ezsp 10.0.0

Ember ZNet Serial Protocol
Documentation

ezsp

Rust implementation of the EmberZNet Serial Protocol (EZSP) host side.

EZSP is the command protocol used by a host application processor to communicate with the EmberZNet PRO stack running on a Silicon Labs Network Co-Processor (NCP). The crate models the EZSP command/response surface, frame headers, parameter payloads, asynchronous callbacks, and the UART transport used by EZSP-UART NCP firmware.

Documentation Basis

The crate documentation is based on these Silicon Labs references:

The implementation keeps the legacy EZSP naming used throughout UG100 and the EmberZNet 6.x/7.x API surface where that naming is reflected in the crate.

Features

  • ashv2: enables the ASHv2 serial transport (uart::Uart).
  • apis-saltans: enables apis_saltans_hw integration for Ncp/Builder and pulls in apis-saltans APS/core/hardware/ZDP crates.
  • semver: enables semver support for EZSP version APIs.

Protocol Model

EZSP messages are exchanged between a host and an NCP over SPI or UART. This crate currently provides the UART path via ASHv2.

  • The host starts normal EZSP use by sending the version command after NCP reset. A successful version transaction establishes the protocol version that both sides will use.
  • EZSP fields wider than one byte are serialized little-endian, including EUI64 values.
  • Frames contain a sequence number, frame control, frame ID, and typed parameters. EZSP protocol versions before 8 use a three-byte legacy header; versions 8 and newer use the extended five-byte header.
  • Most commands form a two-message transaction: host command, then NCP response. UART NCPs may also send callbacks asynchronously as they occur.
  • The response frame control reports NCP status bits such as overflow, truncation, callback-pending state, and callback type.

UART and ASHv2

UG101 describes ASH as the data-link layer below EZSP and above the serial driver. ASHv2 frames add reliability around EZSP payloads: CRC validation, byte stuffing, data-field randomization, sliding-window acknowledgements, ACK/NAK frames, reset handling, and optional not-ready flow control.

EZSP and ASHv2 do not add a protocol-level fragmentation layer. On UART, one EZSP frame is carried in exactly one ASHv2 DATA payload, and one ASHv2 DATA payload is decoded as exactly one EZSP frame.

Defragmenter<T> reassembles APS-level fragmented unicasts for any T: Messaging. Its asynchronous handle method consumes each IncomingMessage, sends the empty sendReply required for fragments, and returns a Defragmented message once the payload is complete. The apis-saltans event handler owns a defragmenter backed by the same Arc<tokio::sync::Mutex<T>> as the NCP and emits incoming-message events only for complete APS payloads.

Reassembly follows the EZSP fragment window, keys messages by sender and APS sequence, bounds the payload to 4096 bytes, and expires incomplete messages after a five-second timeout. The compile-time environment variables EZSP_DEFRAGMENTATION_MAX_INCOMING_PACKETS, EZSP_DEFRAGMENTATION_DEFAULT_WINDOW_SIZE, EZSP_DEFRAGMENTATION_RECEIVE_BUFFER_LENGTH, and EZSP_DEFRAGMENTATION_REASSEMBLY_TIMEOUT_MILLIS override these defaults.

The ashv2 feature delegates this link layer to the ashv2 crate and keeps the EZSP-specific work in this crate:

  • uart::Encoder serializes EZSP headers and parameters into ASHv2 payloads.
  • uart::Decoder parses ASHv2 payloads back into typed EZSP frames.
  • uart::Splitter routes normal responses to the pending request path and UART asynchronous callbacks to the callback channel. Its future returns an error if one of those destination channels closes before the splitter finishes.
  • uart re-exports the ASHv2 types and helpers used by the public transport API: FlowControl, Handle, NativeSerialPort, Payload, SerialPort, open, and start.

Core API

The crate is transport-first:

  • Transport defines the low-level async connection and request/response primitives.
  • Communicate defines connection checking and typed command/response transactions.
  • Arc<tokio::sync::Mutex<T>> implements Communicate when T does, providing cloneable, asynchronously serialized access to one communicator.
  • EZSP command traits (Configuration, Messaging, Networking, Security, ...) are blanket-implemented for any T: Communicate.
  • Ezsp is a convenience trait that combines all command traits.
  • Ncp<T> wraps a communicator and adds host-side NCP helpers for scans, APS send confirmation, transaction/message sequence counters, and callback correlation.
  • Protocol types are exposed through ember, ezsp, and the typed frame/parameter model.

Every Transport receives a blanket Communicate implementation, which gives it access to the full typed command surface.

ashv2 transport

The crate currently ships one concrete transport implementation: uart::Uart (feature = "ashv2").

Uart provides:

  • protocol negotiation through Transport::connect() and connection checking through Communicate::ensure_connection()
  • typed EZSP request/response handling over ASHv2 payload framing
  • response/callback demultiplexing
  • caller-driven transport futures through uart::Futures
  • serial constructors:
    • Uart::open(path, flow_control, protocol_version, &ChannelSizes) returns (Uart, callbacks, Futures<_>)
    • Uart::from_serial_port(serial_port, protocol_version, &ChannelSizes) returns (Uart, callbacks, Futures<_>)
    • Uart::new(handle, ash_rx, callbacks_tx, protocol_version, channel_size) returns (Uart, splitter_future) for advanced integration. The splitter future resolves to std::io::Result<()>.

