UAVCAN DSDL介绍

原文：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

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]);