// retroDE_ps2 — tb_top_psmct32_sh3_multitex  (Ch355 Brick 1 — MULTI-TEXTURE composition)
//
// Two authentic SH3 draws with DIFFERENT TEX0/CLUT accumulate into ONE LPDDR framebuffer via scene-level texture
// rebind + staged-list retriggering. Dump order: A=idx19562 (tbp=11264/CBP_A) THEN B=idx89761 (tbp=9216/CBP_B).
// Proves Codex's Ch355 gates:
//   * TWO cache fills, each fill_done low->high, expected beats/bytes, 0 read errors, texture-specific CRC (A then B).
//   * NO stale-frame_drained race: EACH scene requires an observed frame_drained high->low->high (not a lingering 1).
//   * preclear EXACTLY once; scanout stays disabled until the SECOND fresh drain.
//   * records_emitted per list; final FB scored vs the independent A->B reference; OVERLAP scored separately.
//   * FB 320x381 (FBW=5), stride 1280, scanout 15240 beats/frame.
// LOCAL/gitignored fixtures; skip-guard if absent.
`timescale 1ns/1ps

module tb_top_psmct32_sh3_multitex;
`include "sh3_mt_params.vh"                     // FBPXW=320, FBH=381, CBP_A/CBP_B, NTRIS_A/B, CRC_TEX_A/B, ...
    localparam int W = FBPXW, H = FBH;
    localparam int STRIDE = W*4;                // 1280
    localparam int ROW_BEATS = STRIDE/32;       // 40
    localparam int FB_BYTES = STRIDE*H;         // 487680
    localparam int FB_WORDS = W*H;
    localparam int BEATS_PER_FRAME = ROW_BEATS*H;   // 15240
    localparam int H_ACT=W, V_ACT=H, H_BP=32, H_FP=8, V_BP=16, V_FP=8;
    localparam int H_TOT=H_BP+H_ACT+H_FP, V_TOT=V_BP+V_ACT+V_FP;

    logic clk=0;       always #5 clk=~clk;
    logic emif_clk=0;  always #2 emif_clk=~emif_clk;
    logic video_clk=0; always #7 video_clk=~video_clk;
    logic rst_n; logic fb_commit=0; always #13 fb_commit=~fb_commit;
    int errors; initial errors=0;

    // ===== bram-top (FB_LPDDR_ONLY, AUTOSTART off, STG 2048), H/V_ACTIVE = 320x381 =====
    logic        core_go; logic [7:0] r,g,b; logic hsync,vsync_o,de;
    logic        core_halt,dma_done_seen,frame_seen,raster_overflow,frame_toggle,dma_done_toggle;
    logic        feeder_go_tb, feeder_ready_tb; logic [15:0] feeder_records_w; logic [31:0] feeder_waits_w;
    logic        gs_tex_rd_en_o; logic [31:0] gs_tex_rd_addr_o; logic [31:0] tex_cache_data; logic tex_cache_ready;
    logic [31:0] tex_cache_hits, tex_bram_hits;
    logic        flush_emit_w; logic [31:0] flush_addr_w; logic [31:0] flush_color32_w; logic [5:0] flush_psm_w;

