BLE5 Channel Assessment Command Handler

Introduction

The purpose of the Channel Assessment command handler is to assess the noise level of a BLE channel. The return status status will indicate if the BLE channel is busy or idle, with reference to a specified threshold.

Usage

1. RCL has been initialized (See RCL_init) and a handle must exist (See RCL_open).
2. The RCL_CMD_BLE5_CH_ASSESSMENT_t command has been initialized and configured.

Once these steps have been completed, RCL_Command_submit is called to start the command. Once submitted, the caller can either use RCL_Command_pend or a callback to wait for the command's conclusion and proceed with any additional tasks such as post-processing or the submitting of new commands.

The stop time needs to be longer than the assessmentDuration parameter. Otherwise, the command will be stopped before measurement has been completed. Also the assessmentDuration should not be lower than 8 (2us). This will result in RCL_CommandStatus_Error_Param.

Since this command is very simple, it doesn't use a context struct or a stats struct like other BLE commands. The following code snippet shows a normal use-case for the command.

void runChannelAssessment(void)
{
    RCL_init();
    RCL_Handle h = RCL_open(&rclClient, &LRF_configBle);

    /* Setup channel assessment command */
    chAssessmentCmd = RCL_CmdBle5ChAssessment_DefaultRuntime();
    chAssessmentCmd.channel = 37;
    chAssessmentCmd.assessmentThreshold = -70;
    chAssessmentCmd.assessmentDuration = RCL_SCHEDULER_SYSTIM_US(100);

    chAssessmentCmd.common.phyFeatures = PHY_FEATURES;
    chAssessmentCmd.common.scheduling = RCL_Schedule_Now;
    chAssessmentCmd.common.runtime.callback = chAssessmentCallback;
    chAssessmentCmd.common.runtime.lrfCallbackMask.value = 0;
    chAssessmentCmd.common.runtime.rclCallbackMask.value = RCL_EventLastCmdDone.value;
    chAssessmentCmd.common.timing.relGracefulStopTime = RCL_SCHEDULER_SYSTIM_US(450);

    /* Submit command and wait for it to conclude */
    RCL_Command_submit(h, &chAssessmentCmd);
    RCL_Command_pend(&chAssessmentCmd);

    if (chAssessmentCmd.common.status == RCL_CommandStatus_ChannelBusy)
    {
        // Do something
    }
    else if (chAssessmentCmd.common.status == RCL_CommandStatus_ChannelIdle)
    {
        // Do something
    }
    else
    {
        // Error handling
    }

    RCL_close(h);
}

Architecture

This command handler is based on the BLE5 Generic Rx Command Handler. However, it is simpler in design and will only open an Rx window for RSSI measurements the possibility of receiving any packets. The Rx window is open during the time specified by the assessmentDuration parameter. During this time, a sample is collected every 5us. The averaged result of all samples within the Rx window is then compared to the assessmentThreshold parameter. The comparison will yield either RCL_CommandStatus_ChannelBusy or RCL_CommandStatus_ChannelIdle as the commend status, when the averaged result is respectively above or below the configured assessmentThreshold parameter. If 0 samples have been collected at this point, RCL_CommandStatus_Error_Param will be given instead. The Rx window is then closed.

The following activity diagram illustrates the behavior of the channel assessment command handler.

BLE Channel Assessment handler state machine

Events

The following tables list the events handled.

RCL Event (In)	Description
RCL_EventSetup	Setup has been performed
RCL_EventTimerStart	Timer-based start signalled

RCL Event (Out)	Description
RCL_EventCmdStarted	Command handler has accepted and started executing
RCL_EventLastCmdDone	The RCL is finished with the command

LRF Event	Description
LRF_EventOpDone	The PBE operation has finished
LRF_EventOpError	The PBE operation has finished with error or hard stop
LRF_EventRfesoft0	The RFE confirms the first RSSI measurement can be read