Lynx Modules

What is a Lynx Module?

A Lynx Module represents a REV Control Hub or REV Expansion Hub in your robot code. Every hub connected to your robot has a corresponding LynxModule object that allows you to configure hub-wide settings and access hardware information.

The most important feature of the LynxModule API is bulk reading, which can significantly improve your robot's loop time.

Initializing Lynx Modules

It's a good idea to initialize your Lynx Modules before initializing the rest of your hardware.

List<LynxModule> allHubs = hardwareMap.getAll(LynxModule.class);

You'll use this list throughout the rest of the page.

What are Bulk Reads?

Normally, every time your program reads a motor encoder or digital sensor, the Control Hub must communicate with the hardware.

For example:

int left = leftMotor.getCurrentPosition();
int right = rightMotor.getCurrentPosition();

Without bulk reads, each call requires its own communication with the hub.

A bulk read requests all non-I2C sensor data from a hub at once. Once the data is cached, subsequent reads use the cached values instead of sending additional commands.

Because a bulk read takes about the same amount of time as a single hardware read, reading multiple sensors becomes much faster.

[!NOTE] Bulk reads only apply to hardware connected to the same hub and do not include I2C devices such as color sensors or distance sensors.

Bulk Caching Modes

The FTC SDK provides three bulk caching modes.

For most teams, AUTO is the best choice.

OFF Mode

OFF mode disables bulk caching entirely.

for (LynxModule hub : allHubs) {
    hub.setBulkCachingMode(LynxModule.BulkCachingMode.OFF);
}

[!WARNING] We do not recommend using OFF mode. Without bulk reads, every hardware read requires a separate communication with the hub, resulting in slower loop times.

AUTO Mode

AUTO mode is the easiest and safest way to use bulk reads.

for (LynxModule hub : allHubs) {
    hub.setBulkCachingMode(LynxModule.BulkCachingMode.AUTO);
}

During each loop, the first hardware read performs a bulk read. Additional reads from the cache are fast.

while (opModeIsActive()) {

    int left = leftMotor.getCurrentPosition();
    int right = rightMotor.getCurrentPosition();
    int front = frontEncoder.getCurrentPosition();

}

A Small Drawback

If you read the same hardware value twice, AUTO mode performs another bulk read.

int left1 = leftMotor.getCurrentPosition();
int left2 = leftMotor.getCurrentPosition();

While this isn't ideal, AUTO mode is still recommended because it's simple and difficult to misuse.

MANUAL Mode

MANUAL mode gives you complete control over the bulk cache.

for (LynxModule hub : allHubs) {
    hub.setBulkCachingMode(LynxModule.BulkCachingMode.MANUAL);
}

At the start of every loop, clear the cache.

while (opModeIsActive()) {

    for (LynxModule hub : allHubs) {
        hub.clearBulkCache();
    }

    int left1 = leftMotor.getCurrentPosition();
    int left2 = leftMotor.getCurrentPosition();

}

Even though getCurrentPosition() is called twice, only one bulk read occurs because both values come from the same cached data.

[!WARNING] If you forget to clear the cache, your program will continue reading old sensor values. This can cause your robot to behave unpredictably.

Clearing the Cache Inside Other Loops

A common mistake is only clearing the cache in the main OpMode loop.

If you have additional while or for loops, you should clear the cache there as well.

while (timer.milliseconds() < 2000) {

    for (LynxModule hub : allHubs) {
        hub.clearBulkCache();
    }

    doSomething();
}

If doSomething() also contains loops, those loops should clear the cache as well.

Choosing Between AUTO and MANUAL

Unless you're optimizing every millisecond of your loop time, AUTO mode is the recommended choice.

Measuring Battery Voltage

The Lynx Module can report the input voltage supplied by your robot battery.

for (LynxModule hub : allHubs) {

    double voltage = hub.getInputVoltage(VoltageUnit.VOLTS);

}

Monitoring battery voltage can help with:

• Voltage compensation
• Battery health
• Driver telemetry
• Debugging robot performance

Measuring Current

You can also measure the total current draw of each hub.

for (LynxModule hub : allHubs) {

    double current = hub.getCurrent(CurrentUnit.AMPS);

}

Current monitoring is useful for:

• Detecting stalled motors
• Finding mechanical binding
• Monitoring power usage
• Debugging electrical problems

Best Practices

• Initialize your Lynx Modules before the rest of your hardware.
• Enable AUTO bulk caching unless you have a reason to use MANUAL.
• If using MANUAL mode, clear the cache at the start of every control loop.
• Remember that bulk reads do not include I2C devices.
• Monitor voltage and current through the Lynx Module for easier debugging.