emMQTT

SEGGER emMQTT is a compact MQTT client implementation built for embedded IoT devices where memory and power budgets are tight. Implementing the MQTT 3.1.1 specification, emMQTT provides full publish/subscribe messaging with all three Quality of Service levels, QoS 0 (at most once), QoS 1 (at least once), and QoS 2 (exactly once), enabling developers to choose the right delivery guarantee for each message type. At approximately 2.4 KB of ROM on a Cortex-M4 target and just 84 bytes of RAM per client context, emMQTT adds negligible overhead to even the most constrained sensor nodes and edge devices.

Security and Broker Compatibility

emMQTT supports SSL/TLS encryption and client certificate authentication when used with SEGGER emSSL, securing MQTT traffic end-to-end without requiring a separate security layer. The client supports will messages for graceful handling of unexpected disconnections and the retain flag for persistent message delivery. It has been tested with popular brokers including Mosquitto, HiveMQ, and AWS IoT Message Broker, ensuring interoperability across cloud and on-premise MQTT infrastructure.

Core Capabilities

• Full publish/subscribe client: topic filtering, subscription management, and QoS-aware message delivery
• Persistent sessions: clients can reconnect and resume subscriptions without re-establishing state from scratch
• Small, predictable memory footprint: around 2.4 KB ROM and 84 bytes RAM per client context on Cortex-M4, so an MQTT client fits alongside sensor and control code on the same microcontroller
• Callback-driven API: application code registers handlers for connection state, incoming messages, and publish acknowledgements rather than polling
• Interoperability testing: verified against Mosquitto, HiveMQ, and AWS IoT Message Broker for both on-premise and cloud deployments

TCP/IP Stack Independence

emMQTT is independent of the underlying TCP/IP stack, any stack providing a socket interface can be used through a simple callback API. It is optimised for SEGGER emNet but works equally well with third-party stacks, giving teams flexibility to integrate emMQTT into existing network architectures. This stack independence matters for Indian IoT integrators retrofitting connectivity onto boards that already run a vendor-supplied networking stack, since emMQTT does not force a wholesale replacement of the existing TCP/IP layer.

SEGGER Ecosystem Integration

Paired with emSSL, emMQTT delivers TLS-secured telemetry without a separate security stack integration, and paired with emNet, it gains a matched, memory-efficient IPv4/IPv6 foundation built by the same vendor. Because emMQTT, emSSL, and emNet share one royalty-free, one-time-payment licensing model, IoT product teams can budget connectivity, security, and messaging middleware as a single fixed line item rather than negotiating separate runtime royalties for each layer. The royalty-free, one-time-payment licensing model makes it straightforward to deploy across high-volume IoT product lines without per-unit cost concerns.