improve debugging on cortex m

src/nrf52/hardfault.cpp

@@ -82,8 +82,34 @@ extern "C" void HardFault_Impl(uint32_t stack[])
     // while (1) ;
 }
 
+#ifndef INC_FREERTOS_H
+// This is a generic cortex M entrypoint that doesn't assume freertos
+
 extern "C" void HardFault_Handler(void)
 {
     asm volatile(" mrs r0,msp\n"
                  " b HardFault_Impl \n");
 }
+#else
+
+/* The prototype shows it is a naked function - in effect this is just an
+assembly function. */
+extern "C"  void HardFault_Handler( void ) __attribute__( ( naked ) );
+
+/* The fault handler implementation calls a function called
+prvGetRegistersFromStack(). */
+extern "C"  void HardFault_Handler(void)
+{
+    __asm volatile
+    (
+        " tst lr, #4                                                \n"
+        " ite eq                                                    \n"
+        " mrseq r0, msp                                             \n"
+        " mrsne r0, psp                                             \n"
+        " ldr r1, [r0, #24]                                         \n"
+        " ldr r2, handler2_address_const                            \n"
+        " bx r2                                                     \n"
+        " handler2_address_const: .word HardFault_Impl    \n"
+    );
+}
+#endif