MCTP & PLDM Guide

Configure and use MCTP and PLDM protocols on OpenBMC.

Overview
1. Why MCTP/PLDM?
2. Protocol Stack
MCTP Protocol Deep Dive
MCTP Transport Bindings
PLDM Protocol Deep Dive
Platform Data Records (PDR)
OpenBMC Implementation
Setup & Configuration
MCTP Configuration
PLDM Configuration
Device Integration Examples
PLDM Firmware Update
1. Firmware Update Flow
2. Firmware Update Commands
Event Handling
D-Bus Interfaces
1. MCTP D-Bus Objects
2. PLDM D-Bus Objects
Troubleshooting
Security Considerations
Enabling/Disabling
1. Build-Time Disable
2. Runtime Disable
Examples
References
Deep Dive

Overview

MCTP (Management Component Transport Protocol) and PLDM (Platform Level Data Model) are DMTF standards for platform management communication. They provide a modern, scalable alternative to IPMI for device-to-device management in data center environments.

Why MCTP/PLDM?

Feature	IPMI	MCTP/PLDM
Message size	256 bytes max	64KB+
Transport	KCS, BT, IPMB	I2C, PCIe, SMBus, USB, Serial
Extensibility	OEM codes	Typed messages with PDR
Discovery	Manual	Automatic endpoint discovery
Sensors	SDR-based	PDR with rich metadata
Security	Limited	SPDM integration

Protocol Stack

---
title: MCTP/PLDM Protocol Stack
---
flowchart TB
    subgraph app["Application Layer"]
        direction TB
        pldm["PLDM Types<br/>0,2,3,4,5"]
        spdm["SPDM<br/>Security"]
        ncsi["NCSI<br/>Network Control"]
        nvme["NVMe-MI<br/>Storage Mgmt"]
    end

    app --> transport

    subgraph transport["MCTP Transport Layer"]
        direction TB
        assembly["Message Assembly<br/>& Fragmentation"]
        routing["Packet Routing<br/>& Forwarding"]
        eid["EID Management<br/>& Discovery"]
    end

    transport --> physical

    subgraph physical["Physical Transport Bindings"]
        direction TB
        i2c["I2C<br/>DSP0237"]
        smbus["SMBus<br/>DSP0237"]
        pcie["PCIe<br/>DSP0238"]
        serial["Serial<br/>DSP0239"]
        usb["USB<br/>DSP0283"]
    end

ASCII-art version (for comparison)

+-------------------------------------------------------------------------+
|                    MCTP/PLDM Protocol Stack                             |
+-------------------------------------------------------------------------+
|                                                                         |
|   +------------------------------------------------------------------+  |
|   |                    Application Layer                             |  |
|   |                                                                  |  |
|   |   +----------+  +----------+  +----------+  +----------+         |  |
|   |   |  PLDM    |  |  SPDM    |  |  NCSI    |  |  NVMe-MI |         |  |
|   |   | Types    |  | Security |  | Network  |  | Storage  |         |  |
|   |   | 0,2,3,4,5|  |          |  | Control  |  | Mgmt     |         |  |
|   |   +----------+  +----------+  +----------+  +----------+         |  |
|   +------------------------------------------------------------------+  |
|                                    |                                    |
|   +------------------------------------------------------------------+  |
|   |                    MCTP Transport Layer                          |  |
|   |                                                                  |  |
|   |   +------------------+  +------------------+  +-----------------+|  |
|   |   | Message Assembly |  | Packet Routing   |  | EID Management  ||  |
|   |   | & Fragmentation  |  | & Forwarding     |  | & Discovery     ||  |
|   |   +------------------+  +------------------+  +-----------------+|  |
|   +------------------------------------------------------------------+  |
|                                    |                                    |
|   +------------------------------------------------------------------+  |
|   |                    Physical Transport Bindings                   |  |
|   |                                                                  |  |
|   |   +--------+  +--------+  +--------+  +--------+  +--------+     |  |
|   |   | I2C    |  | SMBus  |  | PCIe   |  | Serial |  | USB    |     |  |
|   |   | DSP0237|  | DSP0237|  | DSP0238|  | DSP0239|  | DSP0283|     |  |
|   |   +--------+  +--------+  +--------+  +--------+  +--------+     |  |
|   +------------------------------------------------------------------+  |
|                                                                         |
+-------------------------------------------------------------------------+

MCTP Protocol Deep Dive

MCTP Packet Format

Every MCTP packet follows this structure:

+-------+-------+-------+-------+-------+-------+-------+-------+
| Byte 0        | Byte 1        | Byte 2        | Byte 3        |
+---------------+---------------+---------------+---------------+
| Header Ver(4) | Dest EID (8)  | Source EID(8) | SOM|EOM|PktSeq|
| Rsvd (4)      |               |               | TO |Tag (3)   |
+---------------+---------------+---------------+---------------+
|                    Message Payload                            |
|                    (variable length)                          |
+---------------------------------------------------------------+
|                    Integrity Check (optional)                 |
+---------------------------------------------------------------+

Header Fields

Field	Bits	Description
Header Version	4	Always 0x1 for MCTP v1.x
Reserved	4	Must be 0
Destination EID	8	Target endpoint ID (0x00-0xFF)
Source EID	8	Sender endpoint ID
SOM	1	Start of Message flag
EOM	1	End of Message flag
Packet Sequence	2	Sequence number for fragmentation
TO	1	Tag Owner (1=requester, 0=responder)
Message Tag	3	Unique tag per outstanding request

Special Endpoint IDs

EID	Name	Purpose
0x00	Null EID	Unassigned endpoint
0x01-0x07	Reserved	Reserved by DMTF
0x08	Default BMC	Common BMC address
0x09-0xFE	General	Assignable to endpoints
0xFF	Broadcast	All endpoints on network

MCTP Message Types

Type	Value	Description	Specification
MCTP Control	0x00	Endpoint management	DSP0236
PLDM	0x01	Platform management	DSP0240
NCSI	0x02	Network controller	DSP0222
Ethernet	0x03	Ethernet frames	DSP0236
NVMe-MI	0x04	NVMe management	NVM Express
SPDM	0x05	Security protocol	DSP0274
Secure SPDM	0x06	Secured SPDM	DSP0277
Vendor Defined (PCI)	0x7E	PCI vendor ID	DSP0236
Vendor Defined (IANA)	0x7F	IANA enterprise	DSP0236

MCTP Control Messages

MCTP Control (type 0x00) manages the MCTP network:

MCTP Control Message Format:
+-------+-------+-------+-------+
| IC|MsgType(7)| RqDI| Command |
| (1)          | (1) |Instance |
|              |     | ID (5)  |
+-------+-------+-------+-------+
|          Command Data         |
+-------------------------------+

