This example is intended as an advance example to show how to use the RF Driver to implement a proprietary radio protocol. The example showcase a simple time-slotted synchronous collector and sensor protocol and is meant to be used together with the rfSensor example.
The collector can support a small network of sensors; each sensor will have to associate itself with the collector in order to join the network. If a sensor drop out of the network it will be marked as orphan and ignored until re-associating with the collector.
Board_GPIO_LED0- Heartbeat LED indicating the processingTask is running
If you're using an IDE (such as CCS or IAR), please refer to Board.html in your project directory for resources used and board-specific jumper settings. Otherwise, you can find Board.html in the directory <SDK_INSTALL_DIR>/source/ti/boards/<BOARD>.
Build and download the example to the development board. When running the example, a serial printout is available over UART, containing information on all sensors connected to the collector device. The following default parameters are used for the UART peripheral:
| UART Param | Default Values |
|---|---|
| Baud Rate | 115200 |
| Data Length | 8 bits |
| Parity | None |
| Stop Bits | 1 bit |
| Flow Control | None |
The radio protocol is setup to support N number of sensors in one network. The number of sensors supported depends on the size of the time-slot and the collector beacon interval. All communication between collector and sensor is confined within the beacon interval. At the beginning of each beacon interval the collector sends out a beacon to allow sensors to associate itself with the network. The remaining part of the time window given by the beacon interval time is used for communication with associated sensors.
Per default, the example uses a 2 s beacon interval and 200 ms time-slot size. The numbers of supported nodes (N) is calculated based on this number as such: (2000 / 200) - 1 = 9. The beacon interval and time-slot size can be adjusted by changing the pre-defined value of BEACON_INTERVAL and TIMESLOT_SIZE respectively. For cases where a low data rate PHY is used, for example SimpleLink Long Range, it might be necessary to increase the TIMESLOT_SIZE.
A graphical representation of how the beacon interval is divided is shown below:
The first time-slot is reserved for the collector beacon. A sensor that listens for a beacon may respond to a beacon, requesting association with the collector. The sequence diagram below shows the communication exchange between a collector and sensor during an association.
The sensor side application implements a light weight collision avoidance functionality used during association. This include "Listen before talk" combined with a random start delay calculated during initialization.
During association, the collector will distribute a time-slot to the sensor. The sensor will then use the time stamp provided by the Radio Core together with the provided time-slot to schedule its report interval.
During a sensor time-slot, the collector will listen for data from the sensor assigned to that particular time slot. When receiving a sensor packet, the collector will acknowledge the sensor by responding with an ACK. A sequence diagram of the complete beacon interval is seen below:
When expecting to receive a packet from a particular sensor, the address filtering feature provided by the Radio Core is leveraged.
The collector expects each sensor to be given a unique device address and the behavior if multiple sensors have the same address is undefined.
There is still a possibility to receive "false" packets if the address field happens to match. However, for a packet to be valid, the header also needs to match what is expected by the application.
There is no drift compensation between the collector and sensor; over time the collector and sensor will drift apart and lose the connection. The connection will be re-established when both the collector and sensor consider the sensor an orphan. A simple way of implementing drift compensation is to leverage the Radio Core timestamp feature on both the collector and sensor and to report the deviation to the sensor during each acknowledgment so that it can re-align.