pmbus

Documentation

Overview

Package pmbus decodes PMBus — the Power Management Bus, an SMBus/I2C command set (PMBus spec) that PSUs, voltage regulators (VRMs), battery chargers and hot-swap controllers expose to set and read their power rails. PMBus is a real and current hardware-attack surface: the 2023 "PMFault" research showed that writing the PSU's VOUT_COMMAND / OPERATION over PMBus can overvolt a server's CPU rail to induce faults — so a captured PMBus transaction (from an I2C/SMBus sniffer, cf. the project's i2c_scan) is real recon. A PMBus message identifies the **command** in flight — a voltage-setting OPERATION / VOUT_COMMAND / VOUT_MARGIN (the attack-relevant writes, flagged), a READ_VIN / READ_VOUT / READ_IOUT / READ_TEMPERATURE telemetry read, a STATUS query, a manufacturer-ID query — and, for the LINEAR11 telemetry reads, the decoded physical value. It joins the project's hardware-bus tooling (internal/jtag, internal/buspirate, internal/spiflash).

Wrap-vs-native judgement

Native. A PMBus transaction is a 1-byte command code optionally followed
by little-endian data; telemetry values use the LINEAR11 (5-bit signed
exponent + 11-bit signed mantissa) float encoding and STATUS words are
bit-fields. A byte read + an opcode table + a couple of bit/float decodes;
stdlib only, no new go.mod dep.

Verifiable / no confidently-wrong output

The decoded command codes are the PMBus-specification standard set
(OPERATION, VOUT_COMMAND, the VOUT margins/limits, the READ_* telemetry,
the STATUS_* registers, PMBUS_REVISION, MFR_ID, …); a code outside the set
is reported as unknown / manufacturer-specific rather than guessed. The
LINEAR11 decode (deterministic two's-complement exponent × mantissa) is
applied only to the commands defined as LINEAR11 (the current / power /
temperature / input-voltage reads); VOUT-format values (ULINEAR16, scaled
by the device's VOUT_MODE exponent which is not on the wire) are surfaced
raw with a note, and STATUS bit-fields are decoded from the spec. Other
command data is surfaced as raw hex.

Index

• type Result
  • func Decode(input string) (*Result, error)

Types

type Result

type Result struct {
	Command     int    `json:"command"`
	CommandHex  string `json:"command_hex"`
	CommandName string `json:"command_name"`

	Value             string   `json:"value,omitempty"`
	StatusFlags       []string `json:"status_flags,omitempty"`
	SecurityRelevance string   `json:"security_relevance,omitempty"`

	DataHex string   `json:"data_hex,omitempty"`
	Notes   []string `json:"notes,omitempty"`
}

Result is the decoded view of a PMBus transaction.

func Decode

func Decode(input string) (*Result, error)

Decode parses a PMBus transaction (command code + little-endian data) from hex (whitespace / ':' / '-' / '_' separators and a '0x' prefix tolerated).