Control Commands

Command	Code	Description
Set Endpoint ID	0x01	Assign EID to endpoint
Get Endpoint ID	0x02	Query endpoint’s EID
Get Endpoint UUID	0x03	Get unique identifier
Get MCTP Version	0x04	Query MCTP version support
Get Message Type Support	0x05	Query supported message types
Get Vendor Defined Message Support	0x06	Query vendor extensions
Resolve Endpoint ID	0x07	Map EID to physical address
Allocate Endpoint IDs	0x08	Request EID pool
Routing Information Update	0x09	Update routing tables
Get Routing Table Entries	0x0A	Query routing table
Prepare Endpoint Discovery	0x0B	Reset discovery state
Endpoint Discovery	0x0C	Discover endpoints
Discovery Notify	0x0D	Notify discovery complete

Message Fragmentation

MCTP fragments large messages across multiple packets:

Large Message (> MTU):
+------------------+------------------+------------------+
|  Packet 1        |  Packet 2        |  Packet 3        |
|  SOM=1, EOM=0    |  SOM=0, EOM=0    |  SOM=0, EOM=1    |
|  Seq=0           |  Seq=1           |  Seq=2           |
|  [Payload 1]     |  [Payload 2]     |  [Payload 3]     |
+------------------+------------------+------------------+

Reassembled at receiver:
+----------------------------------------------------------+
|  Complete Message = Payload 1 + Payload 2 + Payload 3    |
+----------------------------------------------------------+

MTU by Transport

Transport	Minimum MTU	Typical MTU
I2C/SMBus	64 bytes	64-256 bytes
PCIe VDM	64 bytes	64-4096 bytes
Serial	64 bytes	64-256 bytes
USB	64 bytes	512 bytes

MCTP Transport Bindings

I2C/SMBus Binding (DSP0237)

I2C MCTP Packet Structure:
+-------+-------+-------+-------+-------+-------+-------+
| Slave | Cmd   | Byte  | Src   | Hdr   | MCTP Header   |
| Addr  | Code  | Count | Addr  | Ver   | + Payload     |
| (7+1) | 0x0F  | (8)   | (7+1) | (4+4) |               |
+-------+-------+-------+-------+-------+---------------+
|                    Payload Data                       |
+-------------------------------------------------------+
| PEC (optional)                                        |
+-------------------------------------------------------+

I2C Configuration

# Create MCTP I2C interface
mctp link add mctpi2c1 type i2c bus 1

# Set interface up
mctp link set mctpi2c1 up

# Set local address
mctp addr add 8 dev mctpi2c1

# Verify configuration
mctp link show
mctp addr show

Device Tree for I2C MCTP

&i2c1 {
    status = "okay";

    /* MCTP-capable device at address 0x50 */
    mctp_device@50 {
        compatible = "mctp-i2c-controller";
        reg = <0x50>;
    };
};

PCIe VDM Binding (DSP0238)

PCIe Vendor Defined Messages carry MCTP over PCIe:

PCIe VDM TLP Format:
+-------+-------+-------+-------+
| Fmt   | Type  | TC    | Attr  |  <- TLP Header
| (3)   | (5)   | (3)   | (2)   |
+-------+-------+-------+-------+
| Length        | Requester ID  |
+---------------+---------------+
| Tag   | Message Code          |  <- VDM Header
| (8)   | Vendor ID (16)        |
+-------+-----------------------+
| MCTP Transport Header         |  <- MCTP Packet
+-------------------------------+
| MCTP Payload                  |
+-------------------------------+

PCIe VDM Configuration

# PCIe MCTP typically auto-discovered
# Check for PCIe MCTP devices
lspci -vvv | grep -i mctp

# MCTP over PCIe uses kernel MCTP stack
mctp link

Serial Binding (DSP0239)

Serial MCTP Frame:
+-------+-------+-------+-------+-------+
| Sync  | Rev   | Byte  | MCTP Packet   |
| 0x7E  | (8)   | Count |               |
+-------+-------+-------+---------------+
| FCS (16-bit CRC)                      |
+---------------------------------------+

PLDM Protocol Deep Dive

PLDM Message Format

PLDM Message Structure:
+-------+-------+-------+-------+-------+-------+-------+
| MCTP  |PLDM Hdr       | PLDM Payload                  |
| Msg   |               |                               |
| Type  |               |                               |
| 0x01  |               |                               |
+-------+-------+-------+-------------------------------+

PLDM Header:
+-------+-------+-------+-------+
| Rq|D|IID(5)   | Hdr   | PLDM  |
| (1)(1)        | Ver(2)| Type  |
|               |       | (6)   |
+---------------+-------+-------+
| Command Code (8)              |
+-------------------------------+

Header Fields

Field	Bits	Description
Rq (Request)	1	1=Request, 0=Response
D (Datagram)	1	1=No response expected
Instance ID	5	Request/response correlation
Header Version	2	Always 0b00
PLDM Type	6	Message type (0-63)
Command Code	8	Type-specific command

PLDM Types

Type	Name	Specification	Description
0	Base	DSP0240	Discovery, TID, versions
1	SMBIOS	DSP0246	SMBIOS table transfer
2	Monitoring & Control	DSP0248	Sensors, effecters, events
3	BIOS Control	DSP0247	BIOS attributes
4	FRU Data	DSP0257	Field Replaceable Unit data
5	Firmware Update	DSP0267	Firmware update protocol
6	Redfish Device Enablement	DSP0218	Redfish over PLDM
63	OEM	-	Vendor-specific

PLDM Type 0: Base Commands

Command	Code	Description
SetTID	0x01	Set Terminus ID
GetTID	0x02	Get Terminus ID
GetPLDMVersion	0x03	Query PLDM type versions
GetPLDMTypes	0x04	Query supported PLDM types
GetPLDMCommands	0x05	Query commands for a type
SelectPLDMVersion	0x06	Negotiate version
NegotiateTransferParameters	0x07	Set transfer sizes
MultipartSend	0x08	Send large data
MultipartReceive	0x09	Receive large data

Example: Get TID

# Request GetTID (Command 0x02)
pldmtool raw -m 9 -d 0x80 0x00 0x02

# Response format:
# [0]: Completion Code (0x00 = success)
# [1]: TID value

PLDM Type 2: Monitoring & Control

This type handles sensors, effecters, and events.

