From c49fe825906adb48643d2052a6749d7566c15493 Mon Sep 17 00:00:00 2001
From: Jason2866 <24528715+Jason2866@users.noreply.github.com>
Date: Sat, 29 Jun 2024 16:10:51 +0200
Subject: [PATCH] PWM NMI fix

---
 cores/esp8266/core_esp8266_waveform_pwm.cpp | 36 ++++++++++++++++++++-
 cores/esp8266/core_version.h                |  6 ++--
 package.json                                |  2 +-
 3 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/cores/esp8266/core_esp8266_waveform_pwm.cpp b/cores/esp8266/core_esp8266_waveform_pwm.cpp
index aea88e15b9..ebb6c4ac2a 100644
--- a/cores/esp8266/core_esp8266_waveform_pwm.cpp
+++ b/cores/esp8266/core_esp8266_waveform_pwm.cpp
@@ -1,3 +1,7 @@
+/* Modified to work around a fault in the NMI handling, which
+   can result in the system locking up and hard WDT crashes.
+*/
+
 /*
   esp8266_waveform - General purpose waveform generation and control,
                      supporting outputs on all pins in parallel.
@@ -44,8 +48,12 @@
 #include "ets_sys.h"
 #include "core_esp8266_waveform_pwm.h"
 #include "user_interface.h"
+
 extern "C" {
 
+// Linker magic
+void usePWMFixedNMI() {};
+
 // Maximum delay between IRQs
 #define MAXIRQUS (10000)
 
@@ -436,6 +444,30 @@ static inline ICACHE_RAM_ATTR uint32_t earliest(uint32_t a, uint32_t b) {
     return (da < db) ? a : b;
 }
 
+// NMI crash workaround
+// Sometimes the NMI fails to return, stalling the CPU.  When this happens,
+// the next NMI gets a return address /inside the NMI handler function/.
+// We work around this by caching the last NMI return address, and restoring
+// the epc3 and eps3 registers to the previous values if the observed epc3
+// happens to be pointing to the _NMILevelVector function.
+extern void _NMILevelVector();
+extern void _UserExceptionVector_1(); // the next function after _NMILevelVector
+static inline ICACHE_RAM_ATTR void nmiCrashWorkaround() {
+  static uintptr_t epc3_backup, eps3_backup;
+
+  uintptr_t epc3, eps3;
+  __asm__ __volatile__("rsr %0,epc3; rsr %1,eps3":"=a"(epc3),"=a" (eps3));
+  if ((epc3 < (uintptr_t) &_NMILevelVector) || (epc3 >= (uintptr_t) &_UserExceptionVector_1)) {
+    // Address is good; save backup
+    epc3_backup = epc3;
+    eps3_backup = eps3;
+  } else {
+    // Address is inside the NMI handler -- restore from backup
+    __asm__ __volatile__("wsr %0,epc3; wsr %1,eps3"::"a"(epc3_backup),"a"(eps3_backup));
+  }
+}
+
+
 // The SDK and hardware take some time to actually get to our NMI code, so
 // decrement the next IRQ's timer value by a bit so we can actually catch the
 // real CPU cycle counter we want for the waveforms.
@@ -452,9 +484,11 @@ static inline ICACHE_RAM_ATTR uint32_t earliest(uint32_t a, uint32_t b) {
 #endif
 
 // When the time to the next edge is greater than this, RTI and set another IRQ to minimize CPU usage
-#define MINIRQTIME microsecondsToClockCycles(4)
+#define MINIRQTIME microsecondsToClockCycles(6)
 
 static ICACHE_RAM_ATTR void timer1Interrupt() {
+  nmiCrashWorkaround();
+
   // Flag if the core is at 160 MHz, for use by adjust()
   bool turbo = (*(uint32_t*)0x3FF00014) & 1 ? true : false;
 
diff --git a/cores/esp8266/core_version.h b/cores/esp8266/core_version.h
index 7db6da5824..317328b1b7 100644
--- a/cores/esp8266/core_version.h
+++ b/cores/esp8266/core_version.h
@@ -1,4 +1,4 @@
 #define ARDUINO_ESP8266_GIT_VER 0x3969889e
-#define ARDUINO_ESP8266_GIT_DESC 2.7.7
-#define ARDUINO_ESP8266_RELEASE_2_7_7
-#define ARDUINO_ESP8266_RELEASE "2_7_7"
+#define ARDUINO_ESP8266_GIT_DESC 2.7.8
+#define ARDUINO_ESP8266_RELEASE_2_7_8
+#define ARDUINO_ESP8266_RELEASE "2_7_8"
diff --git a/package.json b/package.json
index e1754322c9..20f02bf499 100644
--- a/package.json
+++ b/package.json
@@ -2,5 +2,5 @@
     "name": "framework-arduinoespressif8266",
     "description": "Arduino Wiring-based Framework for Tasmota (ESP8266 Core)",
     "url": "https://github.com/tasmota/Arduino",
-    "version": "2.7.7"
+    "version": "2.7.8"
 }