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Reduce RTC memory footprint from 32 to 20 bytes

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Pack backtrace count into the magic word and reduce max backtrace
entries from 6 to 4, saving 3 RTC blocks (12 bytes).
This commit is contained in:
J. Nick Koston
2026-04-05 11:52:02 -10:00
parent 50073a24b5
commit 8dc30bc54d
1 changed files with 20 additions and 16 deletions
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esphome/components/esp8266/crash_handler.cpp
+20 -16
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@@ -36,23 +36,28 @@ static inline uint32_t IRAM_ATTR recover_code_addr(uint32_t val) { return (val &
// RTC user memory layout for crash backtrace data.
// User-accessible RTC memory: blocks 64-191 (each block = 4 bytes).
// We use blocks 184-191 (last 8 blocks) to minimize conflicts with other users.
static constexpr uint8_t RTC_CRASH_BASE = 184;
static constexpr uint32_t CRASH_MAGIC_SENTINEL = 0xDEAD0000;
static constexpr uint32_t CRASH_DATA_VERSION = 1;
static constexpr uint32_t CRASH_MAGIC_V1 = CRASH_MAGIC_SENTINEL | CRASH_DATA_VERSION;
static constexpr size_t MAX_BACKTRACE = 6;
// We use blocks 187-191 (last 5 blocks, 20 bytes) to minimize conflicts.
static constexpr uint8_t RTC_CRASH_BASE = 187;
static constexpr size_t MAX_BACKTRACE = 4;
// Struct layout matches 8 RTC blocks (32 bytes):
// [0] = magic (0xDEAD0001)
// [1..6] = up to 6 code addresses from stack scanning
// [7] = backtrace count (lower 8 bits)
// Magic word packs sentinel, version, and count into one uint32_t:
// bits[31:16] = 0xDEAD (sentinel)
// bits[15:8] = version (1)
// bits[7:0] = backtrace count
static constexpr uint32_t CRASH_SENTINEL = 0xDEAD0000;
static constexpr uint32_t CRASH_VERSION = 0x00000100; // version 1 in bits[15:8]
static constexpr uint32_t CRASH_SENTINEL_MASK = 0xFFFF0000;
static constexpr uint32_t CRASH_VERSION_MASK = 0x0000FF00;
static constexpr uint32_t CRASH_COUNT_MASK = 0x000000FF;
// Struct layout: 5 RTC blocks (20 bytes):
// [0] = magic (sentinel | version | count)
// [1..4] = up to 4 code addresses from stack scanning
struct RtcCrashData {
uint32_t magic;
uint32_t backtrace[MAX_BACKTRACE];
uint32_t backtrace_count; // Only lower 8 bits used; uint32_t for RTC alignment
};
static_assert(sizeof(RtcCrashData) == 32, "RtcCrashData must fit in 8 RTC blocks");
static_assert(sizeof(RtcCrashData) == 20, "RtcCrashData must fit in 5 RTC blocks");
namespace esphome::esp8266 {
@@ -144,9 +149,9 @@ static uint8_t read_rtc_backtrace(uint32_t *backtrace, size_t max_entries) {
if (!system_rtc_mem_read(RTC_CRASH_BASE, &rtc_data, sizeof(rtc_data)))
return 0;
uint32_t magic = rtc_data.magic;
if ((magic & 0xFFFF0000) != CRASH_MAGIC_SENTINEL || (magic & 0xFFFF) != CRASH_DATA_VERSION)
if ((magic & CRASH_SENTINEL_MASK) != CRASH_SENTINEL || (magic & CRASH_VERSION_MASK) != CRASH_VERSION)
return 0;
uint8_t count = rtc_data.backtrace_count;
uint8_t count = magic & CRASH_COUNT_MASK;
if (count > max_entries)
count = max_entries;
for (uint8_t i = 0; i < count; i++) {
@@ -228,8 +233,7 @@ extern "C" void IRAM_ATTR custom_crash_callback(struct rst_info * /*rst_info*/,
}
}
data.backtrace_count = count;
data.magic = CRASH_MAGIC_V1;
data.magic = CRASH_SENTINEL | CRASH_VERSION | count;
system_rtc_mem_write(RTC_CRASH_BASE, &data, sizeof(data));
}