UAVCAN DSDL介绍

骑猪看日落 2022-05-29 08:29 291阅读 0赞

`原文`：[http://uavcan.org/Specification/3.\_Data\_structure\_description\_language/][http_uavcan.org_Specification_3._Data_structure_description_language]

`DSDL`：Data structure description language

实际上，就是自动生成的C++格式的数据结构。用来定义UAVCAN中的各种类型的消息。个人认为就是看着更清晰，理解起来更容易，也是UAVCAN的设计思想。使用C代码也很容易实现

`C代码例子`：[https://github.com/zwx230741/libcanard][https_github.com_zwx230741_libcanard]

**结构定义**

[default data type ID.]<data type name>.uavcan

+ uavcan                        <-- Root namespace
        + equipment                 <-- Nested namespace
            + ...
        + protocol                  <-- Nested namespace
            + 341.NodeStatus.uavcan <-- Definition of data type "uavcan.protocol.NodeStatus" with 
                                        default data type ID 341
            + ...
        + Timestamp.uavcan          <-- Definition of data type "uavcan.Timestamp", default data 
                                        type ID is not assigned

DSDL中定义的都是标准的数据类型，也是默认的数据类型，不需要更改  
可用的数据类型ID是有限的

**DSDL发布消息**  
具体源码可以参考UAVCAN源码  
DSDL通过Publisher来发布消息，当你需要发送数据到can设备时使用

uavcan::equipment::esc::RawCommand msg;
    uavcan::Publisher<uavcan::equipment::esc::RawCommand>           _uavcan_pub_raw_cmd;
    (void)_uavcan_pub_raw_cmd.broadcast(msg); //广播消息

**DSDL订阅消息**  
DSDL通过Subscriber来订阅消息，当你需要接收can设备数据到时使用

typedef uavcan::MethodBinder<UavcanEscController*,
            void (UavcanEscController::*)(const uavcan::ReceivedDataStructure<uavcan::equipment::esc::Status>&)>
            StatusCbBinder;
    uavcan::Subscriber<uavcan::equipment::esc::Status, StatusCbBinder>  _uavcan_sub_status;
    
    int res = _uavcan_sub_status.start(StatusCbBinder(this, &UavcanEscController::esc_status_sub_cb));
    if (res < 0)
    {
        warnx("ESC status sub failed %i", res);
        return res;
    }
    
    void UavcanEscController::esc_status_sub_cb(const uavcan::ReceivedDataStructure<uavcan::equipment::esc::Status> &msg)
    {
        ;
    }

**数据结构举例**

#
    # Abstract node status information.
    #
    # Any UAVCAN node is required to publish this message periodically.
    #
    
    #
    # Publication period may vary within these limits.
    # It is NOT recommended to change it at run time.
    #
    uint16 MAX_BROADCASTING_PERIOD_MS = 1000
    uint16 MIN_BROADCASTING_PERIOD_MS = 2
    
    #
    # If a node fails to publish this message in this amount of time, it should be considered offline.
    #
    uint16 OFFLINE_TIMEOUT_MS = 3000
    
    #
    # Uptime counter should never overflow.
    # Other nodes may detect that a remote node has restarted when this value goes backwards.
    #
    uint32 uptime_sec
    
    #
    # Abstract node health.
    #
    uint2 HEALTH_OK         = 0     # The node is functioning properly.
    uint2 HEALTH_WARNING    = 1     # A critical parameter went out of range or the node 
                                      encountered a minor failure.
    uint2 HEALTH_ERROR      = 2     # The node encountered a major failure.
    uint2 HEALTH_CRITICAL   = 3     # The node suffered a fatal malfunction.
    uint2 health
    
    #
    # Current mode.
    #
    # Mode OFFLINE can be actually reported by the node to explicitly inform other network
    # participants that the sending node is about to shutdown. In this case other nodes will not
    # have to wait OFFLINE_TIMEOUT_MS before they detect that the node is no longer available.
    #
    # Reserved values can be used in future revisions of the specification.
    #
    uint3 MODE_OPERATIONAL      = 0         # Node is performing its main functions.
    uint3 MODE_INITIALIZATION   = 1         # Node is initializing; this mode is entered 
                                              immediately after startup.
    uint3 MODE_MAINTENANCE      = 2         # Node is under maintenance.
    uint3 MODE_SOFTWARE_UPDATE  = 3         # Node is in the process of updating its software.
    uint3 MODE_OFFLINE          = 7         # Node is no longer available.
    uint3 mode
    
    #
    # Not used currently, keep zero when publishing, ignore when receiving.
    #
    uint3 sub_mode
    
    #
    # Optional, vendor-specific node status code, e.g. a fault code or a status bitmask.
    #
    uint16 vendor_specific_status_code

结构体中的属性值：  
默认值：不可以修改，也不参与网络交互  
变量：可以通过应用程序修改，参与网络收发

uint8[<=64] payload

UAVCAN支持不定长数组，使用起来很方便。但是要注意，DSDL订阅消息的时候，默认第一个字节表示数组的长度

服务响应标记：  
该标记由三个减号组成

---

**C方式发送消息**  
等价于`DSDL发布消息`

/* 封包数据，根据数据类型 void canardEncodeScalar(void *destination, uint32_t bit_offset, uint8_t bit_length, //bit长度 const void *value) */
    canardEncodeScalar(buffer,  0, 28, &uptime_sec);
    
    /* 发送消息，加入到发送队列 int canardBroadcast(CanardInstance *ins, uint64_t data_type_signature, uint16_t data_type_id, uint8_t *inout_transfer_id, uint8_t priority, const void *payload, uint16_t payload_len) */
    canardBroadcast(&canard, UAVCAN_NODE_STATUS_DATA_TYPE_SIGNATURE,
                   UAVCAN_NODE_STATUS_DATA_TYPE_ID, &transfer_id, CANARD_TRANSFER_PRIORITY_LOW,
                   buffer, UAVCAN_NODE_STATUS_MESSAGE_SIZE);

**C方式接收消息**  
等价于`DSDL订阅消息`

/* 从接收到的数据包中，解析出数据 int canardDecodeScalar(const CanardRxTransfer *transfer, uint32_t bit_offset, uint8_t bit_length, bool value_is_signed, void *out_value) */
    canardDecodeScalar(transfer, 0, 28, false, &uptime_sec[i]);

[http_uavcan.org_Specification_3._Data_structure_description_language]: http://uavcan.org/Specification/3._Data_structure_description_language/
[https_github.com_zwx230741_libcanard]: https://github.com/zwx230741/libcanard