Pre-Filter Tutorial - Zebra Technologies Techdocs

Overview

This Tutorial provides a walk-through of the steps to perform Pre-Filter configuration using RFID3 API

Create The Project

Start by creating a new project in Android Studio. For help, see the Android Studio tutorial.
Refer Hello RFID to prepare basic setup to work with RFID Reader and then follow this guide

Details

Pre-filters are the same as the Select command of C1G2 specification. Once applied, pre-filters are applied prior to Inventory and Access operations.

Singulation

Refer Singulation for details. In order to filter tags that match a specific condition, it is necessary to use the tag-sessions and their states (setting the tags to different states based on match criteria - reader.Actions.PreFilters.add) so that while performing inventory, tags can be instructed to participate (singulation - reader.Config.Antennas.setSingulationControl) or not participate in the inventory based on their states.

State-Aware Singulation

In state-aware singulation the application can specify detailed controls for singulation: Action and Target. Action indicates whether matching Tags assert or deassert SL (Selected Flag), or set their inventoried flag to A or to B. Tags conforming to the match criteria specified using the method reader.Actions.PreFilters.Add are considered matching and the remaining are non-matching. Target indicates whether to modify a tag’s SL flag or its inventoried flag, and in the case of inventoried it further specifies one of four sessions.

Setting it up

The following are the steps to use pre-filters

Add pre-filters
Set appropriate singulation controls
Perform Inventory or Access operation

Limitations for RE40 Integrated Mobile Computers

Pre-Filters will be applied only when profile is set to "USER_DEFINED". Refer profiles here.

Each RFID reader supports a maximum number of pre-filters per antenna as indicated by reader.ReaderCapabilites.getMaxNumPreFilters which can be known using the ReaderCapabilities. The application can set pre-filters using reader.Actions.PreFilters.add and remove using reader.Actions.PreFilters.delete.


// Add state aware pre-filter for given EPC or Tag ID
    private void addfilters(String tag) {
        // Add state aware pre-filter
        PreFilters filters = new PreFilters();
        PreFilters.PreFilter filter = filters.new PreFilter();
        filter.setAntennaID((short) 1);// Set this filter for Antenna ID 1
        filter.setTagPattern(tag);// Tags which starts with passed pattern
        filter.setTagPatternBitCount(tag.length() * 4);
        filter.setBitOffset(32); // skip PC bits (always it should be in bit length)
        filter.setMemoryBank(MEMORY_BANK.MEMORY_BANK_EPC);
        filter.setFilterAction(FILTER_ACTION.FILTER_ACTION_STATE_AWARE); // use state aware singulation
        filter.StateAwareAction.setTarget(TARGET.TARGET_INVENTORIED_STATE_S1); // inventoried flag of session S1 of matching tags to B
        filter.StateAwareAction.setStateAwareAction(STATE_AWARE_ACTION.STATE_AWARE_ACTION_INV_B_NOT_INV_A);
        // not to select tags that match the criteria
        try {
            reader.Actions.PreFilters.add(filter);
        } catch (InvalidUsageException e) {
            e.printStackTrace();
        } catch (OperationFailureException e) {
            e.printStackTrace();
        }
    }

Set singulation control

Now that the pre-filters are set (i.e., tags are classified into matching or non-matching criteria), the application needs to specify which tags should participate in the inventory using reader.Config.Antennas.setSingulationControl(). Singulation Control must be specified with respect to each antenna like pre-filters.


// Set the singulation control matching with prefilter
    private void setSingulationForFilter() {
        try {
            Antennas.SingulationControl s1_singulationControl = reader.Config.Antennas.getSingulationControl(1);
            s1_singulationControl.setSession(SESSION.SESSION_S1);
            s1_singulationControl.Action.setInventoryState(INVENTORY_STATE.INVENTORY_STATE_B);
            s1_singulationControl.Action.setPerformStateAwareSingulationAction(true);
            reader.Config.Antennas.setSingulationControl(1, s1_singulationControl);
        } catch (InvalidUsageException e) {
            e.printStackTrace();
        } catch (OperationFailureException e) {
            e.printStackTrace();
        }
    }

Performing operation

Inventory or Access operation when performed after setting pre-filters, use the tags filtered out of pre-filters for their operation.


try {
    reader.Actions.Inventory.perform();
    Thread.sleep(5000);
    reader.Actions.Inventory.stop();
} catch (InvalidUsageException e) {
    e.printStackTrace();
} catch (OperationFailureException e) {
    e.printStackTrace();
} catch (InterruptedException e) {
    e.printStackTrace();
}

Closer look

Pre-Filter i.e. select command moves matching tags to given state and then applying matching singulation results in interested tags getting inventoried
setStateAwareAction has various conditions set to matching and non matching group of tags
After pre-filter application tag moves its state if matching and then it participates in inventory irrespective to SESSION behaviour - given session is also matching

What's Next

Alter singulationControl.Action.setInventoryState(INVENTORY_STATE.INVENTORY_STATE_B) with INVENTORY_STATE.INVENTORY_STATE_A to select non matching tags

Pre-Filter Configurations Tutorial