OS服务——SMP协议规范——SMP协议规范
本摘要总结了mcumgr库中使用的简单管理协议（SMP）及其相关机制：
SMP协议：作为mcumgr库的核心机制，用于将请求传递给设备并接收响应。
信封结构：每个帧由头（包括数据长度字段）和数据组成；支持碎片化传输时可重组目的。
操作代码：包含4个操作码（0-3），分别表示读取请求/读取响应/写入请求/写入响应。
管理组ID：分为预定义和自定义组（如默认/操作系统管理组），通常CBOR编码。
最小响应：所有请求均应返回CBOR目录结构的最小响应；若对方无SMP服务或设备无应答则允许缺少。
状态/错误代码：包括10种可能的状态码（如无误、超时等），由Zephyr用MGMTERR前缀扩展支持。
应用支持：当前仅限于Zephyr官方文档中列出的支持范围内的管理小组与操作码。
SMP协议规范
该协议旨在简明扼要地阐述SMP的基本功能。其中，在该模块中通过...的形式实现了资源数据与设备间的高效交互。
SMP是一个应用程序层协议。底层传输层不在本文档的范围内。
框架：信封
每个帧由前导部分以及后续数据构成。当传输层协议支持碎片化时，报告头中的'数据长度'字段可用于重组目的。该编码方案标记为'大编码'(即网络编码)，其中各字段均包含多于一个字节，并采用如下格式：
| 3 | 2 | 1 | 0 | ||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| Res | OP | Flags | Data Length | ||||||||||||||||||||||||||||
| Group ID | Sequence Num | Command ID | |||||||||||||||||||||||||||||
| Data … |
注意：
最初提出的规范规定
该系统支持可选的数据输入，在数据长度为零的情况下则不再存在。各组别或个体的数据编码将依据其group/ID目标来确定。
其中，字段的含义为：
| Field | Description |
|---|---|
| Res | This is reserved, not-used field and should be always set to 0. |
| OP | Operation code |
| Flags | Reserved for flags; there are no flags defined yet, the field should be set to 0 |
| Data Length | Length of the Data field |
| Group ID | Management Group ID’s |
| Sequence Num | This is a frame sequence number. The number is increased by one with each request frame. The Sequence Num of a response should match the one in the request. |
| Command ID | This is a command, within Group. |
| Data | This is data payload of the Data Length size. It is optional as Data Length may be set to zero, which means that no data follows the header. |
注意：
数据的内容取决于OP、组ID和命令ID的值。
注意：
Res字段可能会被Zephyr重新用于协议版本。
操作代码
操作代码决定了相关信息是要传输至设备还是由设备发起请求，并且需要检查数据包中是否有来自SMP服务器的发包请求或者来自该服务器的数据包响应。
已定义了以下操作代码。
| Decimal ID | Operation |
|---|---|
| 0 | read request |
| 1 | read response |
| 2 | write request |
| 3 | write response |
管理组ID
SMP 协议包含预先配置的标准群组，并提供给用户自定义群组的机会。表格列举了常见的群组
| Decimal ID | Group description |
|---|---|
| 0 | Default/OS Management Group |
| 1 | Application/software image management group |
| 2 | Statistics management |
| 3 | Application/system configuration (currently not used by Zephyr) |
| 4 | Application/system log management (currently not used by Zephyr) |
| 5 | Run-time tests (unused by Zephyr) |
| 6 | Split image management (unused by Zephyr) |
| 7 | Test crashing application (unused by Zephyr) |
| 8 | File management |
| 9 | Shell management |
| 63 | Zephyr specific basic commands group |
| 64 | This is the base group for defining an application specific management groups. |
上述组的有效载荷通常为CBOR编码方案。其中64及以上范围内的各组参数值由应用程序开发者根据需求自行设定；同时在本文文档中并未对这些参数值的具体取值进行明确的规定。
最小响应
不论您发出何种指令，在请求的另一端存在SMP客户端的情况下，请务必返回包含头信息以及CBOR映射容器的响应数据包。仅在没有任何SMP服务可用或者设备未能有效响应时才允许缺少响应数据包。
最小响应SMP数据
最小的响应是CBOR目录：
{
(str)"rc" : (int)
}这里
| “rc” | Status/error codes in responses |
|---|
响应中的状态/错误代码
| Decimal ID | Meaning |
|---|---|
| 0 | No error, OK. |
| 1 | Unknown error. |
| 2 | Not enough memory; this error is reported when there is not enough memory to complete response. |
| 3 | Invalid value; a request contains an invalid value. |
| 4 | Timeout; the operation for some reason could not be completed in assumed time. |
| 5 | No entry; the error means that request frame has been missing some information that is required to perform action. It may also mean that requested information is not available. |
| 6 | Bad state; the error means that application or device is in a state that would not allow it to perform or complete a requested action. |
| 7 | Response too long; this error is issued when buffer assigned for gathering response is not big enough. |
| 8 | Not supported; usually issued when requested Group ID or Command ID is not supported by application. |
| 9 | Corrupted payload received. |
| 10 | Device is busy with processing previous SMP request and may not process incoming one. Client should re-try later. |
| 256 | This is base error number of user defined error codes. |
Zephyr依赖于位于头文件subsys/mgmt/mcumgr/lib/mgmt/include/mgmt/mgmt.h中的MGMT_ERR_前缀定义来实现相关的功能。
由Zephyr支持的管理小组的规范
- 操作系统相关的默认配置设置
- 应用软件的镜像及安装包管理
- 数据统计与分析功能模块
- 文件存储与访问权限配置
- 脚本执行与命令行参数配置