D754 - An unwritten index size is sixteen bits

Status: decided Date: 2026-10-07

An indexed draw whose stream, and every submission carried into it (D737), never wrote VGT_INDEX_TYPE reads sixteen-bit indices (INDEX_TYPE 0, VGT_INDEX_16). A size the stream did write is read as written, and the eight-bit size is still refused. This narrows D740, which refused an unwritten size. It is assumed, so a hardware row showing another reset value retires it.

Why: PPSA28061 draws with DRAW_INDEX_OFFSET_2 after sceAgcDcbSetIndexBuffer and sceAgcDcbSetIndexCount, and imports no sceAgcDcbSetIndexSize. The measured SetIndexBuffer emits only INDEX_BASE (166-agc/dcb-set-index-buffer). Nothing in its submissions writes the register, directly or by an indirect uconfig load. The six indices it binds read 0, 1, 2, 0, 2, 3 as sixteen-bit values: one quad. As thirty-two-bit values they would be 0x10000, 2, 0x30002, 0, 0, 0, which no six-index draw names. So the size in force on hardware is sixteen bits, and refusing the draw only hides that.

Rejected:

• Keeping D740's refusal. It holds every draw of a title that relies on the queue's size.
• Inferring the size per draw from the index data. A guess from data is a per-title heuristic, and a thirty-two-bit buffer of small indices reads as plausible sixteen-bit ones.