How does slave latency save power?

Without slave latency, the peripheral must wake and respond at every connection event. With latency=N, the peripheral can sleep through N events, waking only when it has data or after N skips. Effective sleep = CI * (1+N). With CI=30 ms and latency=9: sleep up to 300 ms between responses, reducing wake-ups by 10x.

What are the constraints?

Maximum value: 499 events. Must satisfy: (1 + slave_latency) * CI < supervision_timeout. The peripheral must respond at least once per supervision timeout to keep the connection alive. If it skips too many events and misses the timeout, the connection drops.

Does the central also benefit?

The central still transmits at every connection event (it does not know which events the peripheral will skip). Central power savings come from shorter CI, not from slave latency. Slave latency primarily benefits the peripheral's power budget.

Wireless Protocols

BLE Slave Latency

Q: Does the central also benefit?

The central still transmits at every connection event (it does not know which events the peripheral will skip). Central power savings come from shorter CI, not from slave latency. Slave latency primarily benefits the peripheral's power budget.

BLE Slave Latency allows a peripheral to skip up to 499 consecutive connection events without responding, effectively multiplying its sleep time by (1 + latency) while maintaining the connection. The peripheral must respond before the supervision timeout expires. This decouples the peripheral's wake rate from the connection interval, enabling low power for the peripheral while the central maintains fast response capability.

Category: Wireless Protocols

Range: 0-499 events

Understanding Slave Latency

With slave latency = 0, the peripheral wakes at every CI. With latency = N, the peripheral can sleep through N events. When the peripheral has data to send (e.g., a button press), it wakes at the next event, achieving response time = CI. Without data, it sleeps up to N×CI between wake-ups.

This is powerful: CI=15 ms with latency=19 gives fast 15 ms response when needed, but the peripheral sleeps up to 300 ms when idle, equivalent to a 300 ms CI in power terms but with 15 ms latency capability.

Slave Latency Parameters

Effective sleep interval:
T_sleep = CI × (1 + slave_latency)

Constraint:
(1 + SL) × CI < supervision_timeout

Example: CI=15 ms, SL=19:
T_sleep = 15 × 20 = 300 ms max
Response time = 15 ms (next event)

Slave Latency Scenarios

CI	Slave Latency	Max Sleep	Response	Use Case
7.5 ms	0	7.5 ms	7.5 ms	Gaming
15 ms	19	300 ms	15 ms	Keyboard
30 ms	9	300 ms	30 ms	Wearable
100 ms	4	500 ms	100 ms	Sensor

Common Questions

Frequently Asked Questions

How does it save power?

Peripheral sleeps N events, waking only with data or after N skips. CI=30 ms, latency=9: sleep 300 ms, 10× fewer wake-ups.

Constraints?

Max 499. Must satisfy: (1+SL)×CI < supervision_timeout. Missing timeout drops the connection.

Central benefit?

Central still transmits every event (doesn't know which the peripheral skips). Slave latency benefits only the peripheral.

Related Terms

← BLE Range Supervision Timeout →

BLE Optimization

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