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[esp8266][rp2040] Eliminate heap fallback in preference save/load

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Replace SmallBufferWithHeapFallback with a fixed stack buffer sized
to the physical storage limit. No single preference can exceed the
storage it resides in, so heap allocation is never needed.

ESP8266: buffer sized to max(flash_storage, rtc_normal_region) —
128 words (512B) with restore_from_flash, 96 words (384B) without.
RP2040: buffer sized to flash storage (512B).

Eliminates new[]/delete[] codegen from save()/load() virtual methods.
This commit is contained in:
J. Nick Koston
2026-02-11 07:27:24 -06:00
parent 38bba3f5a2
commit fe5088c6e1
2 changed files with 27 additions and 25 deletions
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29
esphome/components/esp8266/preferences.cpp
View File

@@ -33,6 +33,10 @@ static constexpr uint32_t MAX_PREFERENCE_WORDS = 255;
#define ESP_RTC_USER_MEM ((uint32_t *) ESP_RTC_USER_MEM_START)
// Flash storage size depends on esp8266 -> restore_from_flash YAML option (default: false).
// When enabled (USE_ESP8266_PREFERENCES_FLASH), all preferences default to flash and need
// 128 words (512 bytes). When disabled, only explicit flash prefs use this storage so
// 64 words (256 bytes) suffices since most preferences go to RTC memory instead.
#ifdef USE_ESP8266_PREFERENCES_FLASH
static constexpr uint32_t ESP8266_FLASH_STORAGE_SIZE = 128;
#else
@@ -127,9 +131,11 @@ static bool load_from_rtc(size_t offset, uint32_t *data, size_t len) {
return true;
}
// Stack buffer size - 16 words total: up to 15 words of preference data + 1 word CRC (60 bytes of preference data)
// This handles virtually all real-world preferences without heap allocation
static constexpr size_t PREF_BUFFER_WORDS = 16;
// Maximum buffer for any single preference - bounded by storage sizes.
// Flash prefs: bounded by ESP8266_FLASH_STORAGE_SIZE (128 or 64 words).
// RTC prefs: bounded by RTC_NORMAL_REGION_WORDS (96) - a single pref can't span both RTC regions.
static constexpr size_t PREF_MAX_BUFFER_WORDS =
ESP8266_FLASH_STORAGE_SIZE > RTC_NORMAL_REGION_WORDS ? ESP8266_FLASH_STORAGE_SIZE : RTC_NORMAL_REGION_WORDS;
class ESP8266PreferenceBackend : public ESPPreferenceBackend {
public:
@@ -141,15 +147,13 @@ class ESP8266PreferenceBackend : public ESPPreferenceBackend {
bool save(const uint8_t *data, size_t len) override {
if (bytes_to_words(len) != this->length_words)
return false;
const size_t buffer_size = static_cast<size_t>(this->length_words) + 1;
SmallBufferWithHeapFallback<PREF_BUFFER_WORDS, uint32_t> buffer_alloc(buffer_size);
uint32_t *buffer = buffer_alloc.get();
if (buffer_size > PREF_MAX_BUFFER_WORDS)
return false;
uint32_t buffer[PREF_MAX_BUFFER_WORDS];
memset(buffer, 0, buffer_size * sizeof(uint32_t));
memcpy(buffer, data, len);
buffer[this->length_words] = calculate_crc(buffer, buffer + this->length_words, this->type);
return this->in_flash ? save_to_flash(this->offset, buffer, buffer_size)
: save_to_rtc(this->offset, buffer, buffer_size);
}
@@ -157,19 +161,16 @@ class ESP8266PreferenceBackend : public ESPPreferenceBackend {
bool load(uint8_t *data, size_t len) override {
if (bytes_to_words(len) != this->length_words)
return false;
const size_t buffer_size = static_cast<size_t>(this->length_words) + 1;
SmallBufferWithHeapFallback<PREF_BUFFER_WORDS, uint32_t> buffer_alloc(buffer_size);
uint32_t *buffer = buffer_alloc.get();
if (buffer_size > PREF_MAX_BUFFER_WORDS)
return false;
uint32_t buffer[PREF_MAX_BUFFER_WORDS];
bool ret = this->in_flash ? load_from_flash(this->offset, buffer, buffer_size)
: load_from_rtc(this->offset, buffer, buffer_size);
if (!ret)
return false;
if (buffer[this->length_words] != calculate_crc(buffer, buffer + this->length_words, this->type))
return false;
memcpy(data, buffer, len);
return true;
}

23
esphome/components/rp2040/preferences.cpp
View File

@@ -25,8 +25,8 @@ static uint8_t
s_flash_storage[RP2040_FLASH_STORAGE_SIZE]; // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
static bool s_flash_dirty = false; // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
// Stack buffer size for preferences - covers virtually all real-world preferences without heap allocation
static constexpr size_t PREF_BUFFER_SIZE = 64;
// No preference can exceed the total flash storage, so stack buffer covers all cases.
static constexpr size_t PREF_MAX_BUFFER_SIZE = RP2040_FLASH_STORAGE_SIZE;
extern "C" uint8_t _EEPROM_start;
@@ -46,14 +46,14 @@ class RP2040PreferenceBackend : public ESPPreferenceBackend {
bool save(const uint8_t *data, size_t len) override {
const size_t buffer_size = len + 1;
SmallBufferWithHeapFallback<PREF_BUFFER_SIZE> buffer_alloc(buffer_size);
uint8_t *buffer = buffer_alloc.get();
if (buffer_size > PREF_MAX_BUFFER_SIZE)
return false;
uint8_t buffer[PREF_MAX_BUFFER_SIZE];
memcpy(buffer, data, len);
buffer[len] = calculate_crc(buffer, buffer + len, type);
buffer[len] = calculate_crc(buffer, buffer + len, this->type);
for (size_t i = 0; i < buffer_size; i++) {
uint32_t j = offset + i;
uint32_t j = this->offset + i;
if (j >= RP2040_FLASH_STORAGE_SIZE)
return false;
uint8_t v = buffer[i];
@@ -66,17 +66,18 @@ class RP2040PreferenceBackend : public ESPPreferenceBackend {
}
bool load(uint8_t *data, size_t len) override {
const size_t buffer_size = len + 1;
SmallBufferWithHeapFallback<PREF_BUFFER_SIZE> buffer_alloc(buffer_size);
uint8_t *buffer = buffer_alloc.get();
if (buffer_size > PREF_MAX_BUFFER_SIZE)
return false;
uint8_t buffer[PREF_MAX_BUFFER_SIZE];
for (size_t i = 0; i < buffer_size; i++) {
uint32_t j = offset + i;
uint32_t j = this->offset + i;
if (j >= RP2040_FLASH_STORAGE_SIZE)
return false;
buffer[i] = s_flash_storage[j];
}
uint8_t crc = calculate_crc(buffer, buffer + len, type);
uint8_t crc = calculate_crc(buffer, buffer + len, this->type);
if (buffer[len] != crc) {
return false;
}