ADR 0061: Bundle commit state uses BARG/BPCN

• Date: 2026-08-11
• Requirements: PTO-REQ-BUNDLE-STATE-001, PTO-REQ-BUNDLE-DISPATCH-001, PTO-REQ-BUNDLE-OPERATION-001

Context

The PTO block-lifecycle model carries a candidate target and a sequential continuation but does not yet expose them through one complete architectural bundle-argument record. The formal contract requires one current block address, one candidate next block address, an explicit transfer kind, and an explicit taken decision without creating duplicate target or trap fields.

Decision

BARG.BPC is a 64-bit field containing the current BSTART address. Hardware sets it when the block is initialized.

BARG.BPCN is a 64-bit field containing the candidate next block-head address. SETC.TGT and C.SETC.TGT write this field. TGT and BPC.TGT are alternate names for this same architectural value; they MUST NOT create a second target field.

BPCN, TYPE, and TAKEN are valid only for STD and FP blocks. SYS blocks have BPC and BlockType, plus their applicable ordering attributes, but do not have these three block-transfer fields. PTO reserves no second meaning for the physical BPCN storage.

BARG.TYPE records the block-transfer kind and BARG.TAKEN records whether the candidate target is selected. At block commit:

• FALL and a false COND continue at the sequential next BSTART;
• STD/FP DIRECT, CALL, IND, ICALL, RET, and a true COND continue at BARG.BPCN;
• the selected continuation becomes the next block PC only after successful block commit.

Direct, call, indirect, indirect-call, and return forms initialize TAKEN=1. FALL initializes TAKEN=0. Conditional forms initialize or update TAKEN from their condition operation while retaining their encoded target in BPCN.

BARG has no architectural TRAP field. Trap and exception state are handled by the separate PTO trap/context model.

BSTOP, C.BSTOP, L.BSTOP, and a following BSTART are commit boundaries. They MUST read the same BARG record, choose the continuation as above, commit the current block atomically, and clear the retiring block's BARG and private state after successful commit. A final block MUST end with a BSTOP form.

Consequences

• PTO MUST replace parallel target explanations with one BARG/BPCN architectural definition while retaining an internal sequential continuation value where needed to model a false condition.
• The current _BundleTarget state maps to BARG.BPCN; it is not an independent architectural field.
• The current _BundleFallthrough value is implementation support for the sequential continuation; it is not BPCN.
• PTO legality must reject transfer forms on block types for which BARG does not provide BPCN, TYPE, and TAKEN.
• PTO ASL, instruction pages, AVS points, trap-context projection, and release evidence MUST use the same names, widths, initialization, selection, commit, and clearing rules.

Evidence

• asl/block/model/state/control-state.asl
• asl/block/model/lifecycle/begin.asl
• asl/block/model/lifecycle/enter-stop.asl
• asl/block/lifecycle/BSTART.asl
• asl/block/lifecycle/BSTOP.asl
• asl/block/lifecycle/C.BSTOP.asl
• asl/block/lifecycle/L.BSTOP.asl