Heltec T114 automatic screen detection

The canonical T114 firmware now includes the optional ST7789 screen driver and checks for the stock screen at boot. Screenless boards use the same firmware. Legacy without_display build names remain compatibility aliases; automatic release selection uses the canonical targets.

Hardware basis

Heltec's stock panel specification identifies the controller as ST7789V2 and describes SDA as an SPI input/output pin. The existing T114 wiring supports register reads over this shared data line; a separate MISO wire is unnecessary.

The Sitronix controller specification documents the read-ID command and serial turnaround on pages 58–64 and 167, and reset recovery on pages 48–49. Its ID bytes are programmable, so detection does not require a single guessed factory ID.

Expected behavior

The backlight stays off during a bounded boot probe, before framebuffer allocation and display SPI startup.
Consistent ID responses with both data-line pull directions distinguish a responding panel from floating, stuck, or unstable inputs.
An absent panel or failed display initialization leaves display power off. Later drawing and wake requests cannot start an absent panel.
Companion button events remain safe without a display. Notification acknowledgement, buzzer toggling and early-boot CLI rescue remain available; visual navigation is skipped when there is no display.
A detected panel retains normal rendering, sleep, wake, and display settings.
Detection is specific to the T114 automatic-display recipe. Other boards using the shared ST7789 driver retain their existing behavior.
The RAM gate budgets a responding screen even when a particular board boots headless. The T114 display needs two 4,080-byte buffers and one temporary 480-byte RGB565 row: 8,640 bytes of peak heap allocation, in addition to the normal allocator and transient margin. The same model follows the shared driver's T190 and M9 panel sizes and its single-buffer configuration.
Picker consolidation requires evidence from the exact published application. Historical releases retain their original screen behavior and update IDs.

Validation

Check	Result
Native probe, GPIO, headless and wake regressions	PASS, 4 methods with ASan/UBSan; late-turnaround, reset-delay and floating-line negative controls
Resolved recipe and compatibility-alias checks	PASS, 5 methods; actual PlatformIO configuration also confirms all 5 legacy aliases match their canonical targets
Companion headless buttons and related navigation, reader, pairing, startup and deadline suites	PASS, 55 methods, including native headless fault regression and 4 input/reader configurations
Picker and release-selection regressions	PASS, 78 Python methods and 3 Node suites; old assets, scoped previews, newest-role defaults and unavailable legacy choices covered
Display allocation accounting and firmware RAM gates	PASS, 46 methods, including production allocation tracking across 3 panel sizes and buffer configurations
T114 firmware and package checks	PASS, all 8 published profiles; UF2/DFU application bytes, hashes, version, hardware/OTA identity, flash limits, display capability and RAM admission checked
Hosted documentation links	PASS, 7 methods
Physical T114 with and without a screen	Not performed

The T114 1.18.0.1 preview1 packages firmware source 794f5f7b8c508b708ee8fc7db7bff066aa3d1a0a. Its seven display-capable profiles contain the verified automatic-detection marker; the eighth is the headless KISS utility. The published qualification report records each profile's flash range, retained update identity and RAM allowance. Repeater Full has the smallest RAM margin at 10,200 bytes after the display allocation and normal transient margin. KISS has no embedded EndF version or update identity; its package provenance, UF2/DFU application equality, flash bounds, hashes and RAM gate are checked.

The release-bound picker check offers those eight profiles under the single canonical T114 hardware choice, with seven automatic-display profiles and one headless KISS profile. It preserves all 111 other hardware profiles from the current main release and retains historical T114 files as exact downloads.

Native tests simulate controller replies and GPIO state; they do not establish physical detection reliability. Before calling the hardware qualified, test cold USB and battery boots with a stock screen and with no screen, then verify screen sleep/wake, Bluetooth/USB connections, and normal radio receive/transmit.