openprot-mctp-server

Platform-independent MCTP server core, ported from the Hubris mctp-server crate.

Overview

This crate implements the central MCTP server logic: listener and request handle allocation, inbound message routing, outbound message fragmentation/sending, and timeout management for pending receive calls. It is generic over transport bindings via the mctp_lib::Sender trait.

Key Types

Server<S, N> — the MCTP server, generic over Sender (transport) and N (config)
ServerConfig — configuration constants (MAX_REQUESTS: 8, MAX_LISTENERS: 8, MAX_OUTSTANDING: 16, MAX_PAYLOAD: 1023)
RecvResult — result from a receive operation

Modules

dispatch — IPC request dispatcher; decodes wire-protocol requests and calls the corresponding Server methods

Architecture

The server wraps the mctp-lib Router as its packet processing engine. Inbound packets are fed via Server::inbound(), and Server::update() drives pending-recv fulfillment. The dispatch module bridges IPC wire-protocol messages to server operations.

Dependencies

openprot-mctp-api — API traits and wire protocol
mctp-lib — Router, Sender, fragmentation, serial/I2C handlers
mctp — core MCTP types (Eid, MsgType, Tag)
heapless — no_std collections

Building the MCTP Echo System Image

The MCTP echo demo is a 3-application system image for the AST1060-EVB (640KB usable SRAM):

Flash (512KB)                              RAM (128KB)
0x00000 ┌─────────────────────┐  0x80000 ┌──────────────────┐
        │   pw_kernel (~128KB) │          │  i2c_server 32KB │
0x20000 ├─────────────────────┤  0x88000 ├──────────────────┤
        │   i2c_server  128KB  │          │ mctp_server 32KB │
0x40000 ├─────────────────────┤  0x90000 ├──────────────────┤
        │   mctp_server 128KB  │          │  mctp_echo  32KB │
0x60000 ├─────────────────────┤  0x98000 ├──────────────────┤
        │   mctp_echo   128KB  │          │   kernel    32KB │
0x80000 └─────────────────────┘  0xA0000 └──────────────────┘
                                          (640KB = 0xA0000)

App	Source	Role
`i2c_server`	`//services/i2c/server`	I2C transport backend
`mctp_server`	`//services/mctp/server`	MCTP router + IPC dispatcher
`mctp_echo`	`//target/ast1060-evb/mctp/mctp_echo.rs`	Listens for type-1 messages, echoes payload back

Build the full system image

bazel build --config=k_ast1060_evb //target/ast1060-evb/mctp:mctp

Build just the echo binary

bazel build --config=k_ast1060_evb //target/ast1060-evb/mctp:mctp_echo

Build a UART-bootable image (for physical EVB)

bazel build --config=k_ast1060_evb //target/ast1060-evb/mctp:mctp_uart

The output binary mctp_uart.bin can be flashed over the UART boot interface.

Run the system image test

bazel test --config=k_ast1060_evb //target/ast1060-evb/mctp:mctp_test

The mctp_test rule wraps the system image in a system_image_test harness that exercises the full kernel + I2C server + MCTP server + echo app stack.

Tests

The tests/ directory contains integration tests that run on the host (std) with no I2C transport — a BufferSender mock replaces it entirely.

Test files

File	What it tests
`tests/common/mod.rs`	Shared fixtures: `BufferSender`, `DroppingBufferSender`, `DirectClient`, `DirectListener`, `DirectRespChannel`, `DirectReqChannel`
`tests/echo.rs`	Full MCTP echo round-trip via `MctpClient` trait
`tests/dispatch.rs`	IPC wire-protocol dispatch: encodes requests, calls `dispatch_mctp_op`, verifies responses. Includes edge cases: malformed request, unknown opcode, `Recv` with no message, `Unbind`
`tests/server_unit.rs`	Unit tests for `Server` methods: EID management, handle allocation, `try_recv` before/after `inbound`, oversized payload, timeout via `register_recv` + `update`
`tests/integration.rs`	Multi-fragment reassembly, multiple concurrent listeners (no cross-talk), echo via `MctpListener` + `MctpRespChannel` traits, `MctpReqChannel` trait, `drop_handle` mid-flight, response EID/tag threading

The echo via MctpListener + MctpRespChannel test (echo_via_mctplistener_trait) is the key one: it exercises the exact interface the real echo application uses, with BufferSender as the only transport.

Running with Bazel

# Run all test targets
bazel test //services/mctp/server:mctp_server_echo_test \
           //services/mctp/server:mctp_server_dispatch_test \
           //services/mctp/server:mctp_server_unit_test \
           //services/mctp/server:mctp_server_integration_test

# Show test output
bazel test //services/mctp/server:mctp_server_unit_test --test_output=all

Note: Do not use the //services/mctp/... wildcard — it will also pick up the mctp_server and mctp_echo kernel binaries, which require kernel_config (generated only during a full system image build). Target the test rules directly as shown above.