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:

Port	Channel	Function
2	0	TOC access
2	1	Parameter read
2	2	Parameter write
2	3	Misc. commands

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:

Message ID	Meaning in upstream packets	Meaning in downstream packets
0	Reset TOC pointer	Last TOC element
1	Get next TOC element	TOC element (ID, type, group, name)
3	Get TOC CRC32	Number of parameters, TOC CRC32

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:

Type code	C type	Python unpack
0x08	uint8_t	'<B'
0x09	uint16_t	'<H'
0x0A	uint32_t	'<L'
0x0B	uint64_t	'<Q'
0x00	int8_t	'<b'
0x01	int16_t	'<h'
0x02	int32_t	'<i'
0x03	int64_t	'<q'
0x05	FP16	''
0x06	float	'<f'
0x07	double	'<d'

Parameter read

Byte	Request fields	Content
0	ID	ID of the parameter to read (see TOC)

Byte	Answer fields	Content
0	ID	ID of the parameter
1-..	value	Value of the parameter. Size and format is described in the TOC

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

Parameter write

Byte	Request fields	Content
0	ID	ID of the parameter to write
1-…	value	Value to write. Size and format is described in the TOC

Byte	Answer fields	Content
0	ID	ID of the parameter
1-…	value	Value of the parameter. Size and format is described in the TOC

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:

Code	Command
0x00	Set by name

Set by name

Byte	Request fields	Content
0	SET_BY_NAME	0x00
1-n	group	Name of the group
n-(n+1)	NULL	0
(n+1)-(n+m+1)	name	Name of the parameter
(n+m+1)-(n+m+2)	NULL	0
(n+m+2)-(n+m+3)	TYPE	Parameter type
(n+m+3)-…	value	Value. Size and format is described by type

Byte	Answer fields	Content
0	SET_BY_NAME	0x00
1-n	group	Name of the group
n-(n+1)	NULL	0
(n+1)-(n+m+1)	name	Name of the parameter
(n+m+2)	NULL	0
(n+m+3)	ERROR	0 if the parameter has been successfully written. Other code are taken fromerrno C codes.

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.