Sensor Commands

Command	Code	Description
GetSensorReading	0x11	Read numeric sensor
GetSensorThresholds	0x12	Get threshold values
SetSensorThresholds	0x13	Set threshold values
RestoreSensorThresholds	0x14	Restore defaults
GetSensorHysteresis	0x15	Get hysteresis value
SetSensorHysteresis	0x16	Set hysteresis value
InitNumericSensor	0x17	Initialize sensor
GetStateSensorReading	0x21	Read state sensor

Effecter Commands

Command	Code	Description
SetNumericEffecterValue	0x31	Set numeric effecter
GetNumericEffecterValue	0x32	Get numeric effecter value
SetStateEffecterStates	0x39	Set state effecter
GetStateEffecterStates	0x3A	Get state effecter

Event Commands

Command	Code	Description
PlatformEventMessage	0x0A	Send platform event
PollForPlatformEventMessage	0x0B	Poll for events
EventMessageSupported	0x0C	Query event support
EventMessageBufferSize	0x0D	Query buffer size

PLDM Type 5: Firmware Update

Command	Code	Description
QueryDeviceIdentifiers	0x01	Get device IDs
GetFirmwareParameters	0x02	Get FW info
RequestUpdate	0x10	Start update
PassComponentTable	0x13	Send component list
UpdateComponent	0x14	Update single component
RequestFirmwareData	0x15	Request FW chunk
TransferComplete	0x16	Transfer done
VerifyComplete	0x17	Verification done
ApplyComplete	0x18	Application done
ActivateFirmware	0x1A	Activate new FW
GetStatus	0x1B	Query update status
CancelUpdateComponent	0x1C	Cancel component update
CancelUpdate	0x1D	Cancel entire update

Platform Data Records (PDR)

PDRs describe the platform’s sensors, effecters, and associations.

PDR Structure

PDR Header (common to all PDRs):
+-------+-------+-------+-------+-------+-------+-------+-------+
| Record Handle (32 bits)                                       |
+---------------+---------------+---------------+---------------+
| PDR Hdr Ver(8)| PDR Type (8)  | Record Change#| Data Len (16) |
+---------------+---------------+---------------+---------------+
|                    PDR-specific data                          |
+---------------------------------------------------------------+

PDR Types

Type	Name	Description
1	Terminus Locator	Maps TID to MCTP EID
2	Numeric Sensor	Numeric sensor definition
3	Numeric Sensor Initialization	Init parameters
4	State Sensor	State sensor definition
5	State Sensor Initialization	Init parameters
6	Sensor Auxiliary Names	Sensor name strings
9	OEM Device	Vendor-specific device
10	OEM	Vendor-specific PDR
11	Numeric Effecter	Numeric effecter definition
12	Numeric Effecter Initialization	Init parameters
13	State Effecter	State effecter definition
14	State Effecter Initialization	Init parameters
15	Effecter Auxiliary Names	Effecter name strings
20	Entity Association	Entity hierarchy
21	Entity Auxiliary Names	Entity name strings
22	OEM Entity ID	Vendor entity types

Numeric Sensor PDR Example

Numeric Sensor PDR (Type 2):
+-------+-------+-------+-------+-------+-------+-------+-------+
| Terminus Handle (16) | Sensor ID (16)                         |
+---------------+---------------+---------------+---------------+
| Entity Type(16)       | Entity Instance (16)                  |
+---------------+---------------+---------------+---------------+
| Container ID (16)     | Sensor Init | Auxiliary Names         |
+---------------+---------------+---------------+---------------+
| Base Unit (8)         | Unit Modifier (8) | Rate Unit (8)     |
+-----------------------+-----------------------+---------------+
| ... additional fields for ranges, thresholds, etc.            |
+---------------------------------------------------------------+

State Sets

State sensors/effecters use predefined state sets:

State Set ID	Name	Example States
1	Health State	Normal, Warning, Critical
2	Availability	Available, Unavailable
3	Operational Status	Enabled, Disabled
4	Configuration State	Valid, Invalid
11	Link State	Up, Down
15	Power Device	On, Off, Powering On, Powering Off
192	Boot Progress	Primary Processor Init, Memory Init, PCI Init
196	System Power State	Off, On, Standby

Querying PDRs

# Get all PDRs
pldmtool platform getpdr -t all -m 9

# Get specific PDR types
pldmtool platform getpdr -t numericSensorPDR -m 9
pldmtool platform getpdr -t stateSensorPDR -m 9
pldmtool platform getpdr -t numericEffecterPDR -m 9
pldmtool platform getpdr -t stateEffecterPDR -m 9
pldmtool platform getpdr -t terminusLocatorPDR -m 9
pldmtool platform getpdr -t entityAssociationPDR -m 9

# Get PDR by record handle
pldmtool platform getpdr -d 1 -m 9
pldmtool platform getpdr -d 2 -m 9

OpenBMC Implementation

Architecture

---
title: OpenBMC MCTP/PLDM Architecture
---
flowchart TB
    subgraph dbus_services["D-Bus Services"]
        direction LR
        sensors["Sensor Service<br/>(dbus-sensors)"]
        statemgr["State Manager<br/>(phosphor-state-mgr)"]
        fwupdate["Firmware Update<br/>(phosphor-bmc-code-mgmt)"]
    end

    subgraph dbus_layer["D-Bus"]
        dbus_ns["xyz.openbmc_project.PLDM<br/>xyz.openbmc_project.MCTP"]
    end

    subgraph pldmd_layer["pldmd"]
        direction TB
        pldm_req["PLDM Requester<br/>(host comms)"]
        pldm_resp["PLDM Responder<br/>(BMC as target)"]
        pdr_mgr["PDR Manager<br/>(PDR repository)"]
        libpldm["libpldm<br/>(PLDM message encode/decode, PDR parsing)"]
    end

    subgraph mctpd_layer["mctpd"]
        direction TB
        route_mgr["Route Manager"]
        eid_pool["EID Pool<br/>Manager"]
        link_mgmt["Link Management"]
        libmctp["libmctp<br/>(MCTP packet handling, transport bindings)"]
    end

    subgraph kernel_layer["Linux Kernel MCTP Stack"]
        direction LR
        af_mctp["AF_MCTP Socket"]
        mctp_net["MCTP Network<br/>Device"]
        transport["Transport Drivers<br/>(i2c-mctp, etc.)"]
    end

    dbus_services --> dbus_layer
    dbus_layer --> pldmd_layer
    pldmd_layer --> mctpd_layer
    mctpd_layer --> kernel_layer

ASCII-art version (for comparison)

