使用多个邮箱，需要多次调用 CAN_sendMessage函数，如下
CAN_sendMessage(CANA_BASE, TX_MSG_OBJ_ID1, MSG_DATA_LENGTH, txMsgData1);
CAN_sendMessage(CANA_BASE, TX_MSG_OBJ_ID2, MSG_DATA_LENGTH, txMsgData2);
CAN_sendMessage(CANA_BASE, TX_MSG_OBJ_ID3, MSG_DATA_LENGTH, txMsgData3);
是否要判断发送完成状态？如何判断？
但是CAN_sendMessage函数中已经有如下语句，是否不需要外加判断？可以连续写can_sendmessage?
//
// Wait for busy bit to clear
//
while((HWREGH(base + CAN_O_IF1CMD) & CAN_IF1CMD_BUSY) == CAN_IF1CMD_BUSY)
{
}
