> ## Documentation Index
> Fetch the complete documentation index at: https://dragonwingdocs.qualcomm.com/llms.txt
> Use this file to discover all available pages before exploring further.

# QMI Overview

> QMI client and service messaging, TLV encoding, transactions, and transport.

Qualcomm MSM Interface (QMI) is a messaging format and interface model for communication between software components running on different processors or subsystems. QMI defines the message semantics; it does not manage hardware resources. A transport such as QRTR carries the encoded message.

## Client and service model

QMI uses a client/service model. A client can communicate with multiple services, and a service can serve multiple clients. Communication has two forms:

* **Request and response** – A client sends an operation request and matches the response to that request.
* **Indication** – A service sends an unsolicited event after a client registers to receive a class of events.

## QMI message format

A QMI message has a small header followed by a series of typed fields. Each field is identified by a type tag, so the receiver knows what data to expect. This format lets the same message structure be used for requests, responses, and indications without requiring separate hand-written encoders for each one.

## Marshaling and transport separation

The encode/decode library converts between the C structures your code uses and the QMI wire format. The interface library manages QMI handles, service connections, callbacks, and message transport. Keeping these responsibilities separate lets a driver describe its data once and use the same codec for requests, responses, and indications.

## Concurrency and latency

The codec does not access global shared state and can be used without codec-level locking. The interface library protects shared resources with mutexes. QMI messages should remain short enough for the latency requirements of the client; large or slow operations should be designed with explicit asynchronous completion rather than holding a synchronous request open indefinitely.

## Next steps

* [Client API](client-api) — Create clients, connect to services, and send requests
* [Service API](service-api) — Register services and handle client requests
* [Examples](examples) — See how request/response and indication exchanges work