+-------------------------------------------------------------------------+
|                    OpenBMC MCTP/PLDM Architecture                       |
+-------------------------------------------------------------------------+
|                                                                         |
|   +------------------------------------------------------------------+  |
|   |                      D-Bus Services                              |  |
|   |                                                                  |  |
|   |   +---------------+  +---------------+  +------------------+     |  |
|   |   | Sensor Service|  | State Manager |  | Firmware Update  |     |  |
|   |   | (dbus-sensors)|  | (phosphor-    |  | (phosphor-bmc-   |     |  |
|   |   |               |  |  state-mgr)   |  |  code-mgmt)      |     |  |
|   |   +-------+-------+  +-------+-------+  +---------+--------+     |  |
|   +-----------|------------------|---------------------|-------------+  |
|               |                  |                     |                |
|   +-----------+------------------+---------------------+-------------+  |
|   |                         D-Bus                                    |  |
|   |    xyz.openbmc_project.PLDM    xyz.openbmc_project.MCTP          |  |
|   +----------------------------------+-------------------------------+  |
|                                      |                                  |
|   +----------------------------------+-------------------------------+  |
|   |                           pldmd                                  |  |
|   |                                                                  |  |
|   |   +----------------+  +---------------+  +------------------+    |  |
|   |   | PLDM Requester |  | PLDM Responder|  | PDR Manager      |    |  |
|   |   | (host comms)   |  |(BMC as target)|  | (PDR repository) |    |  |
|   |   +----------------+  +---------------+  +------------------+    |  |
|   |                                                                  |  |
|   |   +----------------------------------------------------------+   |  |
|   |   |                       libpldm                            |   |  |
|   |   |  (PLDM message encode/decode, PDR parsing)               |   |  |
|   |   +----------------------------------------------------------+   |  |
|   +----------------------------------+-------------------------------+  |
|                                      |                                  |
|   +----------------------------------+-------------------------------+  |
|   |                           mctpd                                  |  |
|   |                                                                  |  |
|   |   +----------------+  +---------------+  +------------------+    |  |
|   |   | Route Manager  |  | EID Pool      |  | Link Management  |    |  |
|   |   |                |  | Manager       |  |                  |    |  |
|   |   +----------------+  +---------------+  +------------------+    |  |
|   |                                                                  |  |
|   |   +----------------------------------------------------------+   |  |
|   |   |                       libmctp                            |   |  |
|   |   |  (MCTP packet handling, transport bindings)              |   |  |
|   |   +----------------------------------------------------------+   |  |
|   +----------------------------------+-------------------------------+  |
|                                      |                                  |
|   +----------------------------------+-------------------------------+  |
|   |                    Linux Kernel MCTP Stack                       |  |
|   |                                                                  |  |
|   |   +----------------+  +---------------+  +------------------+    |  |
|   |   | AF_MCTP Socket |  | MCTP Network  |  | Transport Drivers|    |  |
|   |   |                |  | Device        |  | (i2c-mctp, etc.) |    |  |
|   |   +----------------+  +---------------+  +------------------+    |  |
|   +------------------------------------------------------------------+  |
|                                                                         |
+-------------------------------------------------------------------------+

libmctp

Low-level MCTP packet handling:

// Key libmctp structures
struct mctp;                    // MCTP context
struct mctp_binding;            // Transport binding
struct mctp_pktbuf;             // Packet buffer

// Transport bindings
struct mctp_binding_i2c;        // I2C/SMBus
struct mctp_binding_astlpc;     // ASPEED LPC
struct mctp_binding_serial;     // Serial

// Key functions
mctp_init();                    // Initialize context
mctp_set_rx_all();              // Set receive callback
mctp_message_tx();              // Transmit message
mctp_binding_set_tx_enabled();  // Enable transmission

libpldm

PLDM message encoding and decoding:

// Request encoding
encode_get_tid_req(instance_id, &request);
encode_get_sensor_reading_req(instance_id, sensor_id, &request);
encode_set_state_effecter_states_req(instance_id, effecter_id, ...);

// Response decoding
decode_get_tid_resp(response, &tid, &completion_code);
decode_get_sensor_reading_resp(response, &reading, &status);

// PDR handling
pldm_pdr_init();                    // Initialize PDR repository
pldm_pdr_add();                     // Add PDR record
pldm_pdr_find_record();             // Find PDR by handle
pldm_entity_association_tree_init();// Entity tree

pldmd Configuration

// /usr/share/pldm/host_eid
9

// /usr/share/pldm/pdr/pdr.json
{
    "entries": [
        {
            "type": "terminusLocator",
            "data": {
                "terminusHandle": 1,
                "validity": "valid",
                "tid": 1,
                "containerID": 0,
                "terminusLocatorType": "mctp_eid",
                "terminusLocatorValue": 8
            }
        }
    ]
}

Setup & Configuration

Build-Time Configuration (Yocto)

# In your machine .conf or local.conf

# Include MCTP/PLDM components
IMAGE_INSTALL:append = " \
    mctp \
    mctpd \
    libpldm \
    pldm \
"

# Configure MCTP transport options
EXTRA_OEMESON:pn-mctpd = " \
    -Di2c=enabled \
    -Dastlpc=enabled \
    -Dserial=disabled \
"

# Configure PLDM options
EXTRA_OEMESON:pn-pldm = " \
    -Dtransport-implementation=af-mctp \
    -Doem-ibm=disabled \
    -Dsoftoff=enabled \
    -Dhost-eid=9 \
    -Dlibpldmresponder=enabled \
"

Meson Build Options (pldm)

Option	Default	Description
`transport-implementation`	af-mctp	Transport (af-mctp or mctp-demux)
`oem-ibm`	disabled	IBM OEM PLDM extensions
`softoff`	enabled	Host soft power off via PLDM
`host-eid`	9	Default host endpoint ID
`libpldmresponder`	enabled	BMC as PLDM responder
`system-specific-bios-json`	disabled	Custom BIOS JSON location

Meson Build Options (mctpd)

Option	Default	Description
`i2c`	enabled	I2C/SMBus transport
`astlpc`	enabled	ASPEED LPC transport
`serial`	disabled	Serial transport
`tests`	disabled	Build unit tests

Kernel Configuration

# Enable MCTP in kernel
CONFIG_MCTP=y
CONFIG_MCTP_FLOWS=y

# Transport drivers
CONFIG_I2C_MCTP=m
CONFIG_MCTP_SERIAL=m

Runtime Configuration

# Check MCTP daemon status
systemctl status mctpd

# Check PLDM daemon status
systemctl status pldmd

# View logs
journalctl -u mctpd -f
journalctl -u pldmd -f

# Enable debug logging
systemctl edit pldmd
# Add: Environment="PLDM_VERBOSITY=debug"

MCTP Configuration

Managing MCTP Networks

# List all MCTP interfaces
mctp link

# Example output:
# dev        net  eid    up
# mctpi2c1   1    8      yes
# mctplpc0   2    8      yes

# Set interface up
mctp link set mctpi2c1 up

# Set interface down
mctp link set mctpi2c1 down

# View interface details
ip link show type mctp

Endpoint Management

# List all endpoints
mctp endpoint

# Add local endpoint address
mctp addr add 8 dev mctpi2c1

# Remove endpoint address
mctp addr del 8 dev mctpi2c1

# View endpoint routing
mctp route

Static Endpoint Configuration

Create /etc/mctp/static-endpoints.json:

