ADR 0054: PE-Local Tile Size and 32-bit Shared I/O Binding

Inventory counts in this record are acceptance-time historical context; the current inventory is owned by the ASL tree and its generated projections.

• Date: 2026-08-06
• Deciders: PTO ISA maintainers

Current release inventory is governed by ASL and generated projections; numeric inventories below are acceptance-time history, not the current active decoder set.

Context

PTO ISA 0.58 originally described TSize using a four-PE aggregate size table even though Tile dimensions and execution are programmed at PE granularity. That mixed two architectural levels: encoded dimensions described one PE while encoded capacity described the Core aggregate.

The active 16-bit C.B.IOS binder also carried only an absolute SharedTID. GM-to-Shared TLOAD therefore reinterpreted B.IOR.RegDst[11:9] as a Shared size, and Shared TLSU operations used a destination-free B.IOT as a mask-only companion. That B.IOT spelling is binary-identical to an existing Local T destination form and cannot round-trip unambiguously. Local-to-Shared TMOV additionally borrowed the Local binder's destination-size field for a Shared destination.

Decision

PTO ISA 0.58 is reissued in place. The architecture version remains 0.58.0 and the existing ABI string remains unchanged; the regenerated release manifest and content hashes identify the replacement specification tree. Artifacts built against the superseded 0.58 tree are stale and must not be mixed with the reissued toolchain.

B.DIM dimensions and every explicit Tile destination TSize describe one selected PE. The nonzero size table is 128 B, 256 B, 512 B, 1 KiB, 2 KiB, 4 KiB, and 8 KiB for codes 1 through 7. Core allocation is popcount(PE_MASK) * per_pe_size. Mask bits map to fixed identities: 1000=PE0, 0100=PE1, 0010=PE2, and 0001=PE3; selected PEs are never packed. Mask zero is a strict no-op with no allocation, rename, source read, memory access, state change, binder consumption, lifetime transition, or fault.

The active Shared operand binder is replaced by 32-bit B.IOS:

width       = 32
opcode      = 0x13
funct3      = 001
match       = 0x00001013
mask        = 0xf00871ff
SharedTID   = bits[27:20]
PE_MASK     = bits[18:15]
TSize       = bits[11:9]
reserved    = bits[31:28], bit[19], bits[8:7] (all zero)

It belongs to catalog semantic group Bundle Input & Output and uses handler BindBundleSharedIO. TSize=0 denotes a Shared source; TSize=1..7 denotes a Shared destination and declares per-PE capacity. The encoded role must agree with the selected operation schema. One instruction binds one absolute Core-private register S0..S255; at most four ordered bindings may be live. Duplicate unconsumed IDs and a fifth binding are illegal.

B.IOS owns Shared ID, role/size, and PE mask. B.IOR owns scalar/address operands only and RegDst is zero in Shared TLSU schemas. B.IOT owns Local Tile operands only and has no mask-only Shared form. Mixed Local/Shared operations require equal masks. Shared CUBE operands are sources with TSize=0 and mask 1111; TGEMV rejects every Shared binder.

The first nonzero allocating Shared write records an immutable allocation mask and one per-PE descriptor. Later destination writes may update a subset but may not expand the allocation mask; the compiler allocates a new Sx for a different mask or incompatible descriptor. Reads of unallocated or uninitialized Shared lanes retain undefined-register behavior: no trap and no state change. Shared destination updates remain atomic descriptor-plus-selected- payload operations. The architecture imposes no ordering on conflicting PE accesses; programs must avoid conflicts.

For MShard4, encoded M, N, and K remain per-PE and the group view derives group_M=4*pe_M, group_N=pe_N, and group_K=pe_K. Other distribution kinds must define their own derivation.

Consequences

• The C.B.IOS mnemonic and form are removed from the active catalog and rejected by the assembler. Its historical raw bit pattern decodes only as the overlapping active C.B.DIMI form; active B.IOS is added, so the command-form count remains 99.
• The reviewed 573-form binary envelope is rebound to SHA-256 fingerprint 9155a78499c4908e0fdc7ac2a48159eacb5c1dfc78ea724dbedf689369430993.
• The old reviewed C.B.DIMI/C.B.IOS catalog-overlap exception is removed because only C.B.DIMI remains active at that bit pattern.
• BundleSharedBinding gains size_code and pe_mask, including reset, consume, trap snapshot, and recovery behavior.
• GM-to-Shared TLOAD size and mask come from B.IOS; Shared stores use source B.IOS; Local-to-Shared TMOV takes Shared capacity from destination B.IOS; Shared-to-Local keeps Local capacity in destination B.IOT.
• All legality checks occur before memory, payload, descriptor, allocation, rename, destination finalization, or binder consumption effects.
• Catalogs, ASL, tests, requirements, Markdown, HTML, XLSX, evidence, release manifest, and downstream PTO consumers must be regenerated.

Supersession

ADR 0045's B.IOT allocation-size-code paragraph and ADR 0052's aggregate Tile-size table remain historical. This ADR supersedes those size encodings, plus ADR 0052's active C.B.IOS encoding, B.IOR Shared-size carrier, mask-only B.IOT companion, and Shared binder schema. The retained operation inventory and extension-encoding reservations in ADR 0052 remain in force.

This ADR also supersedes ADR 0052's current Tile/Bundle assertion-inventory pin. The direct assertions protecting a valid live B.IOS binding and a nonzero first-allocation mask raise that fail-closed inventory from 200 to 202; the scalar/system/concurrency inventory remains 34.

Rejected Alternatives

• Keeping aggregate sizes leaves dimensions and capacity at different levels.
• Reusing B.IOR.RegDst keeps Tile allocation metadata in a scalar binder.
• A destination-free B.IOT is ambiguous with an existing Local T destination.
• Extending C.B.IOS cannot fit the approved ID, size, and mask contract.
• A separate direction bit is unnecessary because zero/nonzero TSize already distinguishes source and destination roles.
• Keeping both binders active creates two 0.58 ABIs and violates the approved clean break.
• A new 0.59 release or ABI-v2 suffix is not used; this decision replaces the earlier 0.58 design before toolchain stabilization.