# DMAC Contract

Status: `Draft`

## Purpose

Define the EE DMA controller as a first-class subsystem with explicit channel
behavior and traceability.

## Owns

- channel register state,
- channel start/stop logic,
- priority / scheduling policy,
- interrupt generation,
- transfer-side coordination to VIF, GIF, SIF, IPU, and scratchpad-related
  endpoints.

## EE channels in scope

- ch0 VIF0
- ch1 VIF1
- ch2 GIF
- ch3 IPU_FROM
- ch4 IPU_TO
- ch5 SIF0
- ch6 SIF1
- ch7 SIF2
- ch8 SPR_FROM
- ch9 SPR_TO

## Inputs

- CPU writes to DMAC registers,
- memory responses,
- endpoint ready/busy signals,
- reset/interrupt masking controls.

## Outputs

- memory read/write traffic,
- endpoint transfers,
- stall/busy signals,
- interrupt status updates,
- channel-level trace events.

## Questions to lock

- What is the minimum channel set for first visible output?
- How much of stall/ring behavior is required before BIOS or homebrew becomes
  meaningful?
- Will the internal datapath be modeled around 128-bit transfers from day one?

## Allowed early stubs

- channel register file with no data movement,
- one-channel functional path for GIF-first testing,
- simplified arbitration before full priority behavior.

## Required debug visibility

- per-channel start/stop,
- source/destination context,
- transfer counts,
- interrupts,
- blocked-on-endpoint reasons.

## First meaningful milestone

- ch2 GIF path can move a known-good packet stream from memory into a GS/GIF
  test endpoint while producing deterministic traces.