{
    "endpoints": [
        {
            "name": "host",
            "type": "static",
            "eid": 9,
            "transport": {
                "type": "i2c",
                "bus": 1,
                "address": "0x50"
            }
        },
        {
            "name": "gpu0",
            "type": "static",
            "eid": 10,
            "transport": {
                "type": "i2c",
                "bus": 3,
                "address": "0x51"
            }
        },
        {
            "name": "nvme0",
            "type": "static",
            "eid": 11,
            "transport": {
                "type": "i2c",
                "bus": 4,
                "address": "0x52"
            }
        }
    ]
}

D-Bus Interface for MCTP

# List MCTP service
busctl tree xyz.openbmc_project.MCTP

# Get endpoint properties
busctl introspect xyz.openbmc_project.MCTP \
    /xyz/openbmc_project/mctp/1/9

# Watch for new endpoints
busctl monitor xyz.openbmc_project.MCTP

PLDM Configuration

PDR Repository

# List all PDRs
pldmtool platform getpdr -t all

# Count PDRs
pldmtool platform getpdr -t all | grep -c "recordHandle"

# Export PDRs to file
pldmtool platform getpdr -t all > /tmp/pdr_dump.txt

Common PLDM Commands

# === Base Commands (Type 0) ===

# Get terminus ID
pldmtool base getTID -m 9

# Get PLDM version for type 0
pldmtool base getPLDMVersion -m 9 -t 0

# Get supported PLDM types
pldmtool base getPLDMTypes -m 9

# Get commands for a PLDM type
pldmtool base getPLDMCommands -m 9 -t 0
pldmtool base getPLDMCommands -m 9 -t 2

# === Platform Commands (Type 2) ===

# Get numeric sensor reading
pldmtool platform getSensorReading -m 9 -i 1

# Get state sensor reading
pldmtool platform getStateSensorReadings -m 9 -i 5

# Set state effecter
pldmtool platform setStateEffecterStates -m 9 -i 1 -c 1 -d 1

# Get PDR by type
pldmtool platform getPDR -m 9 -t sensorPDR
pldmtool platform getPDR -m 9 -t effecterPDR

# === Firmware Update Commands (Type 5) ===

# Get firmware parameters
pldmtool fw_update GetFirmwareParameters -m 9

# Query device identifiers
pldmtool fw_update QueryDeviceIdentifiers -m 9

Raw PLDM Commands

# Send raw PLDM command
# Format: pldmtool raw -m <eid> -d <byte1> <byte2> ...
# Byte format: 0xRR 0xTT 0xCC [payload...]
#   RR = Request/Instance (0x80 for request, IID=0)
#   TT = PLDM Type
#   CC = Command Code

# GetTID (Type 0, Command 0x02)
pldmtool raw -m 9 -d 0x80 0x00 0x02

# GetPLDMTypes (Type 0, Command 0x04)
pldmtool raw -m 9 -d 0x80 0x00 0x04

# GetSensorReading (Type 2, Command 0x11) for sensor ID 1
pldmtool raw -m 9 -d 0x80 0x02 0x11 0x01 0x00 0x00

Device Integration Examples

NVMe over MCTP

NVMe-MI (Management Interface) uses MCTP for out-of-band management:

# Discover NVMe endpoints
mctp endpoint

# NVMe-MI over MCTP uses message type 0x04
# Query via pldmtool if device supports PLDM
pldmtool base getPLDMTypes -m 11

# For native NVMe-MI, use nvme-cli with MCTP transport
nvme list --mctp

GPU Management

# Configure GPU endpoint (I2C bus 3, address 0x51)
mctp addr add 10 dev mctpi2c3

# Verify endpoint responds
pldmtool base getTID -m 10

# Query GPU sensors
pldmtool platform getSensorReading -m 10 -i 1   # Temperature
pldmtool platform getSensorReading -m 10 -i 2   # Power

# Query GPU capabilities
pldmtool base getPLDMTypes -m 10

PSU Management

# Configure PSU endpoint
mctp addr add 11 dev mctpi2c4

# Read PSU telemetry via PLDM sensors
pldmtool platform getSensorReading -m 11 -i 1   # Input voltage
pldmtool platform getSensorReading -m 11 -i 2   # Output voltage
pldmtool platform getSensorReading -m 11 -i 3   # Output current
pldmtool platform getSensorReading -m 11 -i 4   # Temperature

Host CPU/BIOS Communication

# Host typically at EID 9
# PLDM for BIOS attributes (Type 3)
pldmtool bios GetBIOSTable -m 9 -t StringTable
pldmtool bios GetBIOSTable -m 9 -t AttributeTable
pldmtool bios GetBIOSTable -m 9 -t AttributeValueTable

# Get specific BIOS attribute
pldmtool bios GetBIOSAttributeCurrentValueByHandle -m 9 -a "boot_order"

PLDM Firmware Update

Firmware Update Flow

BMC (Update Agent)                    Device (FD)
      |                                    |
      |  1. QueryDeviceIdentifiers         |
      |------------------------------------>|
      |  <------ Device IDs ---------------|
      |                                    |
      |  2. GetFirmwareParameters          |
      |------------------------------------>|
      |  <------ Component info ------------|
      |                                    |
      |  3. RequestUpdate                  |
      |------------------------------------>|
      |  <------ RequestUpdateResponse -----|
      |                                    |
      |  4. PassComponentTable             |
      |------------------------------------>|
      |  <------ PassComponentTableResp ----|
      |                                    |
      |  5. UpdateComponent (repeat)       |
      |------------------------------------>|
      |                                    |
      |  6. RequestFirmwareData            |
      |<------------------------------------|
      |  ------ Firmware chunk ------------>|
      |     (repeat until complete)        |
      |                                    |
      |  7. TransferComplete               |
      |<------------------------------------|
      |  ------ Acknowledgment ------------>|
      |                                    |
      |  8. VerifyComplete                 |
      |<------------------------------------|
      |  ------ Acknowledgment ------------>|
      |                                    |
      |  9. ApplyComplete                  |
      |<------------------------------------|
      |  ------ Acknowledgment ------------>|
      |                                    |
      |  10. ActivateFirmware              |
      |------------------------------------>|
      |  <------ ActivateResponse ---------|
      |                                    |

