phydat: add verbose unit_to_str function

sys/include/phydat.h

@@ -35,6 +35,7 @@
 #ifndef PHYDAT_H
 #define PHYDAT_H
 
+#include <stddef.h>
 #include <stdint.h>
 #include "kernel_defines.h"
 
@@ -179,6 +180,23 @@ void phydat_dump(phydat_t *data, uint8_t dim);
  */
 const char *phydat_unit_to_str(uint8_t unit);
 
+/**
+ * @brief   Return a string representation for every unit, including
+ *          non-physical units like 'none' or 'time'
+ *
+ * This function is useful when converting phydat_t structures to non-binary
+ * representations like JSON or XML.
+ *
+ * In practice, this function extends phydat_unit_to_str() with additional
+ * identifiers for non physical units.
+ *
+ * @param[in] unit      unit to convert
+ *
+ * @return  string representation of given unit
+ * @return  empty string ("") if unit was not recognized
+ */
+const char *phydat_unit_to_str_verbose(uint8_t unit);
+
 /**
  * @brief   Convert the given scale factor to an SI prefix
  *

sys/phydat/phydat_str.c

@@ -133,6 +133,19 @@ const char *phydat_unit_to_str(uint8_t unit)
     }
 }
 
+const char *phydat_unit_to_str_verbose(uint8_t unit)
+{
+    switch (unit) {
+        case UNIT_UNDEF:    return "undefined";
+        case UNIT_NONE:     /* fall through */
+        case UNIT_BOOL:
+            return "none";
+        case UNIT_TIME:     return "time";
+        case UNIT_DATE:     return "date";
+        default:            return phydat_unit_to_str(unit);
+    }
+}
+
 char phydat_prefix_from_scale(int8_t scale)
 {
     switch (scale) {