From c9c5d691e1bc8d66be28544863d365cb2549639a Mon Sep 17 00:00:00 2001
From: De-Backer <De-Backer@users.noreply.github.com>
Date: Thu, 17 Jun 2021 20:12:30 +0200
Subject: [PATCH] store MCUSR into R2 on bootup (#2)

* Add store MCUSR into R2 on bootup

This makes it possible to find the MCU reset caused in run code.
Because the MCUSR is being erased by the bootloader.
---
 src/bootloader.cpp | 31 +++++++++++++++++++++++++++----
 src/config.h       | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 4 deletions(-)

diff --git a/src/bootloader.cpp b/src/bootloader.cpp
index 01dddfc..2b999b9 100644
--- a/src/bootloader.cpp
+++ b/src/bootloader.cpp
@@ -47,11 +47,21 @@ MCP2515 mcp2515;
  */
 void get_mcusr(void) __attribute__((naked)) __attribute__((used)) __attribute__((section(".init3")));
 void get_mcusr(void) {
-  #if defined(MCUCSR)
-    MCUCSR = 0;
-  #else
-    MCUSR = 0;
+#if defined(MCUCSR)
+  #if MCUSR_TO_R2
+    __asm__ __volatile__(
+        "  mov r2, %[reset_caused_by_val] ;Move Between Registers \n\t" 
+        ::[reset_caused_by_val] "r"(MCUCSR));
+  #endif
+  MCUCSR = 0;
+#else
+  #if MCUSR_TO_R2
+    __asm__ __volatile__(
+        "  mov r2, %[reset_caused_by_val] ;Move Between Registers \n\t"
+        ::[reset_caused_by_val] "r"(MCUSR));
   #endif
+  MCUSR = 0;
+#endif
   wdt_disable();
 }
 
@@ -59,6 +69,11 @@ void get_mcusr(void) {
  * The main function of the bootloader.
  */
 int main () {
+  #if MCUSR_TO_R2
+    uint8_t reset_caused_by=0x00;/* MCUSR from bootloader */
+    __asm__ __volatile__("  mov %[reset_caused_by_val],r2 ;Move Between Registers \n\t"
+                         :[reset_caused_by_val] "=r" (reset_caused_by));
+  #endif
   // call init from arduino framework to setup timers
   init();
 
@@ -341,6 +356,10 @@ int main () {
             // delay for 50ms to let the mcp send the message
             delay(50);
 
+            #if MCUSR_TO_R2
+              __asm__ __volatile__("  mov r2,%[reset_caused_by_val] ;Move Between Registers \n\t"
+                         ::[reset_caused_by_val] "r" (reset_caused_by));
+            #endif
             startApp();
 
           } else if (canMsg.data[CAN_DATA_BYTE_CMD] == CMD_FLASH_DONE_VERIFY) {
@@ -372,6 +391,10 @@ int main () {
             // delay for 50ms to let the mcp send the message
             delay(50);
 
+            #if MCUSR_TO_R2
+              __asm__ __volatile__("  mov r2,%[reset_caused_by_val] ;Move Between Registers \n\t"
+                         ::[reset_caused_by_val] "r" (reset_caused_by));
+            #endif
             startApp();
           }
         }
diff --git a/src/config.h b/src/config.h
index 4af5a45..30b120d 100644
--- a/src/config.h
+++ b/src/config.h
@@ -38,6 +38,43 @@
  */
 #define TIMEOUT 250
 
+/**
+ * store The MCU Status Register to Register 2
+ * The MCU Status Register provides information on which reset source
+ * caused an MCU reset.
+ *
+ * paste this code into your program (not the bootloader)
+ * \code
+ *  uint8_t mcusr __attribute__ ((section (".noinit")));//<= the MCU Status Register
+ *  void getMCUSR(void) __attribute__((naked)) __attribute__((section(".init0")));
+ *  void getMCUSR(void)
+ *  {
+ *      __asm__ __volatile__ ( "mov %0, r2 \n" : "=r" (mcusr) : );
+ *  }
+ * \endcode
+ *
+ * to use
+ * \code
+ *  mcusr;//<= the MCU Status Register (global variable)
+ * \endcode
+ *
+ * or
+ *
+ * \code
+ *  void main()
+ *  {
+ *      uint8_t mcusr;
+ *      __asm__ __volatile__ ( "mov %0, r2 \n" : "=r" (mcusr) : );
+ *  }
+ * \endcode
+ *
+ * to use
+ * \code
+ *  mcusr;//<= the MCU Status Register (local variable in function main)
+ * \endcode
+ */
+#define MCUSR_TO_R2 1
+
 /**
  * Data rate of the CAN bus.
  * CAN_5KBPS, CAN_10KBPS, CAN_20KBPS, CAN_31K25BPS, CAN_33KBPS, CAN_40KBPS,