Communication

Packet based protocol

The communication between a reader and a device chain is performed using a custom packet based protocol.

The source code documentation of the packet can be found :doc:here <packet>.

Field	Encoding	Description
Method	uint8_t	Type of packet. See commands
PIC	uint16_t	Position In Chain. Index of the device in the chain
Options	uint16_t	Metadata for the packet
UID	char[25]	Universal ID of the device
Checksum	uint32_t	Checksum of the packet
Data	uint8_t[DATA_SIZE]	Actual data of the packet

The DATA_SIZE can be defined by the user, but it has to be small than the smallest SRAM size of a device in the chain.

Working with packets

Example of creation of a packet

packet = Packet() # Generate a packet with default values

# The following are the default values
packet.with_method(Method.Ping)
packet.with_options(0x0)
packet.with_checksum(0)
packet.with_pic(1)
packet.with_uid("DEVICE ID")
packet.with_data([0x0, ..., 0x0])

packet.craft() # Craft the packet to send it

# The packet can now be used by calling `to_bytes`
print(packet.to_bytes())

Warning

Even if the packet has the default configuration, is is necesary to craft it before sending it, otherwise it will raise a ValueError. The method is_crafted returns True if the packet is ready to be sent.