dump tick into BLE ad-hoc mode; removes blocking delay/flash in HID connect UI.
ats-mini/BleHidCentral.h	Adjusts BLE scan interval/window to reduce duty cycle; documents rationale.
ats-mini/BleHidCentral.cpp	Removes blocking delay/blank-screen flash during HID scan start.
ats-mini/BleCentral.cpp	Sets BLE central TX power to 0 dBm to match peripheral.
ats-mini/ats-mini.ino	Enlarges USB CDC TX buffer before Serial.begin() and documents why.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.