atmel-samd: Add Micro Trace Buffer support to the debug build.

tannewt · tannewt · commit 1fa4c20c2726 · 2016-10-04T16:13:33.000-07:00
The Micro Trace Buffer records the history of the pc and can be used
to debug hard faults even when the stack trace is useless.
diff --git a/atmel-samd/Makefile b/atmel-samd/Makefile
@@ -92,8 +92,10 @@ CFLAGS_CORTEX_M0 = \
 CFLAGS = $(INC) -Wall -Werror -ansi -std=gnu99 -nostdlib $(CFLAGS_CORTEX_M0) $(COPT)
 
 #Debugging/Optimization
+# TODO(tannewt): Figure out what NDEBUG does. Adding it to the debug build
+# reduces code size pretty dramatically.
 ifeq ($(DEBUG), 1)
-CFLAGS += -Os -ggdb
+CFLAGS += -Os -ggdb -DNDEBUG -DENABLE_MICRO_TRACE_BUFFER
 else
 CFLAGS += -Os -DNDEBUG
 endif
diff --git a/atmel-samd/asf/sam0/utils/cmsis/samd21/source/gcc/startup_samd21.c b/atmel-samd/asf/sam0/utils/cmsis/samd21/source/gcc/startup_samd21.c
@@ -41,6 +41,8 @@
  *
  */
 
+#include <stdbool.h>
+
 #include "samd21.h"
 
 /* Initialize segments */
@@ -65,7 +67,7 @@ void Dummy_Handler(void);
 
 /* Cortex-M0+ core handlers */
 void NMI_Handler             ( void ) __attribute__ ((weak, alias("Dummy_Handler")));
-void HardFault_Handler       ( void ) __attribute__ ((weak, alias("Dummy_Handler")));
+void HardFault_Handler( void ) __attribute__( ( naked ) );
 void SVC_Handler             ( void ) __attribute__ ((weak, alias("Dummy_Handler")));
 void PendSV_Handler          ( void ) __attribute__ ((weak, alias("Dummy_Handler")));
 void SysTick_Handler         ( void ) __attribute__ ((weak, alias("Dummy_Handler")));
@@ -269,14 +271,24 @@ void Reset_Handler(void)
         main();
 
         /* Infinite loop */
-        while (1);
+        while (true);
+}
+
+void HardFault_Handler(void)
+{
+#ifdef ENABLE_MICRO_TRACE_BUFFER
+    // Turn off the micro trace buffer so we don't fill it up in the infinite
+    // loop below.
+    REG_MTB_MASTER = 0x00000000 + 6;
+#endif
+    while(true) {}
 }
 
 /**
  * \brief Default interrupt handler for unused IRQs.
  */
 void Dummy_Handler(void)
 {
-        while (1) {
+        while (true) {
         }
 }
diff --git a/atmel-samd/main.c b/atmel-samd/main.c
@@ -270,7 +270,19 @@ void MP_WEAK __assert_func(const char *file, int line, const char *func, const c
 
 struct usart_module usart_instance;
 
+#ifdef ENABLE_MICRO_TRACE_BUFFER
+#define TRACE_BUFFER_SIZE 256
+__attribute__((__aligned__(TRACE_BUFFER_SIZE * sizeof(uint32_t)))) uint32_t mtb[TRACE_BUFFER_SIZE];
+#endif
+
 void samd21_init(void) {
+#ifdef ENABLE_MICRO_TRACE_BUFFER
+    memset(mtb, 0, sizeof(mtb));
+    // AWIDTH is 15.
+    REG_MTB_POSITION = ((uint32_t) (mtb - REG_MTB_BASE)) & 0xFFFFFFF8;
+    REG_MTB_FLOW = ((uint32_t) mtb + TRACE_BUFFER_SIZE * sizeof(uint32_t)) & 0xFFFFFFF8;
+    REG_MTB_MASTER = 0x80000000 + 6;
+#endif
     irq_initialize_vectors();
     cpu_irq_enable();
 
