2 files changed, 110 insertions, 0 deletions

diff --git a/build_keyboard.mk b/build_keyboard.mk
index 282adcb11..461b17cd7 100644
--- a/build_keyboard.mk
+++ b/build_keyboard.mk
@@ -180,6 +180,8 @@ ifeq ($(strip $(SERIAL_LINK_ENABLE)), yes)
         VAPTH += $(SERIAL_PATH)
 endif
 
+SRC += $(QUANTUM_DIR)/variable_trace.c
+
 # Optimize size but this may cause error "relocation truncated to fit"
 #EXTRALDFLAGS = -Wl,--relax
 
diff --git a/quantum/variable_trace.c b/quantum/variable_trace.c
new file mode 100644
index 000000000..dfa37bdef
--- /dev/null
+++ b/quantum/variable_trace.c
@@ -0,0 +1,108 @@
+#include "variable_trace.h"
+#include <stddef.h>
+#include <string.h>
+
+#ifdef NO_PRINT
+#error "You need undef NO_PRINT to use the variable trace feature"
+#endif
+
+#ifndef CONSOLE_ENABLE
+#error "The console needs to be enabled in the makefile to use the variable trace feature"
+#endif
+
+
+#define NUM_TRACED_VARIABLES 1
+#define MAX_TRACE_SIZE 4
+
+typedef struct {
+    const char* name;
+    void* addr;
+    unsigned size;
+    const char* func;
+    int line;
+    uint8_t last_value[MAX_TRACE_SIZE];
+
+} traced_variable_t;
+
+static traced_variable_t traced_variables[NUM_TRACED_VARIABLES];
+
+void add_traced_variable(const char* name, void* addr, unsigned size, const char* func, int line) {
+    verify_traced_variables(func, line);
+    if (size > MAX_TRACE_SIZE) {
+#if defined(__AVR__)
+       xprintf("Traced variable \"%S\" exceeds the maximum size %d\n", name, size);
+#else
+       xprintf("Traced variable \"%s\" exceeds the maximum size %d\n", name, size);
+#endif
+       size = MAX_TRACE_SIZE;
+    }
+    int index = -1;
+    for (int i = 0; i < NUM_TRACED_VARIABLES; i++) {
+        if (index == -1 && traced_variables[i].addr == NULL){
+            index = i;
+        }
+        else if (strcmp_P(name, traced_variables[i].name)==0) {
+            index = i;
+            break;
+        }
+    }
+
+    if (index == -1) {
+        xprintf("You can only trace %d variables at the same time\n", NUM_TRACED_VARIABLES);
+        return;
+    }
+
+    traced_variable_t* t = &traced_variables[index];
+    t->name = name;
+    t->addr = addr;
+    t->size = size;
+    t->func = func;
+    t->line = line;
+    memcpy(&t->last_value[0], addr, size);
+
+}
+
+void remove_traced_variable(const char* name, const char* func, int line) {
+    verify_traced_variables(func, line);
+    for (int i = 0; i < NUM_TRACED_VARIABLES; i++) {
+        if (strcmp_P(name, traced_variables[i].name)==0) {
+            traced_variables[i].name = 0;
+            traced_variables[i].addr = NULL;
+            break;
+        }
+    }
+}
+
+void verify_traced_variables(const char* func, int line) {
+    for (int i = 0; i < NUM_TRACED_VARIABLES; i++) {
+        traced_variable_t* t = &traced_variables[i];
+        if (t->addr != NULL && t->name != NULL) {
+            if (memcmp(t->last_value, t->addr, t->size)!=0){
+#if defined(__AVR__)
+               xprintf("Traced variable \"%S\" has been modified\n", t->name);
+               xprintf("Between %S:%d\n", t->func, t->line);
+               xprintf("And %S:%d\n", func, line);
+
+#else
+               xprintf("Traced variable \"%s\" has been modified\n", t->name);
+               xprintf("Between %s:%d\n", t->func, t->line);
+               xprintf("And %s:%d\n", func, line);
+#endif
+               xprintf("Previous value ");
+               for (int j=0; j<t->size;j++) {
+                   print_hex8(t->last_value[j]);
+               }
+               xprintf("\nNew value ");
+               uint8_t* addr = (uint8_t*)(t->addr);
+               for (int j=0; j<t->size;j++) {
+                   print_hex8(addr[j]);
+               }
+               xprintf("\n");
+               memcpy(t->last_value, addr, t->size);
+           }
+        }
+
+        t->func = func;
+        t->line = line;
+    }
+}