Chapter 2 of 3 · Specification to Microarchitecture

Assign state ownership and boundary contracts

Partition decisions and mutable state into precise owners, then define acceptance, lifetime, ordering, backpressure, error, reset, and cancellation at every interface.

Inspect interface contracts Practice questions

Partition by ownership

Place state where one block can make it precise.

Partitioning is not drawing boxes around functions. It assigns every mutation, wait, retry, and completion to one owner while controlling shared critical paths.

CH0descriptorepochprogress

CH1descriptorepochprogress

CH2descriptorepochprogress

CH3descriptorepochprogress

eligibilityScheduler + credit gateBurst formationResponse ledger

256-bit downstream boundaryacceptance · ordering · error · backpressure

Block ownership ledger
State	Allocate	Mutate	Retire	Observable evidence
Descriptor context	Channel front	Channel front	Channel front	accepted / active / completed counters
Fabric credit	Response ledger	Issue + response	Response ledger	outstanding high-water mark
Burst progress	Burst engine	Burst engine	Response ledger	channel, descriptor, burst, beat identity
First error	Response ledger	write-once until retire	Channel front	cause, address, bytes committed, epoch

Interface and state contracts

Define acceptance, lifetime, and cancellation together.

Signal direction is not an interface contract. Every boundary also needs a sampling event, stability rule, ownership transfer, ordering scope, error semantics, and reset behavior.

Admission

Descriptor request

Accept: req_valid && req_ready
Stable while blocked: address, length, channel, flags
Transfer: caller → channel front
Reject: alignment, range, or disabled channel

Transport

Fabric beat

Accept: valid && ready at the fabric edge
Stable while blocked: payload, byte enables, ID, LAST
Order: as defined for the selected ID and channel
Capacity: one credit per accepted outstanding unit

Retirement

Channel completion

Emit: after every accepted burst reaches terminal state
Report: status, bytes committed, first error
Reuse: only after completion acceptance
Reset: drain, cancel, or reject by declared epoch

Conservation invariantaccepted descriptors = completed descriptors + active descriptors

Refine the same conservation equation for bursts, beats, credits, and response IDs. After quiescence, every active count must reach zero.

Put it into practice

Explain the decision behind the design.

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