PX4模块设计之四十五：param模块

Posted 2022-10-03 lida2003

PX4模块设计之四十五：param模块

• 1. param模块简介
• 2. 模块入口函数param_main
• 3 重要函数列表
• 4. 总结
• 5. 参考资料

1. param模块简介

### Description
Command to access and manipulate parameters via shell or script.

This is used for example in the startup script to set airframe-specific parameters.

Parameters are automatically saved when changed, eg. with `param set`. They are typically stored to FRAM
or to the SD card. `param select` can be used to change the storage location for subsequent saves (this will
need to be (re-)configured on every boot).

If the FLASH-based backend is enabled (which is done at compile time, e.g. for the Intel Aero or Omnibus),
`param select` has no effect and the default is always the FLASH backend. However `param save/load <file>`
can still be used to write to/read from files.

Each parameter has a 'used' flag, which is set when it's read during boot. It is used to only show relevant
parameters to a ground control station.

### Examples
Change the airframe and make sure the airframe's default parameters are loaded:
$ param set SYS_AUTOSTART 4001
$ param set SYS_AUTOCONFIG 1
$ reboot

param <command> [arguments...]
 Commands:
   load          Load params from a file (overwrite all)
     [<file>]    File name (use default if not given)

   import        Import params from a file
     [<file>]    File name (use default if not given)

   save          Save params to a file
     [<file>]    File name (use default if not given)

   dump          Dump params from a file
     [<file>]    File name (use default if not given)

   select        Select default file
     [<file>]    File name

   select-backup Select default file
     [<file>]    File name

   show          Show parameter values
     [-a]        Show all parameters (not just used)
     [-c]        Show only changed params (unused too)
     [-q]        quiet mode, print only param value (name needs to be exact)
     [<filter>]  Filter by param name (wildcard at end allowed, eg. sys_*)

   show-for-airframe Show changed params for airframe config

   status        Print status of parameter system

   set           Set parameter to a value
     <param_name> <value> Parameter name and value to set
     [fail]      If provided, let the command fail if param is not found

   set-default   Set parameter default to a value
     [-s]        If provided, silent errors if parameter doesn't exists
     <param_name> <value> Parameter name and value to set
     [fail]      If provided, let the command fail if param is not found

   compare       Compare a param with a value. Command will succeed if equal
     [-s]        If provided, silent errors if parameter doesn't exists
     <param_name> <value> Parameter name and value to compare

   greater       Compare a param with a value. Command will succeed if param is
                 greater than the value
     [-s]        If provided, silent errors if parameter doesn't exists
     <param_name> <value> Parameter name and value to compare
     <param_name> <value> Parameter name and value to compare

   touch         Mark a parameter as used
     [<param_name1> [<param_name2>]] Parameter name (one or more)

   reset         Reset only specified params to default
     [<param1> [<param2>]] Parameter names to reset (wildcard at end allowed)

   reset_all     Reset all params to default
     [<exclude1> [<exclude2>]] Do not reset matching params (wildcard at end
                 allowed)

   index         Show param for a given index
     <index>     Index: an integer >= 0

   index_used    Show used param for a given index
     <index>     Index: an integer >= 0

