thejayman77
ec82764bef
RTL (GS rasterizer, EE core stub, platform bridge, LPDDR4B path), sim regression (272 TBs), docs, and tooling. Copyrighted PS2 content (BIOS, game code, GS dumps, and all dump-derived textures/traces) is excluded via .gitignore and stays local. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
81 lines
3.1 KiB
Systemverilog
81 lines
3.1 KiB
Systemverilog
// retroDE_ps2 — clut_stub (Ch97)
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//
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// Minimal palette RAM for indexed-color scanout. PSMT8 scanout
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// (Ch96) currently surfaces the index as grayscale; with this
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// CLUT wired in, the index is looked up to produce real RGB.
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//
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// Scope (intentionally minimal for Ch97):
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// - 256 entries × 32 bits (PSMCT32 ABGR per entry). PSMT4
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// (16 entries) uses the same RAM with a smaller index range.
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// - CSM2 (linear) addressing only. Index N reads entry N. CSA
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// (entry offset) is honored OUTSIDE this module — pcrtc
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// computes effective_idx = idx + (CSA << 4) and presents it
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// as `read_idx`. CSM1 (16×16 grid swizzle inside a CSPM
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// block) is deferred.
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// - Combinational read port for pcrtc (tight scanout latency).
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// - Single registered write port. Two writers exist at this
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// scope, picked by the wiring at the TB level:
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// (a) TB-direct programming for tests that want to lock
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// pcrtc-side decode in isolation (Ch97 PSMT8+CLUT TB,
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// Ch98 TEX0_1 CSA-flow TB).
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// (b) `clut_loader_stub` (Ch99/Ch100) — a small FSM that
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// copies 256 entries from VRAM[CBP*256] into this RAM
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// when a TEX0_1 GIF write commits with CLD!=0,
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// CSM=CSM2, and CPSM ∈ {PSMCT32, PSMCT16}. PSMCT16
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// entries are unpacked from RGB5A1 to PSMCT32 ABGR
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// inside the loader, so clut_stub always stores
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// PSMCT32 regardless of source. clut_stub doesn't know
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// which writer is in play; it just commits whatever
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// the wired write_* port carries.
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//
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// Real PS2 CLUT is held in a 1 KiB internal staging area and
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// loaded from VRAM[CBP] when CLD bits in TEX0 fire. Ch99/Ch100
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// model the load path for CPSM ∈ {PSMCT32, PSMCT16} with CSM2;
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// CSM1 swizzle, conditional CLD modes (2..7), CSA partial-window
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// loads (CLD=4), and CPSM ∉ {PSMCT32, PSMCT16} stay deferred.
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`timescale 1ns/1ps
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module clut_stub
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#(
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parameter int unsigned ENTRIES = 256
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) (
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input logic clk,
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input logic rst_n,
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// TB-direct write port (no GIF TEX0 path yet).
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input logic write_en,
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input logic [7:0] write_idx,
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input logic [31:0] write_data,
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// Combinational read port consumed by gs_pcrtc_stub (scanout).
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input logic [7:0] read_idx,
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output logic [31:0] read_data,
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// Ch296 — SECOND combinational read port for the TEXTURE sampler
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// (gs_stub texel-fetch path). Independent of the pcrtc scanout port
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// above: the table is a tiny 256x32 LUT, so a second read fan-out is
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// free and keeps the two consumers (scanout vs sampler) decoupled.
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// PSMT8 indexed texturing looks up clut_stub[tex_read_idx] to turn a
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// fetched 8-bit index into a PSMCT32 color.
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input logic [7:0] tex_read_idx,
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output logic [31:0] tex_read_data
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);
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logic [31:0] mem [0:ENTRIES-1];
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initial begin
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for (int i = 0; i < ENTRIES; i++) mem[i] = 32'd0;
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end
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assign read_data = mem[read_idx];
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assign tex_read_data = mem[tex_read_idx];
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always_ff @(posedge clk) begin
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if (rst_n && write_en) begin
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mem[write_idx] <= write_data;
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end
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end
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endmodule : clut_stub
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