BLE Architecture#

The SiWx917 Network Processor (NWP) provides a Bluetooth Low Energy (BLE) implementation through the WiSeConnect SDK. The BLE stack is Bluetooth 5.4-compliant and supports multiple concurrent roles.

Note: As of January 2026, WiSeConnect SDK version 4.0 is the current version. This guide references APIs and features available in WiSeConnect SDK 4.0 and later versions.

BLE Stack Architecture#

The BLE stack runs on the NWP and provides a complete implementation of the Bluetooth Low Energy protocol. Applications interact with the BLE stack through the WiSeConnect SDK APIs, which abstract the underlying protocol details and provide a high-level interface for BLE operations.

The same NWP additionally runs the Wi-Fi MAC/LMAC and shares a single 2.4 GHz radio with BLE.

Key Characteristics:

• Bluetooth 5.4 Compliant: Full support for BLE 5.x features including extended advertising, periodic advertising, and enhanced connection procedures

• Multiple Concurrent Roles: Support for simultaneous operation in multiple BLE roles (Central, Peripheral, Broadcaster, Observer)

• Multiple Connections: Capability to maintain multiple simultaneous BLE connections

• GATT and GAP Support: Complete implementation of Generic Attribute Profile (GATT) and Generic Access Profile (GAP)

• Legacy Advertising: Support for legacy (non-extended) advertising for compatibility with BLE 4.x and simple use cases

• Extended Advertising and Initiating: Support for extended advertising (AE Advertiser) and extended connection initiation (AE Initiator) for BLE 5.0+ devices

• Security Manager Protocol (SMP): Support for pairing, bonding, and key distribution

Supported BLE Roles#

The SiWx917 NWP supports all four BLE roles defined in the Bluetooth specification:

1. Peripheral Role: Advertises its presence and accepts connections from central devices (phones, tablets, gateways).

• Common use cases: IoT sensors, wearables, beacons that need to be controlled

• Ideal for: Devices that provide services to mobile applications or other central devices

• See Peripheral role for implementation details

2. Central Role: Scans for advertising devices and initiates connections. Can maintain multiple simultaneous connections to peripheral devices.

• Common use cases: Gateways collecting data from multiple sensors, remote controls

• Ideal for: Devices that need to discover and connect to multiple peripherals

• See Central role for implementation details

3. Broadcaster Role: Transmits advertising data without accepting connections.

• Common use cases: Beacons, location tags, proximity detection

• Ideal for: One-way data transmission applications

• See Broadcaster role for implementation details

4. Observer Role: Receives advertising data without establishing connections.

• Common use cases: Beacon scanners, presence detection systems

• Ideal for: Scanning applications that don't require connections

• See Observer role for implementation details

The stack supports dual-role operation, allowing a device to operate as both Central and Peripheral simultaneously, enabling peer-to-peer communication scenarios.

Operating Mode Considerations#

The BLE stack behavior depends on the SiWx917 operating mode:

• NCP Mode (Network Co-Processor): The full BLE stack runs on the NWP. All BLE operations are handled by the NWP firmware, and the host (external MCU) communicates through SPI/SDIO/UART interfaces.

• RCP Mode (Radio Co-Processor): Only the BLE Controller runs on the NWP. The BLE Host stack runs on the external host processor (MPU). This mode provides more control over the host stack implementation.

• SoC/ACP Mode (Dual Core): The full BLE stack runs on the NWP, and the M4 Application Processor communicates with the NWP through the AHB interface and shared memory.

See: Mode-Specific Considerations for detailed differences.

BLE Version and Features#

The SiWx917 NWP implements a Bluetooth 5.4-compliant BLE stack through the WiSeConnect SDK. This provides comprehensive support for BLE 5.x features and backward compatibility with earlier BLE versions.

