Extend CanMsg to allow to distinguish between standard and extended IDs following a <linux/can.h> inspired approach.

Author: aentinger

api/CanMsg.h

@@ -31,7 +31,12 @@ namespace arduino
 class CanMsg : public Printable
 {
 public:
-  static size_t constexpr MAX_DATA_LENGTH = 8;
+  static size_t   constexpr MAX_DATA_LENGTH = 8;
+
+  static uint32_t constexpr CAN_EFF_FLAG    = 0x80000000U;
+  static uint32_t constexpr CAN_SFF_MASK    = 0x000007FFU; /* standard frame format (SFF) */
+  static uint32_t constexpr CAN_EFF_MASK    = 0x1FFFFFFFU; /* extended frame format (EFF) */
+
 
   CanMsg(uint32_t const can_id, uint8_t const can_data_len, uint8_t const * can_data_ptr)
   : id{can_id}
@@ -68,7 +73,10 @@ class CanMsg : public Printable
     size_t len = 0;
 
     /* Print the header. */
-    len = snprintf(buf, sizeof(buf), "[%08X] (%d) : ", id, data_length);
+    if (isStandardId())
+      len = snprintf(buf, sizeof(buf), "[%03X] (%d) : ", id, data_length);
+    else
+      len = snprintf(buf, sizeof(buf), "[%08X] (%d) : ", id, data_length);
     size_t n = p.write(buf, len);
 
     /* Print the data. */
@@ -82,11 +90,45 @@ class CanMsg : public Printable
     return n;
   }
 
+
+  uint32_t getStandardId() const {
+    return (id & CAN_SFF_MASK);
+  }
+  uint32_t getExtendedId() const {
+    return (id & CAN_EFF_MASK);
+  }
+  bool isStandardId() const {
+    return ((id & CAN_EFF_FLAG) == 0);
+  }
+  bool isExtendedId() const {
+    return ((id & CAN_EFF_FLAG) == CAN_EFF_FLAG);
+  }
+
+
+  /*
+   * CAN ID semantics (mirroring definition by linux/can.h):
+   * |- Bit   31 : frame format flag (0 = standard 11 bit, 1 = extended 29 bit)
+   * |- Bit   30 : reserved (future remote transmission request flag)
+   * |- Bit   29 : reserved (future error frame flag)
+   * |- Bit 0-28 : CAN identifier (11/29 bit)
+   */
   uint32_t id;
   uint8_t  data_length;
   uint8_t  data[MAX_DATA_LENGTH];
 };
 
+/**************************************************************************************
+ * FREE FUNCTIONS
+ **************************************************************************************/
+
+static uint32_t CanStandardId(uint32_t const id) {
+  return (id & CanMsg::CAN_SFF_MASK);
+}
+
+static uint32_t CanExtendedId(uint32_t const id) {
+  return (CanMsg::CAN_EFF_FLAG | (id & CanMsg::CAN_EFF_MASK));
+}
+
 /**************************************************************************************
  * NAMESPACE
  **************************************************************************************/