Supported Targets	ESP32	ESP32-C2	ESP32-C3	ESP32-C5	ESP32-C6	ESP32-C61	ESP32-H2	ESP32-S3

ESP-IDF BLE ACL Latency Test - Peripheral

This example demonstrates how to measure BLE ACL (Asynchronous Connection-Less) link latency. The peripheral acts as a GATT server that echoes back any data written to it, allowing the central device to measure round-trip time (RTT) and calculate one-way latency.

This demo should be used together with the cent (central) example.

How It Works

The peripheral advertises with the device name ESP_ACL_LATENCY
When a central device connects, the peripheral accepts the connection
The peripheral provides a GATT service with a characteristic that supports both write and notify
When data is written to the characteristic, the peripheral immediately echoes it back via notification
The central measures the time between sending and receiving to calculate RTT and latency

Test Flow Diagram

    ┌──────────────┐                              ┌──────────────┐
    │   Central    │                              │  Peripheral  │
    │ (GATT Client)│                              │ (GATT Server)│
    └──────┬───────┘                              └──────┬───────┘
           │                                             │
           │                                             │  Advertising
           │                                             │  "ESP_ACL_LATENCY"
           │  Scan & Connect                             │
           │ ─────────────────────────────────────────>  │
           │                                             │
           │  Connection Established                     │
           │ <─────────────────────────────────────────> │
           │                                             │
           │  MTU Exchange, Service Discovery            │
           │ <─────────────────────────────────────────> │
           │                                             │
           │  ──────────── Latency Test ─────────────    │
           │                                             │
           │  Write [SEQ=N, 242 bytes]                   │
           │ ─────────────────────────────────────────>  │
           │                                     ┌───────┴───────┐
           │                                     │ Echo the same │
           │                                     │ data back via │
           │                                     │ Notification  │
           │                                     └───────┬───────┘
           │  Notification [SEQ=N, 242 bytes]            │
           │ <─────────────────────────────────────────  │
           │                                             │
           │  ... Repeat for 100 packets ...             │
           │                                             │
    ┌──────┴───────┐                              ┌──────┴───────┐
    │   Central    │                              │  Peripheral  │
    └──────────────┘                              └──────────────┘

                    ┌─────────────────────────────────┐
                    │     Latency Calculation         │
                    ├─────────────────────────────────┤
                    │  RTT = recv_time - send_time    │
                    │  One-way Latency = RTT / 2      │
                    │  Typical Result: 6-10 ms        │
                    └─────────────────────────────────┘

How to Use Example

Hardware Required

Two development boards with supported SoC (e.g., ESP32-C3-DevKitC, ESP32-DevKitC, etc.)
Two USB cables for power supply and programming

See Development Boards for more information.

Configure the Project

Before project configuration and build, be sure to set the correct chip target using:

bash

idf.py set-target <chip_name>

Build and Flash

Build the project and flash it to the board:

bash

idf.py -p PORT flash

(Replace PORT with the serial port name, e.g., /dev/ttyUSB0 on Linux or COM3 on Windows)

Monitor

Run idf.py -p PORT monitor to view the serial output.

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example Output

I (362) BLE_ACL_LATENCY_PERIPH: BLE ACL Latency Test - Peripheral
I (372) phy_init: phy_version 310,dde1ba9,Jun  4 2024,16:38:11
I (432) BLE_ACL_LATENCY_PERIPH: GATT server register, status=0, app_id=0
I (442) BLE_ACL_LATENCY_PERIPH: Create attribute table successfully, the number handle=4
I (442) BLE_ACL_LATENCY_PERIPH: SERVICE_START_EVT, status=0, service_handle=40
I (452) BLE_ACL_LATENCY_PERIPH: Advertising started
I (462) BLE_ACL_LATENCY_PERIPH: Peripheral ready, waiting for connection...
I (5532) BLE_ACL_LATENCY_PERIPH: ESP_GATTS_CONNECT_EVT, conn_id=0, remote 7c:df:a1:66:a6:00
I (5892) BLE_ACL_LATENCY_PERIPH: MTU exchange, MTU=517
I (5912) BLE_ACL_LATENCY_PERIPH: Connection params updated: status=0, conn_int=6, latency=0, timeout=500

GATT Service Structure

Attribute	UUID	Properties	Description
Service	0x1234	-	Latency test service
Char	0x5678	Write, Notify	Write data, receive echo back
CCCD	0x2902	Read, Write	Client Characteristic Config

Troubleshooting

For any technical queries, please open an issue on GitHub. We will get back to you soon.