GW12 Network

GW12 Network Details

The GW12 Probes will wither use CC1120 at 173MHz or use the RPM Radios from Radiometrix. 151MHz modules with 100mW power output are used to ensure high power through ice transmissions.

RPM Radio Driver

The RPM Radio requires a form of handshaking/communication control between the radio module and the MCU so that no data is lost between the probe and radio module ([See manual]). The driver should not push more than ~4kbit/s average or it will fill its buffers.

The driver should also ensure that during a transmission sequence, it enters a low-power mode while waiting for other nodes to finish their transmission sequence.

STANDBY with Wake/DTR pin - if we do hopping, some radios could be put into standby (faster startup than poweroff).

SIGNAL - pin10 says "preamble detected" - so we should not try transmitting if its set (need to Scope and record its behavour)

CTS - may be simplest way to not over-fill radio rather than driver techniques? it hoes high when buffer is 66% full and low again once its < 33% full. Buffer is 96 bytes.

GW12 Star Network

The star network to be used with the GW12 Nodes requires several features to ensure the sensing tasks are fulfilled. These include:

• Network discovery
• Time synchronisation

GW12 Hopping Network

• Routing table
• Ping nodes
• Network discovery

a simple hopping network was implemented - with no auto-route discovery. We built in a simple routing table in each node which can be setup by the base station - and make sure we can cope with longer latencies etc (RPM will probably add > 20ms to forward a packet).

The route table also specifies the port to route to - so nodes can route from serial to radio, etc. Where the channels are numbered as follows:

NO_ROUTE        0
RS485           1
RADIO_868       2
RADIO_173       3
USB             4
RADIO_151       5
RADIO_RPM       5

probes have a default route table (once you run "deploy" on them). Wired probes need to route radio-serial for all packets not destined for them. The ID of probes should only be 30-39 as that has been defined for this deployment.

Routing:

routeget ID - prints the route table of a node

routeadd ID routeforID Channel - sets a route on node ID to route packets to Channel (eg 5 for RPM radio)

ping ID - pings a node - used for checking it is awake

GW12 Data/Instruction Packets

Should the communication between the devices include data and instruction/command packets? Should there be only one kind of packet or multiple different types?

I think there should be two kinds of packets: Short fixed-length command packets and longer data-packets.

Packet Structure

Packets are thus of size between 12 bytes for command packets and 8 to 264 bytes (256+8) for data packets.

Command Packet

* 8-bits PACKET_START_CHAR
* 8-bits PACKET_CHECK_CHAR
* 8-bits SOURCE_ID
* 8-bits DESTINATION_ID
* 1-bit COMMAND_ID
* 7-bits COMMAND
* 5-bytes data
* 16-bits CRC

Data Packet

* 8-bits PACKET_START_CHAR
* 8-bits PACKET_CHECK_CHAR
* 8-bits SOURCE_ID
* 8-bits DESTINATION_ID
* 1-bit DATA_ID
* 7-bits DATA_PKT_NUMBER
* 8-bits DATA_LENGTH
* PAYLOAD
* 16-bits CRC

Command Packet Types

Node Level

• Time synchronisation/Set Time
• Device identification
• Change sampling rates
• Change wake-up times
• Request sample
• Set LEDs/ID/Debug Parameter
• List files on uSD - could be tricky as its a long list
• Send file (or send new files?)

Network Level

• GW12 network commands / first draft of ideas