Additional types:

  • uart::ChannelSizes to tune queue capacities for Uart::open / from_serial_port
  • uart::Buffers for ASHv2 queue sizing in integration helper constructors
  • uart::Futures for the serial worker, ASHv2 transmitter/receiver, and EZSP frame splitter futures that the caller must poll or spawn. The frame splitter future resolves to std::io::Result<()>.
  • uart::SerialPort, uart::FlowControl, and the other re-exported ASHv2 items needed to integrate the UART transport without importing ashv2 paths directly

Minimal ashv2 usage

use ezsp::uart::{ChannelSizes, SerialPort, Uart};
use ezsp::{Communicate, Utilities};
use tokio::task::LocalSet;

// Requires feature = "ashv2"
// Requires a Tokio runtime. The returned futures must be driven by the caller.
async fn example() -> Result<(), ezsp::Error> {
    let serial_port = /* your serial port implementing SerialPort */;
    let sizes = ChannelSizes::default();

    let (mut uart, _callbacks, futures) =
        Uart::from_serial_port(serial_port, ezsp::MIN_NON_LEGACY_VERSION, &sizes)?;

    let local = LocalSet::new();
    local.spawn_local(futures.serial_worker);
    local.spawn_local(futures.ash_transmitter);
    local.spawn_local(futures.ash_receiver);
    local.spawn_local(async move {
        futures
            .frame_splitter
            .await
            .expect("EZSP frame splitter failed");
    });

    local
        .run_until(async move {
            uart.ensure_connection().await?;
            let _eui64 = uart.get_eui64().await?;
            Ok(())
        })
        .await
}

NCP Helper

Ncp<T> is the high-level host helper for an EZSP Network Co-Processor. It owns a communicator and uses it for complete EZSP command/response transactions. The apis-saltans startup path connects the supplied transport, wraps it in Arc<tokio::sync::Mutex<T>>, and gives clones to the Ncp and its event handler. The Communicate implementation holds the mutex for one complete transaction and releases it before the NCP waits for asynchronous callbacks.

Ncp adds behavior that needs more than a single command/response exchange:

  • active and energy scans with callback aggregation,
  • neighbor table collection,
  • unicast and multicast APS sends with messageSent confirmation,
  • broadcast APS sends with immediate confirmation,
  • source endpoint selection for outgoing APS frames from the configured local endpoint output clusters,
  • message tag and APS sequence counters,
  • clean event-handler shutdown through Ncp::terminate().

Ncp::build(transport, callbacks) returns Builder<T>. The builder stores policies, configuration values, security keys, APS options, concentrator settings, network formation settings, and channel buffer sizing for the startup implementation.

Outgoing APS helper methods take the APS profile ID, cluster ID, destination endpoint, and message payload. They derive the source endpoint from the first configured local endpoint that advertises the cluster ID as an output cluster. If no endpoint matches, the send fails with Error::NoMatchingSourceEndpoint.

If ashv2 is enabled, Ncp::ashv2(serial_port) and Builder::<uart::Uart>::ashv2(serial_port) create a builder backed by the crate's ASHv2 UART transport. The serial port type is constrained by the re-exported uart::SerialPort trait. These constructors return the builder and the uart::Futures set that must be driven alongside the NCP.

apis-saltans Integration (apis-saltans Feature)

When apis-saltans is enabled, the crate adapts Ncp to the apis_saltans_hw driver traits and provides custom Builder startup helpers.

  • Ncp<T>: apis_saltans_hw::Driver when T: Messaging + Networking + Utilities + Send + Sync.
  • Builder::start(endpoints) configures the EZSP stack, starts callback translation, registers each SimpleDescriptor as an EZSP endpoint, stores the descriptor cluster lists for later source endpoint selection, spawns the NCP actor, and returns (apis_saltans_hw::NcpHandle, tokio::sync::mpsc::Receiver<apis_saltans_hw::Event>).
  • Ncp::terminate() stops the event handler.

The integration layer translates EZSP callbacks into apis_saltans_hw::Event, including network-up/down/open/closed events, child join/leave events, trust-center join/rejoin/leave events, and incoming APS messages. It also reassembles fragmented incoming APS messages, aggregates scan callbacks for Driver scan calls, and correlates messageSent callbacks with outgoing message tags. Outgoing Driver frames use the frame metadata for the APS profile and cluster; unicast calls use the requested destination endpoint, while multicast and broadcast calls use the profile's broadcast endpoint. Unicast sends target one destination endpoint per call; callers that need fan-out should issue multiple unicast requests.

Legal

This project is free software and is not affiliated with Silicon Labs. Silicon Labs documentation is cited only to describe the public protocol implemented by this crate.

Contribution guidelines

  • Format: cargo +nightly fmt
  • Lint: cargo clippy