Add Bed zones

[ellensp]

Description

This PR adds a BED_ZONES feature that divides a heated print bed into independently controlled heating zones. Each zone has its own heater output pin and thermistor input pin. Zones are selected individually or in groups via a bitmask.

The primary motivation is large-format printers and specialty beds where different physical areas need independent temperature control — e.g. heating only the front half of the bed for a small print, or tuning PID independently per zone.

What is implemented

Configuration (Configuration_adv.h)

• #define BED_ZONES — opt-in feature flag, guarded by HAS_HEATED_BED
• BED_ZONES_COUNT — number of zones (1–16, must be an explicit integer literal for preprocessor use)
• BED_ZONE_HEATER_PINS / BED_ZONE_SENSOR_PINS — per-zone pin arrays; zone 0 always maps to HEATER_BED_PIN / TEMP_BED_PIN
• BED_ZONE_MASK_COUNT / BED_ZONE_MASKS — optional numbered bitmask presets (no string names; presets referenced by index only)
• BED_ZONE_PID_VALUES — per-zone default PID coefficients
• SanityCheck.h — static_assert validates pin array lengths match BED_ZONES_COUNT; error if BED_ZONES enabled without HAS_HEATED_BED

Temperature Core (temperature.cpp / temperature.h)

• temp_bed expanded from scalar TempInfo to temp_bed[BED_ZONES_COUNT] array
• Back-compat accessors: degBed() / wholeDegBed() / degTargetBed() return the hottest active zone value (safety-relevant, matches what the status screen shows)
• setTargetBed(celsius, mask) — applies target to all zones selected by bitmask
• isHeatingBed() / isCoolingBed() — zone-mask-aware
• wait_for_bed() — waits until all active-mask zones reach target within TEMP_BED_HYSTERESIS
• Bang-bang and PID control loops iterate all zones independently
• Per-zone ISR PWM output: zone 0 uses WRITE_HEATER_BED / soft_pwm_bed; zones 1+ use extDigitalWrite with soft_pwm_bed_zone[] (required for runtime-variable pins on AVR)
• Per-zone ADC reads: each zone has its own PrepareTemp_BED_ZONEn / MeasureTemp_BED_ZONEn ISR state pair; analog_to_celsius_bed takes an optional zone parameter
• BED_ZONE_SENSOR_TYPES — per-zone thermistor type override (defaults to TEMP_SENSOR_BED); full thermistor table dispatch per zone
• Per-zone thermal runaway — tr_state_machine_bed[BED_ZONES_COUNT] gives each zone an independent THERMAL_PROTECTION_BED state machine; MAXTEMP/MINTEMP checked per zone
• Per-zone heating watchdog — watch_bed_zone[BED_ZONES_COUNT] replaces scalar watch_bed
• Pin initialisation iterates all zone heater pins via pinMode + extDigitalWrite

G-Code

G-Code	Change
M140 / M190	New A<index> (single zone) and K<bitmask> (zone group) parameters; falls back to persistent active mask
M142 (new)	Set/report the persistent active zone mask; K<mask>, A<index>, P<preset>
M105	Reports B0:<t>/<target> B1:… B<n>@:<pwm> for all zones
M303	New A<index> parameter to autotune a specific bed zone; autotune finish message and result line use zone-aware format (M304 A<n> P… I… D…)
M304	New A<index> parameter to set/report PID for a specific zone; M503 reports one echo: M304 A<n> … line per zone

EEPROM (settings.cpp)

• Active zone mask (bed_zone_mask) stored and restored
• Per-zone PID values (bedZonePIDs[BED_ZONES_COUNT]) stored and restored
• EEPROM version bumped to V91

LCD Menus

• menu_temperature.cpp / menu_tune.cpp: single Bed item replaced by per-zone Bed Zone 0 … Bed Zone N-1 loop when HAS_BED_ZONES; all zone temperatures visible and editable from the standard temperature/tune menus (no separate detail screen needed)
• menu_advanced.cpp: per-zone P/I/D edit items and per-zone PID autotune items (PID_EDIT_MENU + PID_AUTOTUNE_MENU)
• language_en.h: added MSG_BED_ZONE_N = _UxGT("Bed Zone ~") (tilde replaced by zone index at render time)
• Status screen B: field: shows hottest active zone (via updated degBed() / degTargetBed())

Controller Fan

• CONTROLLER_FAN_BED_HEATING uses zone-mask-aware isHeatingBed()

Probing / Calibration (probe.cpp, G76_M871.cpp)

• All setTargetBed() calls in probe.cpp and G76_M871.cpp pass no mask and use the zone-aware overload's default mask=0xFFFF — all zones are heated before probing/calibration. Since zone geometry is not stored there is no way to know which zone is under the probe; heating all zones is the only correct behaviour.
• wholeDegBed(), degTargetBed(), and wait_for_bed_heating() are already zone-aware (return/compare against the hottest active zone). No code changes were required in either file.

LCD Preheat (marlinui.cpp)

• apply_preheat() passes bed_zone_mask to setTargetBed() so preheat presets (M145 / LCD preheat menu) only heat the currently active zones.

Build / Feature Guards

• HAS_BED_ZONES macro: true when BED_ZONES enabled and BED_ZONES_COUNT > 1
• features.ini: HAS_BED_ZONES = build_src_filter=+<src/gcode/temp/M142.cpp>
• All new code is additive behind #if HAS_BED_ZONES / #else guards — non-zone builds are unaffected

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Requirements

• A board with multiple independently switchable bed heater outputs and thermistor inputs (e.g. a large-format printer controller)
• HAS_HEATED_BED and PIDTEMPBED recommended (bang-bang also works per-zone)
• For the simulator: SDL2 + MarlinSimUI from the ellensp/MarlinSimUI test-bed-zones branch (fetched automatically via lib_deps)

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Benefits

• Independent temperature control per bed zone — heat only the area being printed on
• Per-zone PID tuning and autotune
• Thermal runaway protection is independent per zone — a failed zone does not mask failures in others
• Fully back-compatible: non-zone builds (BED_ZONES disabled) compile and behave identically to before; all new paths are behind HAS_BED_ZONES guards

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Configurations

Currently tested with:

• mega2560 (AVR ATmega2560) — clean build, no regressions
• simulator_linux_debug (Linux native sim) — builds and runs; M105/M140/M190/M142/M303/M304/M503 verified via terminal

test_config_for_sim.zip

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Related Issues

[FR] Dual zone heated bed support #4112

[ellensp]

Thoughts? G-codes use? Parameter letters? over all?