Firmware Update Commands

# Query device capabilities
pldmtool fw_update QueryDeviceIdentifiers -m 9
pldmtool fw_update GetFirmwareParameters -m 9

# Start update process
pldmtool fw_update RequestUpdate -m 9 \
    -c 1000 \      # max_transfer_size
    -n 1 \         # number of components
    -m 0 \         # max_outstanding_requests
    -s 1           # package_data_length

# The actual update is typically handled by pldmd
# or a dedicated update agent

Event Handling

PLDM Event Types

Event Class	ID	Description
Sensor Event	0x00	Sensor threshold/state changed
Effecter Event	0x01	Effecter state changed
Redfish Task Executed	0x02	Redfish task complete
Redfish Message	0x03	Redfish log message
PDR Repository Changed	0x04	PDR update
Message Poll	0x05	Async message waiting
Heartbeat	0x06	Keepalive

Sensor Event Format

Sensor Event Data:
+-------+-------+-------+-------+-------+-------+-------+
| Sensor ID (16)        | Sensor Event Class (8)        |
+-----------------------+-------------------------------+
| Event Data (variable based on class)                  |
+-------------------------------------------------------+

Event Monitoring

# Subscribe to PLDM events via D-Bus
busctl monitor xyz.openbmc_project.PLDM

# Poll for platform events
pldmtool platform pollForPlatformEventMessage -m 9

# Check event message buffer size
pldmtool platform getEventMessageBufferSize -m 9

D-Bus Interfaces

MCTP D-Bus Objects

# Service: xyz.openbmc_project.MCTP
# Path: /xyz/openbmc_project/mctp/<network>/<eid>

busctl tree xyz.openbmc_project.MCTP

# Example output:
# └─/xyz/openbmc_project
#   └─/xyz/openbmc_project/mctp
#     └─/xyz/openbmc_project/mctp/1
#       ├─/xyz/openbmc_project/mctp/1/8
#       └─/xyz/openbmc_project/mctp/1/9

# Inspect endpoint
busctl introspect xyz.openbmc_project.MCTP \
    /xyz/openbmc_project/mctp/1/9

# Properties:
#   .Address          - Physical address
#   .NetworkId        - MCTP network ID
#   .EID              - Endpoint ID
#   .SupportedMessageTypes - Supported MCTP message types

PLDM D-Bus Objects

# Service: xyz.openbmc_project.PLDM
# Paths:
#   /xyz/openbmc_project/pldm/terminus/<tid>
#   /xyz/openbmc_project/pldm/fru/<record_set_id>

busctl tree xyz.openbmc_project.PLDM

# Get terminus properties
busctl introspect xyz.openbmc_project.PLDM \
    /xyz/openbmc_project/pldm/terminus/1

# Get sensor value (exposed via standard sensor interface)
busctl get-property xyz.openbmc_project.PLDM \
    /xyz/openbmc_project/sensors/temperature/CPU0_Temp \
    xyz.openbmc_project.Sensor.Value Value

Troubleshooting

MCTP Connectivity Issues

# 1. Check kernel MCTP support
lsmod | grep mctp
modprobe mctp

# 2. Verify I2C bus
i2cdetect -l
i2cdetect -y 1   # Check bus 1

# 3. Check MCTP link status
mctp link
mctp addr

# 4. View mctpd logs
journalctl -u mctpd -f

# 5. Enable debug logging
systemctl edit mctpd
# Add: Environment="MCTP_LOG_LEVEL=debug"
systemctl restart mctpd

# 6. Check MCTP network device
ip link show type mctp
ip -d link show mctpi2c1

PLDM Communication Issues

# 1. Verify endpoint responds
pldmtool base getTID -m 9

# 2. Check PLDM daemon status
systemctl status pldmd

# 3. View PLDM logs
journalctl -u pldmd -f

# 4. Test raw PLDM command
pldmtool raw -m 9 -d 0x80 0x00 0x04  # GetPLDMTypes

# 5. Increase timeout
pldmtool --timeout 30000 base getTID -m 9

No Endpoints Discovered

# 1. Check static configuration
cat /etc/mctp/static-endpoints.json

# 2. Manually add endpoint
mctp addr add 9 dev mctpi2c1

# 3. Verify I2C device responds
i2cdetect -y 1
i2ctransfer -y 1 w1@0x50 0x00

# 4. Check discovery
mctp ctrl discover mctpi2c1

Command Timeouts

# 1. Check endpoint health
mctp stats

# 2. Increase command timeout
pldmtool --timeout 60000 <command>

# 3. Check for I2C bus contention
dmesg | grep -i i2c

# 4. Verify clock speed
# Some devices need slower I2C clock

PDR Issues

# 1. Check PDR repository
pldmtool platform getpdr -t all

# 2. Verify terminus locator
pldmtool platform getpdr -t terminusLocatorPDR

# 3. Check PDR JSON configuration
cat /usr/share/pldm/pdr/*.json

# 4. Rebuild PDR repository
systemctl restart pldmd

Security Considerations

Authentication with SPDM

MCTP/PLDM integrates with SPDM for device authentication:

# SPDM runs over MCTP (message type 0x05)
# See the SPDM Guide for details

# Verify device certificate
# Challenge device
# Establish secure session

Access Control

<!-- /etc/dbus-1/system.d/pldm.conf -->
<!DOCTYPE busconfig PUBLIC
 "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
    <policy user="root">
        <allow own="xyz.openbmc_project.PLDM"/>
        <allow send_destination="xyz.openbmc_project.PLDM"/>
    </policy>
    <policy context="default">
        <allow send_destination="xyz.openbmc_project.PLDM"
               send_interface="org.freedesktop.DBus.Properties"
               send_member="Get"/>
        <allow send_destination="xyz.openbmc_project.PLDM"
               send_interface="org.freedesktop.DBus.Properties"
               send_member="GetAll"/>
    </policy>
</busconfig>

Network Isolation

# MCTP networks are isolated by network ID
# EIDs are only unique within a network

# Use separate networks for different security domains
# Network 1: Host communication
# Network 2: Peripheral devices

Enabling/Disabling

Build-Time Disable

# Remove MCTP/PLDM packages
IMAGE_INSTALL:remove = "mctp mctpd pldm libpldm"

Runtime Disable

# Stop PLDM daemon
systemctl stop pldmd
systemctl disable pldmd

# Stop MCTP daemon
systemctl stop mctpd
systemctl disable mctpd

# Verify stopped
systemctl status pldmd mctpd

Examples

Working examples are available in the examples/mctp-pldm directory:

mctp_health_check.sh - Verify MCTP/PLDM stack connectivity
pldm_discovery.sh - Discover and characterize PLDM endpoints
pldm_sensors.sh - Read numeric and state sensors
pldm_pdr_dump.sh - Dump Platform Descriptor Records
pldm_bios.sh - Read BIOS tables and attributes (Type 3)
pldm_fwupdate.sh - Query firmware update capabilities (Type 5)
config/static-endpoints.json - Static MCTP endpoint configuration
config/pdr.json - PDR repository definition
config/pldm-dbus.conf - D-Bus access policy for PLDM

