From c7fdd534bcdee71a448276088a5099d9d2abfcca Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 23 Apr 2026 04:44:05 -0500
Subject: [PATCH] [core] Raise WDT_FEED_INTERVAL_MS to 2000ms on BK72xx
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BK72xx silicon requires a ~200us busy-wait (sctrl_dpll_delay200us) between
two watchdog register key writes on every reload, making each
arch_feed_wdt() call ~300us on BK7231T/N/BK7238. This is hardware errata
in the BDK's wdt_ctrl (beken378/driver/wdt/wdt.c:WCMD_RELOAD_PERIOD) and
cannot be worked around at the SDK level.

LibreTiny initialises the BK72xx HW watchdog at 10000ms, but ESPHome's
generic WDT_FEED_INTERVAL_MS of 300ms was sized for ESP8266's 1.6s soft
watchdog. That left BK72xx over-servicing the watchdog ~33x per timeout
window, paying ~60ms/min of main-loop overhead to no benefit.

Raise the interval to 2000ms on BK72xx only, which keeps a 5x safety
margin on the 10s HW WDT — matching the ESP8266 ratio that originally
motivated the 300ms value — while cutting feed frequency ~6x.

Measured on a NiceMCU XH-WB3S (BK7238) while testing
libretiny-eu/libretiny#360:

  Before (300ms interval):
    wdt_slow_path: hits=195 (5.9% of iters, avg=315.97us/hit)
    main_loop_before_breakdown: sched=73.2ms, wdt=61.6ms, residual=0.0ms

Other platforms retain the existing 300ms value.
---
 esphome/core/application.h | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/esphome/core/application.h b/esphome/core/application.h
index 8280b3bd4b..9dc397f526 100644
--- a/esphome/core/application.h
+++ b/esphome/core/application.h
@@ -219,11 +219,22 @@ class Application {
   /// loops and scheduler items still feed after every op, so any op exceeding
   /// this threshold triggers a real feed naturally.
   /// Safety margins vs. platform watchdog timeouts:
-  ///   - ESP32 task WDT default (5 s): ~16x
-  ///   - ESP8266 soft WDT (~1.6 s):    ~5x  <-- floor case; any future change
-  ///                                             must keep comfortable margin here
-  ///   - ESP8266 HW WDT (~6 s):        ~20x
+  ///   - ESP32 task WDT default (5 s):  ~16x
+  ///   - ESP8266 soft WDT (~1.6 s):     ~5x  <-- floor case; any future change
+  ///                                              must keep comfortable margin here
+  ///   - ESP8266 HW WDT (~6 s):         ~20x
+  ///   - BK72xx HW WDT (10 s):          ~5x  <-- platform override below
+#ifdef USE_BK72XX
+  /// BK72xx silicon requires a ~200 µs busy-wait between two watchdog register
+  /// key writes on every reload (sctrl_dpll_delay200us() in BDK wdt.c), making
+  /// each arch_feed_wdt() ~300 µs. LibreTiny initialises the HW WDT at 10 s,
+  /// so 2000 ms keeps a 5x safety margin — matching the ESP8266 ratio that
+  /// motivated the generic 300 ms value — while cutting feed frequency ~6x
+  /// and recovering ~50 ms/min of main-loop overhead on typical configs.
+  static constexpr uint32_t WDT_FEED_INTERVAL_MS = 2000;
+#else
   static constexpr uint32_t WDT_FEED_INTERVAL_MS = 300;
+#endif
 
   /// Feed the task watchdog. Cold entry — callers without a millis()
   /// timestamp in hand. Out of line to keep call sites tiny.