   find          Show index of a param
     <param>     param name

注：print_usage函数是具体对应实现。

2. 模块入口函数param_main

该模块纯C语言风格，没有C++类继承或者C/C++混合的编码风格，整体看起来就很清爽。

注：C++设计一定要建模，一定要做好概念抽象。至于C/C++那种混合的编程风格，笔者是不建议的。

param_main
 ├──> <argc < 2>  // 参数不够，直接提供打印帮助!!!
 │   └──> print_usage()
 ├──> <!strcmp(argv[1], "save")> // save 子命令
 │   ├──> <argc >= 3>
 │   │   └──> do_save(argv[2])
 │   └──> <else>
 │       └──> do_save_default()
 ├──> <!strcmp(argv[1], "dump")> // dump 子命令
 │   ├──> <argc >= 3>
 │   │   └──> do_dump(argv[2])
 │   └──> <else>
 │       └──> do_dump(param_get_default_file())
 ├──> <!strcmp(argv[1], "load")> // load 子命令
 │   ├──> <argc >= 3>
 │   │   └──> do_load(argv[2])
 │   └──> <else>
 │       └──> do_load(param_get_default_file())
 ├──> <!strcmp(argv[1], "import")> // import 子命令
 │   ├──> <argc >= 3>
 │   │   └──> do_import(argv[2])
 │   └──> <else>
 │       └──> do_import()
 ├──> <!strcmp(argv[1], "select")> // select 子命令
 │   ├──> <argc >= 3>
 │   │   └──> param_set_default_file(argv[2])
 │   ├──> <else>
 │   │   └──> param_set_default_file(nullptr)
 │   ├──> const char *default_file = param_get_default_file()
 │   └──> <default_file> PX4_INFO("selected parameter default file %s", default_file)
 ├──> <!strcmp(argv[1], "select-backup")> // select-backup 子命令
 │   ├──> <argc >= 3>
 │   │   └──> param_set_backup_file(argv[2])
 │   ├──> <else>
 │   │   └──> param_set_backup_file(nullptr)
 │   ├──> const char *backup_file = param_get_backup_file()
 │   └──> <backup_file> PX4_INFO("selected parameter backup file %s", backup_file)
 ├──> <!strcmp(argv[1], "show")>  // show 子命令
 │   ├──> <argc >= 3>
 │   │   ├──> <!strcmp(argv[2], "-c")>  // optional argument -c to show only non-default params
 │   │   │    ├──> <argc >= 4>
 │   │   │    │   └──> do_show(argv[3], true)
 │   │   │    └──> <else>
 │   │   │        └──> do_show(nullptr, true)
 │   │   ├──> <!strcmp(argv[2], "-a")>
 │   │   │    └──> do_show_all()
 │   │   ├──> <!strcmp(argv[2], "-q")>
 │   │   │    └──> <argc >= 4> do_show_quiet(argv[3])
 │   │   └──> <else>
 │   │        └──> do_show(argv[2], false)
 │   └──> <else>
 │       └──> do_show(nullptr, false)
 ├──> <!strcmp(argv[1], "show-for-airframe")>  // show-for-airframe 子命令
 │   └──> do_show_for_airframe()
 ├──> <!strcmp(argv[1], "status")>  // status 子命令
 │   └──> param_print_status()
 ├──> <!strcmp(argv[1], "set")>  // set 子命令
 │   ├──> <argc >= 5>
 │   │   ├──> bool fail = !strcmp(argv[4], "fail")  //if the fail switch is provided, fails the command if not found
 │   │   └──> return do_set(argv[2], argv[3], fail)
 │   └──> <argc >= 4> do_set(argv[2], argv[3], false)
 ├──> <!strcmp(argv[1], "set-default")>  // set-default 子命令
 │   ├──> <argc >= 5 && !strcmp(argv[2], "-s")> do_set_custom_default(argv[3], argv[4], true)
 │   └──> <argc == 4> do_set_custom_default(argv[2], argv[3])
 ├──> <!strcmp(argv[1], "compare")> // compare 子命令
 │   ├──> <argc >= 5 && !strcmp(argv[2], "-s")> do_compare(argv[3], &argv[4], argc - 4, COMPARE_OPERATOR::EQUAL, COMPARE_ERROR_LEVEL::SILENT)
 │   └──> <argc >= 4> do_compare(argv[2], &argv[3], argc - 3, COMPARE_OPERATOR::EQUAL, COMPARE_ERROR_LEVEL::DO_ERROR)
 ├──> <!strcmp(argv[1], "greater")>  // greater 子命令
 │   ├──> <argc >= 5 && !strcmp(argv[2], "-s")> do_compare(argv[3], &argv[4], argc - 4, COMPARE_OPERATOR::GREATER, COMPARE_ERROR_LEVEL::SILENT)
 │   └──> <argc >= 4> do_compare(argv[2], &argv[3], argc - 3, COMPARE_OPERATOR::GREATER, COMPARE_ERROR_LEVEL::DO_ERROR)
 ├──> <!strcmp(argv[1], "reset")>  //reset 子命令
 │   └──> <argc >= 3> do_reset_specific((const char **) &argv[2], argc - 2)
 ├──> <!strcmp(argv[1], "reset_all")>  //reset_all 子命令
 │   ├──> <argc >= 3>
 │   │   └──> do_reset_all((const char **) &argv[2], argc - 2)
 │   └──> <else>
 │       └──> do_reset_all(nullptr, 0)
 ├──> <!strcmp(argv[1], "touch")>  // touch 子命令
 │   └──> <argc >= 3> do_touch((const char **) &argv[2], argc - 2)
 ├──> <!strcmp(argv[1], "index_used")>  // index_used 子命令
 │   └──> <argc >= 3> do_show_index(argv[2], true)
 ├──> <!strcmp(argv[1], "index")>  // index 子命令
 │   └──> <argc >= 3> do_show_index(argv[2], false)
 └──> <!strcmp(argv[1], "find")>  // find 子命令
     └──> <argc >= 3> do_find(argv[2])

3 重要函数列表

所有参数相关操作都是使用了Parameters API，关于全局参数存储 Parameters API这里不做展开，详见：src/lib/Parameters, param.h

1. do_save
2. do_save_default
3. do_dump
4. do_load
5. do_import
6. param_set_default_file
7. param_set_backup_file
8. do_show
9. do_show_for_airframe
10. param_print_status
11. do_set
12. do_set_custom_default
13. do_compare
14. do_reset_specific
15. do_reset_all
16. do_touch
17. do_show_index
18. do_find

4. 总结

该模块主要提供了系统参数的动态更新/固化保存，以及提供了参数修正的底层操作方法。

5. 参考资料

【1】PX4开源软件框架简明简介
【2】PX4模块设计之十一：Built-In框架
【3】PX4模块设计之十二：High Resolution Timer设计
【4】PX4模块设计之十三：WorkQueue设计
【5】PX4模块设计之十七：ModuleBase模块
【6】PX4模块设计之三十：Hysteresis类
【7】PX4 modules_main