References

DMTF Specifications

DSP0236 - MCTP Base Specification - Core MCTP protocol
DSP0237 - MCTP SMBus/I2C Transport - I2C binding
DSP0238 - MCTP PCIe VDM Transport - PCIe binding
DSP0239 - MCTP Serial Transport - Serial binding
DSP0240 - PLDM Base Specification - Core PLDM protocol
DSP0248 - PLDM for Platform Monitoring and Control - Type 2
DSP0267 - PLDM for Firmware Update - Type 5

OpenBMC Repositories

libpldm (GitHub) - PLDM library
pldm (GitHub) - PLDM daemon
libmctp (GitHub) - MCTP library
mctp (GitHub) - MCTP userspace tools

Linux Kernel

Linux MCTP Documentation - Kernel MCTP stack

Deep Dive

Advanced implementation details for MCTP/PLDM developers.

MCTP Message Fragmentation

Large PLDM messages are fragmented across multiple MCTP packets:

┌─────────────────────────────────────────────────────────────────────────┐
│                    MCTP Message Fragmentation                           │
├─────────────────────────────────────────────────────────────────────────┤
│                                                                         │
│   PLDM Message (e.g., 500 bytes):                                       │
│   ┌────────────────────────────────────────────────────────────────┐    │
│   │                    PLDM Request/Response Data                  │    │
│   │                         (500 bytes)                            │    │
│   └────────────────────────────────────────────────────────────────┘    │
│                                   │                                     │
│                                   ▼                                     │
│   MCTP Fragmentation (MTU = 64 bytes per binding):                      │
│                                                                         │
│   Packet 1 (SOM=1, EOM=0):                                              │
│   ┌────────┬────────────────────────────────────────────────────────┐   │
│   │ Header │ Data[0:63]                                             │   │
│   │ SOM=1  │                                                        │   │
│   │ EOM=0  │                                                        │   │
│   │ Seq=0  │                                                        │   │
│   └────────┴────────────────────────────────────────────────────────┘   │
│                                                                         │
│   Packet 2 (SOM=0, EOM=0):                                              │
│   ┌────────┬────────────────────────────────────────────────────────┐   │
│   │ Header │ Data[64:127]                                           │   │
│   │ SOM=0  │                                                        │   │
│   │ EOM=0  │                                                        │   │
│   │ Seq=1  │                                                        │   │
│   └────────┴────────────────────────────────────────────────────────┘   │
│                          ...                                            │
│   Packet N (SOM=0, EOM=1):                                              │
│   ┌────────┬────────────────────────────────────────────────────────┐   │
│   │ Header │ Data[remaining]                                        │   │
│   │ SOM=0  │                                                        │   │
│   │ EOM=1  │ ← End of Message                                       │   │
│   │ Seq=7  │                                                        │   │
│   └────────┴────────────────────────────────────────────────────────┘   │
│                                                                         │
│   Header Flags:                                                         │
│   ├── SOM (Start of Message) - First fragment                           │
│   ├── EOM (End of Message) - Last fragment                              │
│   ├── Seq (Sequence) - 2-bit, wraps 0-3                                 │
│   └── Tag - Correlates request/response                                 │
│                                                                         │
└─────────────────────────────────────────────────────────────────────────┘

PLDM Message Type Encoding

┌─────────────────────────────────────────────────────────────────────────┐
│                    PLDM Message Structure                               │
├─────────────────────────────────────────────────────────────────────────┤
│                                                                         │
│   Request Message Format:                                               │
│   ┌────────┬──────────┬──────────┬─────────────────────────────────┐    │
│   │ Byte 0 │  Byte 1  │  Byte 2  │        Bytes 3-N                │    │
│   ├────────┼──────────┼──────────┼─────────────────────────────────┤    │
│   │Instance│   Type   │ Command  │       Request Data              │    │
│   │ ID/Rq  │(0-6 DMTF)│          │                                 │    │
│   └────────┴──────────┴──────────┴─────────────────────────────────┘    │
│                                                                         │
│   Byte 0 breakdown:                                                     │
│   ┌─────┬─────┬──────────────┐                                          │
│   │ D/Rq│ Rsvd│ Instance ID  │                                          │
│   │ 1b  │ 1b  │    5 bits    │                                          │
│   └─────┴─────┴──────────────┘                                          │
│   D=0: Request, D=1: Response                                           │
│   Rq=1: Request message, Rq=0: Response message                         │
│                                                                         │
│   Response Message Format:                                              │
│   ┌────────┬──────────┬──────────┬───────────┬──────────────────┐       │
│   │Instance│   Type   │ Command  │Completion │   Response Data  │       │
│   │ ID/D=1 │          │          │   Code    │                  │       │
│   └────────┴──────────┴──────────┴───────────┴──────────────────┘       │
│                                                                         │
│   PLDM Types:                                                           │
│   ┌──────┬────────────────────────────────────────────────────────┐     │
│   │ Type │ Description                                            │     │
│   ├──────┼────────────────────────────────────────────────────────┤     │
│   │  0   │ PLDM Messaging Control and Discovery                   │     │
│   │  1   │ SMBIOS (not commonly used)                             │     │
│   │  2   │ Platform Monitoring and Control (sensors, PDRs)        │     │
│   │  3   │ BIOS Control and Configuration                         │     │
│   │  4   │ FRU Data                                               │     │
│   │  5   │ Firmware Update                                        │     │
│   │  6   │ Redfish Device Enablement                              │     │
│   └──────┴────────────────────────────────────────────────────────┘     │
│                                                                         │
└─────────────────────────────────────────────────────────────────────────┘

