diff --git a/esphome/components/libretiny/__init__.py b/esphome/components/libretiny/__init__.py index c63d6d7faa..93b66888da 100644 --- a/esphome/components/libretiny/__init__.py +++ b/esphome/components/libretiny/__init__.py @@ -261,6 +261,10 @@ async def component_to_code(config): cg.add_build_flag(f"-DUSE_LIBRETINY_VARIANT_{config[CONF_FAMILY]}") cg.add_define("ESPHOME_BOARD", config[CONF_BOARD]) cg.add_define("ESPHOME_VARIANT", FAMILY_FRIENDLY[config[CONF_FAMILY]]) + # LibreTiny uses MULTI_NO_ATOMICS because platforms like BK7231N (ARM968E-S) lack + # exclusive load/store (no LDREX/STREX). std::atomic RMW operations require libatomic, + # which is not linked to save flash (4-8KB). Even if linked, libatomic would use locks + # (ATOMIC_INT_LOCK_FREE=1), so explicit FreeRTOS mutexes are simpler and equivalent. cg.add_define(ThreadModel.MULTI_NO_ATOMICS) # force using arduino framework diff --git a/esphome/const.py b/esphome/const.py index b4cd3cfd1c..2b6b60d395 100644 --- a/esphome/const.py +++ b/esphome/const.py @@ -36,7 +36,30 @@ class Framework(StrEnum): class ThreadModel(StrEnum): - """Threading model identifiers for ESPHome scheduler.""" + """Threading model identifiers for ESPHome scheduler. + + ESPHome currently uses three threading models based on platform capabilities: + + SINGLE: + - Single-threaded platforms (ESP8266, RP2040) + - No RTOS task switching + - No concurrent access to scheduler data structures + - No atomics or locks required + - Minimal overhead + + MULTI_NO_ATOMICS: + - Multi-threaded platforms without hardware atomic RMW support (e.g. LibreTiny BK7231N) + - Uses FreeRTOS or another RTOS with multiple tasks + - CPU lacks exclusive load/store instructions (ARM968E-S has no LDREX/STREX) + - std::atomic cannot provide lock-free RMW; libatomic is avoided to save flash (4–8 KB) + - Scheduler uses explicit FreeRTOS mutexes for synchronization + + MULTI_ATOMICS: + - Multi-threaded platforms with hardware atomic RMW support (ESP32, Cortex-M, Host) + - CPU provides native atomic instructions (ESP32 S32C1I, ARM LDREX/STREX) + - std::atomic is used for lock-free synchronization + - Reduced contention and better performance + """ SINGLE = "ESPHOME_THREAD_SINGLE" MULTI_NO_ATOMICS = "ESPHOME_THREAD_MULTI_NO_ATOMICS"