Honor board_build.f_cpu on the native compile line

The routed override (published configs pin 160000000L for
timing-sensitive integrations) reaches -DF_CPU via a small _pio_option
reader; the default stays the audited 80 MHz all 45 boards ship.

esphome/build_gen/arduino8266.py

@@ -298,6 +298,19 @@ def _resolve_build_config(defines: dict[str, str]) -> _BuildConfig:
     )
 
 
+def _pio_option(key: str, default: str) -> str:
+    """A platformio_options value the native build honors (str-normalized).
+
+    Routed into ``CORE.platformio_options`` by core/config.py under the
+    arduino toolchain; a repeated option accumulates as a list, where the
+    last value wins like a later platformio.ini line.
+    """
+    value = CORE.platformio_options.get(key)
+    if isinstance(value, list):
+        value = value[-1] if value else None
+    return default if value is None else str(value)
+
+
 def _defines_flags(
     config: _BuildConfig, flash_mode: str, board: str, board_defines: tuple[str, ...]
 ) -> list[str]:
@@ -310,10 +323,11 @@ def _defines_flags(
     return [
         f"-D{d}"
         for d in (
-            # Upstream reads this from the board manifest (build.f_cpu); all
-            # 45 supported boards ship 80000000L, so the value is hardcoded
-            # here rather than drift (same rationale as _MMU_DEFAULT)
-            "F_CPU=80000000L",
+            # Upstream reads this from the board manifest (build.f_cpu),
+            # where all 45 supported boards ship 80000000L, overridable via
+            # board_build.f_cpu; published configs pin 160000000L for
+            # timing-sensitive integrations, so the override is honored
+            f"F_CPU={_pio_option('board_build.f_cpu', '80000000L')}",
             "__ets__",
             "ICACHE_FLASH",
             "_GNU_SOURCE",

tests/unit_tests/build_gen/test_arduino8266.py

@@ -887,3 +887,20 @@ def test_generate_ld_scripts_gcc_change_invalidates_stamp(tmp_path: Path) -> Non
     with patch.object(arduino8266.subprocess, "run", return_value=result) as mock_run:
         _run_generate_ld_scripts(paths)
     mock_run.assert_called_once()
+
+
+def test_defines_flags_honors_f_cpu_override() -> None:
+    """board_build.f_cpu (a published-config overclock knob) reaches the
+    compile line; the default stays 80 MHz."""
+    _set_flags()
+    config = _resolve_build_config(_flag_defines(set(), []))
+    board_build = ESP8266_BOARD_BUILD["nodemcuv2"]
+    defines = _defines_flags(config, "dout", "nodemcuv2", board_build["defines"])
+    assert "-DF_CPU=80000000L" in defines
+    CORE.platformio_options = {"board_build.f_cpu": "160000000L"}
+    defines = _defines_flags(config, "dout", "nodemcuv2", board_build["defines"])
+    assert "-DF_CPU=160000000L" in defines
+    # A repeated option accumulates as a list; the last value wins
+    CORE.platformio_options = {"board_build.f_cpu": ["80000000L", "160000000L"]}
+    defines = _defines_flags(config, "dout", "nodemcuv2", board_build["defines"])
+    assert "-DF_CPU=160000000L" in defines