AN3262

Communication protocol

Doc ID 17845 Rev 2

3/27

2

Communication protocol

A bootloading session consists of exchanges of commands codes and related data between

bootloader device (target) and host (transmitter) nodes. The protocol chosen for this

purpose is the same one as specified in application note AN3155 for STM32 USART

bootloader; its commands are a subset of those specified. The command set is further

described in the next section. The replacement of USART (universal

synchronous/asynchronous receiver/transmitter) with the 802.15.4 standard for point-to-

point transmission of bits over the air, implies the deployment of all the well-known features

to cope with lossy channels such as CRC check, MAC level ACK detection and packet

retries in addition to all the functions that the (higher level) protocol provides to improve the

reliability of communication as described in the next section.

Commands and data are sent in the 802.15.4 payload which is variable in size according to

the specific information to be sent. 802.15.4 packets can be sent unicast and broadcast.

Broadcast packet are supported by a subset of commands and they are useful to discover

nodes in bootloader mode.

Figure 2 shows the selected format for a unicast 802.15.4 packet.

Figure 2.

802.15.4 packet format for unicast packet transmission

Figure 3 shows the selected format for a broadcast 802.15.4 packet.

Figure 3.

802.15.4 packet format for broadcast packet transmission

The communication channel (between channels 11 and 26) and the PAN ID can be freely

chosen by the application before it launches the bootloader. In the case, where the

bootloader is not started by the application, it will run on a default channel (15) and default

bootloader PAN ID 0xB00B.

Frame

Control

(2 bytes)

0x61 0xCC

Sequence

Number

(1 byte)

Destination

Pan ID

(2 bytes)

Destination

EUI64

(8 bytes)

Source

EUI64

(8 bytes)

Payload

(variable)

FCS

(2 bytes)

Frame

Control

(2 bytes)

0x01 0xC8

Sequence

Number

(1 byte)

Destination

Pan ID

(2 bytes)

0xFFFF

Destination

Short

Address

(2 bytes)

0xFFFF

Source

EUI64

(8 bytes)

Payload

(variable)

FCS

(2 bytes)