Port Hubris ast1060-mctp-i2c-echo to OpenPRoT (Pigweed)

Context

Source: hubris/app/ast1060-mctp-i2c-echo/ A Hubris RTOS application running MCTP-over-I2C echo on an AST1060 RoT.

Task	Crate	Role
jefe	task-jefe	Supervisor / fault manager
idle	task-idle	Idle task
mctp_echo	mctp-echo	Listens for MCTP type-1 requests, echoes payload back
mctp_server	mctp-server	MCTP transport layer (features: serial_log, transport_i2c)
uart_driver	drv-ast1060-uart	UART peripheral driver
i2c_driver	drv-mock-i2c	Mock I2C driver (feature: mock-only)

Target: openprot/ Cargo workspace + Bazel, targeting the Pigweed kernel (pw_kernel). Existing services follow api/ + server/ + backend-*/ pattern (see services/i2c/). Platform integration is Pigweed-only — the MCTP server will run as a userspace process under pw_kernel, not a Hubris task or Linux process.

Porting Principle

Preserve as much of the original Hubris code as possible. Only change what is OS-dependent. The MCTP protocol logic, packet handling, server state management, transport encoding/decoding, and application logic (echo) should be carried over as-is. The only parts that change are:

• IPC mechanism: Hubris idol / sys_reply / Leased → Pigweed pw_kernel IPC/channels
• Task/process model: Hubris task_slot! / sys_recv_open / notifications → Pigweed userspace process event loop
• Driver APIs: Hubris drv-i2c-api / ast1060-uart-api → OpenPRoT services/i2c/ userspace driver
• Build system: Hubris app.toml + build.rs code generation → Bazel BUILD files + system.json5

Everything else — the Server struct, Router integration, Sender implementations, handle management, timeout logic, MCTP type definitions — should remain structurally identical to the Hubris originals.

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Phase 1: MCTP Service API (services/mctp/api) — COMPLETE

Create the platform-independent MCTP types and traits crate.

• [x] Create services/mctp/api/ directory structure
• [x] Cargo.toml — openprot-mctp-api crate
• [x] src/lib.rs — Handle, RecvMetadata types
• [x] src/error.rs — ResponseCode, MctpError (ported from hubris mctp-api ServerError)
• [x] src/traits.rs — MctpClient, MctpListener, MctpReqChannel, MctpRespChannel
• [x] Add to workspace Cargo.toml
• [x] Verify cargo check passes

Phase 2: MCTP Server Core (services/mctp/server) — COMPLETE

Create the platform-independent server logic crate.

• [x] Create services/mctp/server/ directory structure
• [x] Cargo.toml — openprot-mctp-server crate
• [x] src/lib.rs + src/server.rs — Server struct with EID mgmt, pending recv tracking, timeouts
• [x] Add to workspace Cargo.toml
• [x] Verify cargo check passes
• [x] Integrate mctp-stack (mctp-lib) Router as the packet processing engine
• [x] Re-export mctp_stack::Sender trait for transport bindings
• [x] Wire up inbound packet → Router → pending recv fulfillment via Server::inbound() + Server::update()

Phase 3: I2C Transport Binding (services/mctp/transport-i2c) — COMPLETE

Port the I2C transport from hubris mctp-server/src/i2c.rs, using the I2C userspace driver at services/i2c/ as the underlying transport.

• [x] Create services/mctp/transport-i2c/ crate
• [x] Implement Sender for I2C using the services/i2c/ userspace driver (client API + IPC to I2C server)
• [x] Implement inbound I2C → MCTP packet decoding (using mctp-stack::i2c::MctpI2cHandler)
• [x] Use I2cTargetClient from services/i2c/api for slave/target mode receive
• [x] Echo integration test with client/server partition (DirectClient implementing MctpClient, 2 tests passing)

Phase 4: Serial Transport Binding (services/mctp/transport-serial) — NOT STARTED

Port the serial transport from hubris mctp-server/src/serial.rs. (Lower priority than I2C.)

• [ ] Create services/mctp/transport-serial/ crate
• [ ] Implement Sender for serial (using embedded-io::Write, not hubris ast1060-uart-api)
• [ ] Implement inbound serial → MCTP packet decoding (using mctp-stack::serial::MctpSerialHandler)

Phase 5: MCTP Echo Application — IN PROGRESS

Port the echo task from hubris task/mctp-echo/.

• [x] IPC wire protocol (services/mctp/api/src/wire.rs) — request/response encoding for all MCTP operations
• [x] IPC client (services/mctp/client/) — IpcMctpClient implementing MctpClient via wire protocol + IPC
• [x] Server-side IPC dispatch (services/mctp/server/src/dispatch.rs) — decodes wire requests, calls Server
• [x] Wire-protocol dispatch integration test (tests/dispatch.rs) — full round-trip through wire encoding
• [x] Echo binary as Pigweed userspace process (target/ast1060-evb/mctp/mctp_echo.rs)
• [ ] Wire up with server + I2C transport for an end-to-end demo (needs real I2C sender in server main.rs)

Phase 6: Pigweed Platform Integration — MOSTLY DONE

Wire up the MCTP server as a Pigweed userspace process on the AST1060-EVB (target/ast1060-evb/).

• [x] MCTP server main.rs: event loop driven by pw_kernel IPC/channels
  • Replaces hubris sys_recv_open / notifications / idol IPC dispatch
  • Uses dispatch_mctp_op for IPC request handling
  • Follows the pattern established by services/i2c/server/
  • Uses NoopSender for initial bring-up; real I2cSender wiring is TODO
• [x] Connect IpcMctpClient::send_recv to syscall::channel_transact (gated behind pigweed feature)
• [x] Bazel BUILD files for each new crate (following services/i2c/ pattern)
• [x] system.json5 entry for MCTP server + echo processes (target/ast1060-evb/mctp/)
• [x] Integration with target/ast1060-evb/ platform definition (target.rs, BUILD.bazel)

Phase 7: Testing & Documentation — PARTIALLY DONE

• [x] Wire protocol unit tests (7 tests in api/src/wire.rs)
• [x] Echo integration tests with client/server partition (2 tests in server/tests/echo.rs)
• [x] Wire-protocol dispatch integration tests (2 tests in server/tests/dispatch.rs)
• [x] README for each MCTP crate (api/, server/, client/, transport-i2c/)
• [ ] QEMU-based end-to-end test (following services/i2c/ test pattern)
• [ ] Update docs/src/specification/middleware/mctp.md with implementation status

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Current Status

Phases 1–3, 5, and 6 mostly complete. All library code, IPC dispatch, Bazel BUILD files, system configuration, and echo binary are written. 11 tests pass. Remaining work: wire up real I2cSender in server main.rs (replace NoopSender), QEMU e2e test, and docs update.

Key Dependencies

Crate	Source	Role
mctp	workspace (types crate)	Eid, MsgType, Tag, Error etc.
mctp-stack / mctp-lib	github.com/9elements/mctp-lib branch buildup	Router, Sender, fragmentation, serial/I2C handlers
services/i2c/	I2C userspace driver	I2C client/target/server — MCTP transport-i2c uses this as its underlying I2C transport
heapless	workspace	no_std collections
zerocopy	workspace	Zero-copy serialization
Pigweed (pw_kernel)	Bazel via MODULE.bazel	Userspace processes, IPC channels, system image