The Crazyradio dongle is based on a Nordic semiconductor nRF24LU1 chip. The radio communication is done using the Nordic “Enhanced ShockBurst™” packet protocol in PTX mode with acknoledge. Variable size packet, from 1 to 32 bytes, can be send and acknoledged by the copter. The acknoledgement packet can contains a payload from 0 to 32Bytes.

This page document the protocol used in the version 0.40 of the Crazyradio dongle. Future version (up to 1.0) will be kept compatible.

The USB devices have the VID/PID couple 0x1915/0x7777.

Crazyradio vendor requests summary:

The nrf24L chips provides 126 Channels of 1MHz from 2400MHz to 2525MHz. The channel parameter shall be between 0 and 125 (if not the command will be ignored).

The radio channel is set as soon as the setup transaction is completed which takes about 1ms. The new frequency is going to be used for the following transfered packets. Default value for the radio channel is 2.

The packet sent by the radio contains a 5 bytes address. The same address must be configured in the receiver for the communication to work.

The address must follow the requirement of the section 6.4.3.2 of the nRF24LU1 documentation:

Addresses where the level shifts only one time (that is, 000FFFFFFF) can often be detected in
noise and can give a false detection, which may give a raised Packet-Error-Rate. Addresses
as a continuation of the preamble (hi-low toggling) raises the Packet-Error-Rate.

The default address is 0xE7E7E7E7E7.

Possible values for the datarate:

After sending a packet the radio automatically waits for an acknowledge. ARD and ARC permits to configure the delay the radio waits for the acknowledge and the number of time the transfer will be retried in case the acknowledge is not received in that delay.

The delay ARD depends of the length, in second, of the ack packed. This depends of the datarate and the Payload length contained in the Ack packet. The ARD can be configured either by step of 250us or by ack payload length. If the ack payload length is configured the time will be recalculated automatically even if the datarate is changed. To set the Ack payload lenght the bit 7 of Ard must be set (length | 0x80)

Possible values for ARD:

ARC configures the number of time the radio will retry a transfer if the Ack has not been received, it can be set from 0 to 15.

By default ARD=32Bytes (0xA0) and ARC=3.

The radio dongle is configured in PTX mode (in the Nordic terminology) which means that it sends packet to the copter and waits for the acknowledge. The acknowledge can contains a Payload which is the mean to get data from the copter.

The packet is to send is sent to the EP1 and the ack status is then received from the EP1. There are no buffering in the radio dongle, the ACK must be received by the PC before the next packet can be sent.

This protocol permits to transfer about 500 packets per seconds.