[esp8266] Replace millis() with fast accumulator, wrap Arduino callers (#15662)

esphome/components/esp8266/__init__.py

@@ -314,6 +314,11 @@ async def to_code(config):
         for symbol in ("vprintf", "printf", "fprintf"):
             cg.add_build_flag(f"-Wl,--wrap={symbol}")
 
+    # Wrap Arduino's millis() so all callers (including Arduino libraries and ISR
+    # handlers) use our fast accumulator instead of the expensive 4x 64-bit multiply
+    # implementation in the Arduino ESP8266 core.
+    cg.add_build_flag("-Wl,--wrap=millis")
+
     cg.add_platformio_option("board_build.flash_mode", config[CONF_BOARD_FLASH_MODE])
 
     ver: cv.Version = CORE.data[KEY_CORE][KEY_FRAMEWORK_VERSION]

esphome/components/esp8266/core.cpp

@@ -16,9 +16,75 @@ extern "C" {
 namespace esphome {
 
 void HOT yield() { ::yield(); }
-uint32_t IRAM_ATTR HOT millis() { return ::millis(); }
-uint64_t millis_64() { return Millis64Impl::compute(::millis()); }
-void HOT delay(uint32_t ms) { ::delay(ms); }
+// Fast accumulator replacement for Arduino's millis() (~3.3 μs via 4× 64-bit
+// multiplies on the LX106). Tracks a running ms counter from 32-bit
+// system_get_time() deltas using pure 32-bit ops. Installed as __wrap_millis
+// (via -Wl,--wrap=millis) so Arduino libs and IRAM_ATTR ISR handlers (e.g.
+// Wiegand, ZyAura) also get the fast version. xt_rsil(15) guards the static
+// state against ISR re-entry; the critical section is bounded (≤10 while-loop
+// iterations, ~100 ns on the common path, or a constant-time /1000 ~2.5 μs on
+// the rare path — well under WiFi's ~10 μs ISR latency budget). NMIs (level
+// >15) are not masked, but the ESP8266 SDK's NMI handlers don't call millis().
+//
+// system_get_time() wraps every ~71.6 min; unsigned (now_us - last_us) handles
+// one wrap. The main loop calls millis() at 60+ Hz, so delta stays tiny — a
+// >71 min block would trip the watchdog long before it could matter here.
+static constexpr uint32_t MILLIS_RARE_PATH_THRESHOLD_US = 10000;
+static constexpr uint32_t US_PER_MS = 1000;
+
+uint32_t IRAM_ATTR HOT millis() {
+  // Struct packs the three statics so the compiler loads one base address
+  // instead of three separate literal pool entries (saves ~8 bytes IRAM).
+  static struct {
+    uint32_t cache;
+    uint32_t remainder;
+    uint32_t last_us;
+  } state = {0, 0, 0};
+  uint32_t ps = xt_rsil(15);
+  uint32_t now_us = system_get_time();
+  uint32_t delta = now_us - state.last_us;
+  state.last_us = now_us;
+  state.remainder += delta;
+  if (state.remainder >= MILLIS_RARE_PATH_THRESHOLD_US) {
+    // Rare path: large gap (WiFi scan, boot, long block). Constant-time
+    // conversion keeps the critical section bounded.
+    uint32_t ms = state.remainder / US_PER_MS;
+    state.cache += ms;
+    // Reuse ms instead of `remainder %= US_PER_MS` — `%` would compile to a
+    // second __umodsi3 call on the LX106 (no hardware divide).
+    state.remainder -= ms * US_PER_MS;
+  } else {
+    // Common path: small gap. At most ~10 iterations since remainder was
+    // < threshold (10 ms) on entry and delta adds at most one more threshold
+    // before exiting this branch.
+    while (state.remainder >= US_PER_MS) {
+      state.cache++;
+      state.remainder -= US_PER_MS;
+    }
+  }
+  uint32_t result = state.cache;
+  xt_wsr_ps(ps);
+  return result;
+}
+uint64_t millis_64() { return Millis64Impl::compute(millis()); }
+// Poll-based delay that avoids ::delay() — Arduino's __delay has an intra-object
+// call to the original millis() that --wrap can't intercept, so calling ::delay()
+// would keep the slow Arduino millis body alive in IRAM. optimistic_yield still
+// enters esp_schedule()/esp_suspend_within_cont() via yield(), so SDK tasks and
+// WiFi run correctly. Theoretically less power-efficient than Arduino's
+// os_timer-based delay() for long waits, but nearly all ESPHome delays are short
+// (sensor/I²C/SPI settling in the 1–100 ms range) where the difference is
+// negligible.
+void HOT delay(uint32_t ms) {
+  if (ms == 0) {
+    optimistic_yield(1000);
+    return;
+  }
+  uint32_t start = millis();
+  while (millis() - start < ms) {
+    optimistic_yield(1000);
+  }
+}
 uint32_t IRAM_ATTR HOT micros() { return ::micros(); }
 void IRAM_ATTR HOT delayMicroseconds(uint32_t us) { delay_microseconds_safe(us); }
 void arch_restart() {
@@ -78,4 +144,12 @@ extern "C" void resetPins() {  // NOLINT
 
 }  // namespace esphome
 
+// Linker wrap: redirect all ::millis() calls (Arduino libs, ISRs) to our accumulator.
+// Requires -Wl,--wrap=millis in build flags (added by __init__.py).
+// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp,readability-identifier-naming)
+extern "C" uint32_t IRAM_ATTR __wrap_millis() { return esphome::millis(); }
+// Note: Arduino's init() registers a 60-second overflow timer for micros64().
+// We leave it running — wrapping init() as a no-op would break micros64()'s
+// overflow tracking, and the timer's cost is negligible (~3 μs per 60 s).
+
 #endif  // USE_ESP8266