Supported BLE Features#

Core BLE Capabilities:

• BLE 5.4 Compliance: Full support for the latest Bluetooth Low Energy specification

• Multiple Concurrent Roles: Support for simultaneous operation as Central, Peripheral, Broadcaster, and Observer

• Dual Role Support: Can operate as both Central and Peripheral simultaneously

• Multiple Simultaneous Connections: Capability to maintain multiple BLE connections concurrently

BLE 5.x Advanced Features:

• Extended Advertising: Up to 200 bytes per advertising set (Extended advertising)

• Periodic Advertising: Uses the extended advertising data limits (Extended advertising)

• Extended Scanning: Support for extended scanning procedures (AE Scanner) for receiving extended advertising (see Extended advertising)

• Extended Initiating: Support for extended connection initiation procedures (AE Initiator) (see Central role)

• 2M PHY: High-speed 2 Mbps physical layer for increased throughput

• LE Coded PHY: Long-range PHY options (125 kbps and 500 kbps) for extended range applications

• Data Length Extension (DLE): Support for larger link-layer payloads up to 251 bytes (including L2CAP/ATT headers; see Data length extension)

• LE Secure Connections: Enhanced security with Elliptic Curve Diffie-Hellman (ECDH) key exchange

• LE Privacy 1.2: Support for resolvable private addresses (RPA) and address resolution (LE Privacy)

GATT and GAP Support:

• Generic Attribute Profile (GATT): Full GATT client and server implementation

• Generic Access Profile (GAP): Complete GAP implementation for device discovery and connection management

• UUID support: 16-bit Bluetooth SIG UUIDs, 32-bit custom UUIDs, and 128-bit UUIDs (including custom services and characteristics)

• All GATT-based Profiles: Support for all standard and custom GATT-based profiles and services

Security Features:

• Pairing Methods: Just Works, Numeric Comparison, and Passkey Entry are supported; Out-of-Band pairing is not supported (see Pairing and bonding)

• Bonding: Secure storage of long-term keys for persistent connections

• Encryption: AES-128 encryption for data protection

API documentation: See Developing with WiSeConnect SDK and the in-guide BLE API reference.

PHY Options#

The SiWx917 supports multiple BLE physical layer (PHY) options, allowing applications to optimize for throughput, range, or power consumption.

Supported PHY Types#

1M PHY (Default)

• Symbol Rate: 1 Mbps

• Use Case: Standard BLE communication, maximum compatibility

• Range: Standard BLE range (~10-30 meters depending on environment)

• Throughput: Typical application throughput up to ~700 kbps (measured values vary with configuration—for example, NCP vs CCP, connection interval, host interface)

• API: Default PHY for all connections unless explicitly changed

2M PHY (BLE 5.0+)

• Symbol Rate: 2 Mbps

• Use Case: High-throughput applications requiring faster data transfer

• Range: Similar to 1M PHY

• Throughput: Typical application throughput up to ~1.3 Mbps (measured values vary with configuration—for example, NCP vs CCP, connection interval, host interface)

• API: Use rsi_ble_setphy() to request 2M PHY on a connection

Note: Both devices must support 2M PHY for it to be used

LE Coded PHY - 500 kbps (BLE 5.0+)

• Symbol Rate: 500 kbps (S=2 coding)

• Use Case: Extended range applications with moderate data requirements

• Range: Approximately 1.5-2x the range of 1M PHY with 4-6 dB improved sensitivity

• Throughput: Lower than 1M PHY due to coding overhead

• API: Use rsi_ble_setphy() to request Coded PHY (500 kbps)

LE Coded PHY - 125 kbps (BLE 5.0+)

• Symbol Rate: 125 kbps (S=8 coding)

• Use Case: Maximum range applications with low data rate requirements

• Range: Maximum BLE range with best sensitivity

• Throughput: Lowest throughput due to highest coding overhead

• API: Use rsi_ble_setphy() to request Coded PHY (125 kbps)

For PHY selection, negotiation, and APIs after connection, see BLE initialization and configuration.

Maximum Simultaneous Connections#

The SiWx917 NWP supports multiple simultaneous BLE connections, enabling applications to communicate with multiple devices concurrently.

Full treatment—role distribution, connection management, memory considerations, and APIs—is in Maximum simultaneous connections.

Advertising Set Limits#

BLE 5.0 advertising sets allow multiple independent advertising configurations. On SiWx917, the number of extended advertising (AE) sets is configurable at build time but capped at 2; legacy advertising uses a single instance path.

For advertising set capabilities, legacy vs extended advertising, build configuration, and APIs, see Advertising set limits and Extended advertising.

• Power Management Developer Guide: BLE power save modes and optimization strategies

APIs Used in This Section#

Integration:

• PHY negotiation, stack initialization, callback registration, and full API tables for connection limits and advertising sets are in BLE initialization and configuration

• Aggregated API grouping: BLE API reference

• SDK entry: Developing with WiSeConnect SDK