ota: detect Tasmota magic numbers when booting (#2370)

- inject dummy data sequence that is expected to hold current version info
- check rtcmem markers and purge settings, since we don't want accidentally reading something as a kv
- sometimes we cannot boot b/c of certain SDK params, purge last 16KiB as well

ref. `SetOption78 1`
https://tasmota.github.io/docs/Commands/#setoptions

The original idea from Esphome:
https://github.com/esphome/esphome/blob/0e59243b83913fc724d0229514a84b6ea14717cc/esphome/core/esphal.cpp#L275-L287
Does not seem to be working atm. Will need to re-check with the esphome builder, c/p did not work and I tried building with gcc-10

Specific things we want to do is to have 'version' byte between 2 'marker' bytes:
https://github.com/arendst/Tasmota/blob/217addc2bb2cf46e7633c93e87954b245cb96556/tasmota/settings.ino#L218-L262       https://github.com/arendst/Tasmota/blob/0dfa38df89c8f2a1e582d53d79243881645be0b8/tasmota/i18n.h#L780-L782

code/espurna/main.cpp

@@ -153,15 +153,11 @@ void setup() {
  info(true);
 
  wifiSetup();
- #if OTA_ARDUINOOTA_SUPPORT
- arduinoOtaSetup();
- #endif
+ otaSetup();
+
  #if TELNET_SUPPORT
  telnetSetup();
  #endif
- #if OTA_CLIENT != OTA_CLIENT_NONE
- otaClientSetup();
- #endif
 
  // -------------------------------------------------------------------------
  // Check if system is stable

code/espurna/ota.cpp

@@ -7,8 +7,12 @@ OTA MODULE COMMON FUNCTIONS
 #include "ota.h"
 #include "system.h"
 #include "terminal.h"
+#include "rtcmem.h"
+#include "utils.h"
 #include "ws.h"
 
+#include <atomic>
+
 void otaPrintError() {
  if (Update.hasError()) {
  #if TERMINAL_SUPPORT
@@ -77,3 +81,45 @@ void otaProgress(size_t bytes, size_t each) {
  last = bytes;
  }
 }
+
+void otaSetup() {
+ // Some magic to allow seamless Tasmota OTA upgrades
+ // - inject dummy data sequence that is expected to hold current version info
+ // - purge settings, since we don't want accidentaly reading something as a kv
+ // - sometimes we cannot boot b/c of certain SDK params, purge last 16KiB
+ {
+ // ref. `SetOption78 1`
+ // - https://tasmota.github.io/docs/Commands/#setoptions (> SetOption78 Version check on Tasmota upgrade)
+ // - https://github.com/esphome/esphome/blob/0e59243b83913fc724d0229514a84b6ea14717cc/esphome/core/esphal.cpp#L275-L287 (the original idea from esphome)
+ // - https://github.com/arendst/Tasmota/blob/217addc2bb2cf46e7633c93e87954b245cb96556/tasmota/settings.ino#L218-L262 (specific checks, which succeed when finding 0xffffffff as version)
+ // - https://github.com/arendst/Tasmota/blob/0dfa38df89c8f2a1e582d53d79243881645be0b8/tasmota/i18n.h#L780-L782 (constants)
+ std::atomic_thread_fence(std::memory_order_relaxed);
+ volatile uint32_t magic[3] [[gnu::unused]] {
+ 0x5AA55AA5,
+ 0xFFFFFFFF,
+ 0xA55AA55A
+ };
+
+ // ref. https://github.com/arendst/Tasmota/blob/217addc2bb2cf46e7633c93e87954b245cb96556/tasmota/settings.ino#L24
+ // We will certainly find these when rebooting from Tasmota. Purge SDK as well, since we may experience WDT after starting up the softAP
+ auto* rtcmem = reinterpret_cast<volatile uint32_t*>(RTCMEM_ADDR);
+ if ((0xA55A == rtcmem[64]) && (0xA55A == rtcmem[68])) {
+ DEBUG_MSG_P(PSTR("[OTA] Detected TASMOTA OTA, resetting the device...\n"));
+ rtcmem[64] = rtcmem[68] = 0;
+ customResetReason(CUSTOM_RESET_TERMINAL);
+ resetSettings();
+ eraseSDKConfig();
+ *((int*) 0) = 0;
+ // noreturn, we simply reboot after writing into 0
+ }
+
+ // TODO: also check for things throughout the flash sector, somehow?
+ }
+
+#if OTA_ARDUINOOTA_SUPPORT
+ arduinoOtaSetup();
+#endif
+#if OTA_CLIENT != OTA_CLIENT_NONE
+ otaClientSetup();
+#endif
+}

code/espurna/ota.h

@@ -38,6 +38,7 @@ void otaClientSetup();
 #include <WiFiClientSecure.h>
 #endif
 
+void otaSetup();
 void otaPrintError();
 bool otaFinalize(size_t size, int reason, bool evenIfRemaining = false);