Parameters

The parameters system makes all the gettable and settable parameters of the copter accessible. The copter holds a table of parameters which can be retrieved. In this table every parameter name is associated with an ID and a group name. Three IDs are used to acces the TOC and the parameters:

TOC access

These messages permit to access the parameters table of content. The first byte of the message is a message ID, three messages ID are defined:

The upstream ID are commands and are sent alone. The downstream has the following formats:

Bytes     1       1          1    Null terminated strings
        +---+------------+------+----------+--------------+
        | 0 |            |      |          |              |
        +---+  Param ID  | Type |  Group   |     Name     |
        | 1 |            |      |          |              |
        +---+------------+------+---+------+--------------+
        | 3 | Num. Param |  CRC32   |
        +---+------------+----------+
Bytes     1       1           4

The parameters are sequentially requested by the PC until the end. When the last parameter is reached it has the ID 0 'Last TOC element'. The reset command permits to reset the TOC pointers so that the next sent TOC element will be the first one. The "Get TOC CRC" command also returns the number of parameters.

The CRC32 is a hash of the copter TOC. This is aimed at implementing caching of the TOC in the PC Utils to avoid fetching the full TOC each time the copter is connected.

The type is one byte describing the parameter type:

Parameter read

The read request is a simple packet on channel 1. Crazyflie answers with the value.

Parameter write

The write request is a simple packet on channel 2. Crazyflie sends back the parameter value as an acknowledgement.

Misc. commands

The following misc commands are implemented:

Set by name

Group and name are ascii strings of size respectively n and m. The type corresponds to the TOC type of the parameter. It is checked for consistency.

This command is useful to set a parameter without having to fetch the full TOC. It is enough to know the group, name and type of the parameter to write it.

Value updated

There is no request packet for this message, it is only sent by the Crazyflie.

This packet is send by the Crazyflie when a parameters has been modified in the firmware. This can for example happen when an app is controlling the Crazyflie autonomously.

Get extended type

Deprecated: Use Get extended type V2 (0x07) instead. This command may have ambiguous responses if the extended_type value equals an error code (e.g., ENOENT=2). Currently not an issue (only extended_type=1 exists), but the V2 command provides an unambiguous format.

Get the extended type of a parameter.

The extended type describes extended properties of the parameter. Currently only one extended type is available.

Persistent store

Store the current value of a parameter to persistent storage. The parameter will be set to this value. after reboot.

Persistent get state

Get the persistence state of a parameter.

ts == the type size, described in the TOC

If the result is an error (0x02) the packet is terminated after 4 bytes.

Persistent clear

Clear the persistent data for a parameter. After reboot the parameter will be set to the default value.

Get default value

Deprecated: Use Get default value V2 (0x08) instead. This command has ambiguous responses for U8 parameters with default value 2 (ENOENT).

Get the default value of a parameter. The default value is the value the parameter has at startup if not overridden by persistent storage.

Protocol ambiguity: For U8 parameters with default value 2, the success response [0x06, ID_L, ID_H, 0x02] is identical to the error response with ENOENT. Clients should check the packet size to distinguish, or preferably use the V2 command.

Get extended type V2

This command provides unambiguous responses compared to the deprecated Get extended type (0x02).

Get the extended type of a parameter with an explicit status byte.

The status byte (byte 3) allows clients to distinguish success from error unambiguously. On error, the packet is 4 bytes. On success, the packet is 5 bytes with the extended type in byte 4.

Get default value V2

This command provides unambiguous responses compared to the deprecated Get default value (0x06).

Get the default value of a parameter with an explicit status byte.

The status byte (byte 3) allows clients to distinguish success from error unambiguously. On error, the packet is 4 bytes. On success, the packet is 4 + parameter_size bytes with the default value starting at byte 4.