PDR (Platform Descriptor Record) Database

┌─────────────────────────────────────────────────────────────────────────┐
│                    PDR Repository Structure                             │
├─────────────────────────────────────────────────────────────────────────┤
│                                                                         │
│   PDR Repository (stored in pldmd):                                     │
│   ┌─────────────────────────────────────────────────────────────────┐   │
│   │ Record │ Type                    │ Description                  │   │
│   ├────────┼─────────────────────────┼──────────────────────────────┤   │
│   │   1    │ Terminus Locator (11)   │ BMC terminus info            │   │
│   │   2    │ Numeric Sensor (2)      │ CPU temperature              │   │
│   │   3    │ Numeric Sensor (2)      │ DIMM temperature             │   │
│   │   4    │ Numeric Sensor (2)      │ Fan speed                    │   │
│   │   5    │ Numeric Effecter (9)    │ Fan PWM control              │   │
│   │   6    │ State Sensor (4)        │ Presence sensor              │   │
│   │   7    │ FRU Record Set (20)     │ System FRU data              │   │
│   │   ...  │ ...                     │ ...                          │   │
│   └─────────────────────────────────────────────────────────────────┘   │
│                                                                         │
│   PDR Record Common Header:                                             │
│   ┌──────────┬────────────┬───────────┬────────────┬────────────────┐   │
│   │Record Hdl│ PDR Header │Record Type│ Data Length│   Record Data  │   │
│   │ (4 bytes)│  Version   │ (1 byte)  │  (2 bytes) │   (variable)   │   │
│   └──────────┴────────────┴───────────┴────────────┴────────────────┘   │
│                                                                         │
│   Numeric Sensor PDR (Type 2) key fields:                               │
│   ├── Sensor ID (2 bytes)                                               │
│   ├── Entity Type (CPU, Memory, Fan, PSU, etc.)                         │
│   ├── Entity Instance                                                   │
│   ├── Sensor Init (thresholds, hysteresis)                              │
│   ├── Unit (Degrees C, RPM, Volts, Amps, Watts)                         │
│   ├── Resolution, Offset, Accuracy                                      │
│   └── Threshold values (warning, critical, fatal)                       │
│                                                                         │
│   JSON PDR Configuration (pldm/pdr_jsons/):                             │
│   {                                                                     │
│       "pdrType": 2,                                                     │
│       "sensorID": 1,                                                    │
│       "entityType": 66,  // Processor                                   │
│       "baseUnit": 2,     // Degrees C                                   │
│       "warningHigh": 85.0,                                              │
│       "criticalHigh": 95.0                                              │
│   }                                                                     │
│                                                                         │
└─────────────────────────────────────────────────────────────────────────┘

Endpoint Discovery Flow

┌─────────────────────────────────────────────────────────────────────────┐
│                    MCTP Endpoint Discovery                              │
├─────────────────────────────────────────────────────────────────────────┤
│                                                                         │
│   BMC                                    Remote Endpoint                │
│    │                                           │                        │
│    │  1. MCTP Control: Get Endpoint ID         │                        │
│    │──────────────────────────────────────────▶│                        │
│    │◀──────────────────────────────────────────│ EID assigned: 0x08     │
│    │                                           │                        │
│    │  2. MCTP Control: Get Message Types       │                        │
│    │──────────────────────────────────────────▶│                        │
│    │◀──────────────────────────────────────────│ [PLDM, VDM]            │
│    │                                           │                        │
│    │  3. PLDM Type 0: GetTID                   │                        │
│    │──────────────────────────────────────────▶│                        │
│    │◀──────────────────────────────────────────│ TID: 1                 │
│    │                                           │                        │
│    │  4. PLDM Type 0: GetPLDMTypes             │                        │
│    │──────────────────────────────────────────▶│                        │
│    │◀──────────────────────────────────────────│ [Type 0, 2, 5]         │
│    │                                           │                        │
│    │  5. PLDM Type 0: GetPLDMCommands (Type 2) │                        │
│    │──────────────────────────────────────────▶│                        │
│    │◀──────────────────────────────────────────│ [cmd list for Type 2]  │
│    │                                           │                        │
│    │  6. PLDM Type 2: GetPDRRepositoryInfo     │                        │
│    │──────────────────────────────────────────▶│                        │
│    │◀──────────────────────────────────────────│ RepoSize, RecordCount  │
│    │                                           │                        │
│    │  7. PLDM Type 2: GetPDR (loop)            │                        │
│    │──────────────────────────────────────────▶│                        │
│    │◀──────────────────────────────────────────│ PDR records...         │
│    │                                           │                        │
│                                                                         │
│   After discovery, pldmd creates D-Bus objects for each PDR:            │
│   /xyz/openbmc_project/pldm/fru/...                                     │
│   /xyz/openbmc_project/sensors/temperature/PLDM_Sensor_...              │
│                                                                         │
└─────────────────────────────────────────────────────────────────────────┘

Source Code Reference

Key implementation files:

Repository	File	Description
libpldm	`src/base.c`	Base message encode/decode
libpldm	`src/platform.c`	Type 2 (Platform) messages
libpldm	`src/fru.c`	Type 4 (FRU) messages
libpldm	`src/fw_update.c`	Type 5 (Firmware Update)
pldm	`pldmd/pldmd.cpp`	Main PLDM daemon
pldm	`libpldmresponder/`	Response handlers
pldm	`requester/`	Request handlers
mctp	`src/mctp.c`	MCTP transport layer

Tested on: OpenBMC master, requires hardware with MCTP-capable endpoints. QEMU testing possible with mctp-serial loopback.

MCTP & PLDM Guide

Table of Contents

Overview

Why MCTP/PLDM?

Protocol Stack

MCTP Protocol Deep Dive

MCTP Packet Format

Header Fields

Special Endpoint IDs

MCTP Message Types

MCTP Control Messages

Control Commands

Message Fragmentation

MTU by Transport

MCTP Transport Bindings

I2C/SMBus Binding (DSP0237)

I2C Configuration

Device Tree for I2C MCTP

PCIe VDM Binding (DSP0238)

PCIe VDM Configuration

Serial Binding (DSP0239)

PLDM Protocol Deep Dive

PLDM Message Format

Header Fields

PLDM Types

PLDM Type 0: Base Commands

Example: Get TID

PLDM Type 2: Monitoring & Control

Sensor Commands

Effecter Commands

Event Commands

PLDM Type 5: Firmware Update

Platform Data Records (PDR)

PDR Structure

PDR Types

Numeric Sensor PDR Example

State Sets

Querying PDRs

OpenBMC Implementation

Architecture

libmctp

libpldm

pldmd Configuration

Setup & Configuration

Build-Time Configuration (Yocto)

Meson Build Options (pldm)

Meson Build Options (mctpd)

Kernel Configuration

Runtime Configuration

MCTP Configuration

Managing MCTP Networks

Endpoint Management

Static Endpoint Configuration

D-Bus Interface for MCTP

PLDM Configuration

PDR Repository

Common PLDM Commands

Raw PLDM Commands

Device Integration Examples

NVMe over MCTP

GPU Management

PSU Management

Host CPU/BIOS Communication

PLDM Firmware Update

Firmware Update Flow

Firmware Update Commands

Event Handling

PLDM Event Types

Sensor Event Format

Event Monitoring

D-Bus Interfaces

MCTP D-Bus Objects

PLDM D-Bus Objects

Troubleshooting

MCTP Connectivity Issues

PLDM Communication Issues

No Endpoints Discovered

Command Timeouts

PDR Issues

Security Considerations