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[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.
This commit is contained in:
J. Nick Koston
2026-04-23 04:44:05 -05:00
parent 43a371caab
commit c7fdd534bc
1 changed files with 15 additions and 4 deletions
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esphome/core/application.h
+15 -4
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@@ -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.