rfEasyLink_listenBeforeTalk Example

Example Summary

This example includes the EasyLink API and uses it to configure the RF driver to assess the communication channel before transmitting any packets, i.e. Listen Before Talk (LBT); the radio will first enter RX mode to assess the channel, if it is idle (RSSI below a set threshold) it proceeds to transmit a packet. If the channel is busy (RSSI above the set threshold) the radio will back off for a random period before assessing the channel again; it will do this a certain number of times before failing altogether.

This project can be run in conjunction with the rfEasyLinkRx project; a third board, managed by SmartRF Studio, emitting a continuous carrier wave may be used as a jammer to simulate high load networks.

For more information on the EasyLink API and usage refer to https://processors.wiki.ti.com/index.php/SimpleLink-EasyLink

Peripherals Exercised

Board_PIN_LED1 - Indicates that a packet has been transmitted
Board_PIN_LED2 - Indicates that the CCA algorithm had failed to detect an idle channel during which to transmit a given packet Board_PIN_LED1 & Board_PIN_LED2 indicate an error

Resources & Jumper Settings

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>.

Example Usage

The example code can be tested with a receiver managed by SmartRF Studio, or one board running the rfEasyLinkRx example as the receiver, and another board connected to SmartRF Studio, acting as a jammer at 868.0 MHz (433.92 MHz for the CC1350-LAUNCHXL-433 board).

The transmitter will attempt to transmit a packet every 100 ms. Board_PIN_LED1 will toggle each time a packet is successfully transmitted. Board_PIN_LED2 will toggle if the Clear Channel Assessment (CCA) fails and the packet is not transmitted. If the macro RFEASYLINKLBT_RETRANSMIT_PACKETS is set to 1 the application will attempt to retransmit any failed packets indefinitely; if set to 0 it will skip the failed packet and move on to the next packet in sequence. This cycle will continue.

Before running this application you should first start the rfEasyLinkRx on a second board to see that the transmitted packets are received.

Application Design Details

This example shows how to use the EasyLink API to access the RF driver, set the frequency, assess the channel and transmit packets. The TX API used is asynchronous (non-blocking).

The rfEasyLinkListenBeforeTalk example will transmit a packet every 100 ms if the channel is idle. The TX API used will run a Clear Channel Assessment (CCA) algorithm to determine if the channel is idle, it does this by comparing the channel RSSI against a set threshold, if it is lower than the threshold the channel is considered to be idle, else it is busy. If the channel is busy the radio will back off for a certain time period before reassessing the channel, it does this a certain number of times before giving up and declaring a “channel busy” failure. Board_PIN_LED2 will indicate when this condition occurs. For every successful transmission Board_PIN_LED1 will be toggled. An error has occured if both Board_PIN_LED1 and Board_PIN_LED2 are toggled.

A single task, “rfEasyLinkLbtFnx”, configures the RF driver through the EasyLink API and transmits messages.

EasyLink API

Overview

The EasyLink API should be used in application code. The EasyLink API is intended to abstract the RF Driver in order to give a simple API for customers to use as is or extend to suit their application[Use Cases] (@ref USE_CASES).

General Behavior

Before using the EasyLink API:

The EasyLink Layer is initialized by calling EasyLink_init(). This initializes and opens the RF driver and configures a modulation scheme passed to EasyLink_init.
The RX and TX can operate independently of each other.

The following is true for receive operation:

RX is enabled by calling EasyLink_receive() or EasyLink_receiveAsync()
Entering RX can be immediate or scheduled
EasyLink_receive() is blocking and EasyLink_receiveAsync() is non-blocking
The EasyLink API does not queue messages so calling another API function while in EasyLink_receiveAsync() will return EasyLink_Status_Busy_Error
An Async operation can be cancelled with EasyLink_abort()

The following apply for transmit operation:

TX is enabled by calling EasyLink_transmit(), EasyLink_transmitAsync() or EasyLink_transmitCCAAsync()
TX can be immediate or scheduled
EasyLink_transmit() is blocking and EasyLink_transmitAsync(), EasyLink_transmitCCAAsync() are non-blocking
EasyLink_transmit() for a scheduled command, or if TX cannot start
The EasyLink API does not queue messages so calling another API function while in either EasyLink_transmitAsync() or EasyLink_transmitCCAAsync() will return EasyLink_Status_Busy_Error
An Async operation can be cancelled with EasyLink_abort()

Error Handling

The EasyLink API will return EasyLink_Status containing success or error code. The EasyLink_Status codes are:

EasyLink_Status_Success
EasyLink_Status_Config_Error
EasyLink_Status_Param_Error
EasyLink_Status_Mem_Error
EasyLink_Status_Cmd_Error
EasyLink_Status_Tx_Error
EasyLink_Status_Rx_Error
EasyLink_Status_Rx_Timeout
EasyLink_Status_Busy_Error
EasyLink_Status_Aborted

Power Management

The power management framework will try to put the device into the most power efficient mode whenever possible. Please see the technical reference manual for further details on each power mode.

The EasyLink Layer uses the power management offered by the RF driver Refer to the RF Driver documentation for more details.

Supported Functions

| Generic API function          | Description                                        |
|-------------------------------|----------------------------------------------------|
| EasyLink_init()               | Init's and opens the RF driver and configures the  |
|                               | specified modulation                               |
| EasyLink_transmit()           | Blocking Transmit                                  |
| EasyLink_transmitAsync()      | Non-blocking Transmit                              |
| EasyLink_transmitCCAAsync()   | Non-blocking Transmit with Clear Channel Assessment|
| EasyLink_receive()            | Blocking Receive                                   |
| EasyLink_receiveAsync()       | Non-blocking Receive                               |
| EasyLink_abort()              | Aborts a non-blocking call                         |
| EasyLink_EnableRxAddrFilter() | Enables/Disables RX filtering on the Addr          |
| EasyLink_GetIeeeAddr()        | Gets the IEEE Address                              |
| EasyLink_SetFreq()            | Sets the frequency                                 |
| EasyLink_GetFreq()            | Gets the frequency                                 |
| EasyLink_SetRfPwr()           | Sets the TX Power                                  |
| EasyLink_GetRfPwr()           | Gets the TX Power                                  |

Frame Structure

The EasyLink implements a basic header for transmitting and receiving data. This header supports addressing for a star or point-to-point network with acknowledgements.

Packet structure:

 _________________________________________________________
|           |                   |                         |
| 1B Length | 1-64b Dst Address |         Payload         |
|___________|___________________|_________________________|

Note for IAR users: When using the CC1310DK, the TI XDS110v3 USB Emulator must be selected. For the CC1310_LAUNCHXL, select TI XDS110 Emulator. In both cases, select the cJTAG interface.