MIPS overlay code Inferred
Static disc copies of runtime overlays - small subsystem code blobs that load into the 0x801C0000+ overlay window. Distinct from the major full-scene overlays (title / town / battle / options); these are smaller specialised blobs from the 0901..=0969_xxx_dat PROT range.
Overview
Implementation: crates/asset/src/mips_overlay.rs.
Layout
+0x00 u32 0x27BDFFXX ; addiu sp, sp, -X (negative stack adjust)
+0x04 u32 prologue follow-up; sw ra/s* (0xAFB?_00XX), or another addiu /
; lui / sw / R-type - the second instruction
; of the entry function's prologue
+0x08 ... ; rest of the overlay code blobDetection
Three checks together produce zero false positives across the corpus:
u32_le[0] & 0xFFFF_FF00 == 0x27BD_FF00-addiu sp, sp, -X.(u32_le[0] & 0xFF) ∈ [0x80, 0xF8]- only accept reasonable stack adjustments (8 to 128 bytes).u32_le[1]'s 6-bit MIPS opcode field is one of the common function-prologue follow-ups (sw,addiu,lui,lw, R-type, ldc/sdc).
Cluster anatomy
All matches cluster in the 0901..=0969 PROT range - sized 14 KB to 37 KB (one outlier at 163 KB for 0969_xxx_dat.BIN). The find-overlay heuristic ranks these as MIPS-code-shape candidates; this detector formalises that ranking into the categorize pipeline.
Each entry can be Ghidra-imported via scripts/bulk-import-overlays.sh once a base address is determined. The overlay window is 0x801C0000–0x80200000; each blob loads at a specific offset within that range, determinable from the asset chain that pulls it in.
Likely subsystems
Based on size and the xxx_dat clustering: cutscenes, world-map, menu screens, mini-games, or per-scene specialised code that doesn't fit in the main town-field overlay.
Reading the format
use legaia_asset::mips_overlay;
if let Some(m) = mips_overlay::detect(buf) {
println!("MIPS overlay: stack frame = {} bytes; second op = {:#04x}",
m.stack_frame_bytes, m.second_op);
}