    top_psmct32_raster_demo_bram #(
        .H_ACTIVE(FBPXW), .V_ACTIVE(FBH),
        .VRAM_BYTES(VRAM_BYTES_P), .VRAM_ENABLE_READ2(1'b0), .PSMCT32_SWIZZLE(1'b0),
        .COMBINED_TAZ(1'b0), .TILE_LOCAL(1'b0), .TILE_COLS(1), .TILE_ROWS(1),
        .TILE_MULTIPRIM(1'b0), .TILE_PRIM_COUNT(1), .TILE_FIFO_DEPTH(8),
        .BIN_BUFFER_ENABLE(1'b0), .HEARTBEAT_SPLICE_ENABLE(1'b0),
        .FEEDER_ENABLE(1'b1), .FEEDER_STG_WORDS(STG_WORDS), .FEEDER_AUTOSTART(1'b0),
        .PERSPECTIVE_CORRECT(1'b1), .PERSP_RECIP_IDX_BITS(11),
        .GRAD_SEQ_DIVIDER(1'b1), .GRAD_DIV_CYCLES(4),
        .GS_LPDDR_TEX(1'b1), .TEX_VRAM_BASE(TEX_VRAM_BASE), .TEX_CACHE_BYTES(TEX_BYTES),
        .CLUT_CSM1_ENABLE(1'b1), .FB_LPDDR_ONLY(1'b1)
    ) dut (
        .clk(clk), .rst_n(rst_n), .core_go(core_go),
        .r(r), .g(g), .b(b), .hsync(hsync), .vsync(vsync_o), .de(de),
        .core_halt(core_halt), .dma_done_seen(dma_done_seen), .frame_seen(frame_seen), .raster_overflow(raster_overflow),
        .frame_toggle(frame_toggle), .dma_done_toggle(dma_done_toggle), .joy_a_pressed_i(1'b0), .joy_b_pressed_i(1'b0),
        .feeder_stg_we_i(1'b0), .feeder_stg_waddr_i(12'd0), .feeder_stg_wdata_i(64'd0),
        .feeder_go_i(feeder_go_tb), .feeder_ready_o(feeder_ready_tb),
        .feeder_records_o(feeder_records_w), .feeder_waits_o(feeder_waits_w),
        .flush_emit_o(flush_emit_w), .flush_addr_o(flush_addr_w),
        .flush_pix16_o(), .flush_color32_o(flush_color32_w), .flush_psm_o(flush_psm_w),
        .gs_tex_rd_en_o(gs_tex_rd_en_o), .gs_tex_rd_addr_o(gs_tex_rd_addr_o),
        .tex_cache_data_i(tex_cache_data), .tex_cache_ready_i(tex_cache_ready),
        .tex_cache_hits_o(tex_cache_hits), .tex_bram_hits_o(tex_bram_hits)
    );

    // texture cache + behavioral texture LPDDR (RELOADED between fills for the rebind)
    logic [29:0] araddr; logic [1:0] arburst; logic [6:0] arid; logic [7:0] arlen; logic [2:0] arsize;
    logic        arvalid, arready; logic [255:0] rdata; logic [1:0] rresp; logic rlast, rvalid, rready;
    logic        fill_start, fill_done; logic [31:0] fill_beats, fill_bytes, tex_rd_errs, fill_crc_w;
    gs_texture_cache #(.LPDDR_TEX_BASE(LPDDR_TEX_BASE), .TEX_VRAM_BASE(TEX_VRAM_BASE),
                       .TEX_BYTES(TEX_BYTES), .N_BEATS(N_BEATS)) u_cache (
        .axi_clk(clk), .axi_rst_n(rst_n), .fill_start(fill_start), .fill_done(fill_done),
        .fill_beats(fill_beats), .fill_bytes(fill_bytes), .rd_errs(tex_rd_errs), .fill_crc(fill_crc_w),
        .araddr(araddr), .arburst(arburst), .arid(arid), .arlen(arlen), .arsize(arsize), .arvalid(arvalid), .arready(arready),
        .rdata(rdata), .rresp(rresp), .rlast(rlast), .rvalid(rvalid), .rready(rready),
        .sample_clk(clk), .tex_rd_en(gs_tex_rd_en_o), .tex_rd_addr(gs_tex_rd_addr_o),
        .tex_rd_data(tex_cache_data), .tex_ready(tex_cache_ready)
    );
    logic [31:0] lpddr_mem [0:(TEX_BYTES/4)-1];       // reloaded: tex A, then tex B
    typedef enum logic [1:0] { S_IDLE, S_WAIT, S_DATA } sstate_t; sstate_t sst; logic [3:0] tdly; int tbeat;
    always_ff @(posedge clk) begin
        if (!rst_n) begin sst<=S_IDLE; arready<=0; rvalid<=0; rlast<=0; rresp<=0; rdata<=0; tdly<=0; end
        else begin arready<=0; rvalid<=0; rlast<=0;
            case (sst)
                S_IDLE: if (arvalid) begin arready<=1; tbeat<=(araddr-LPDDR_TEX_BASE)>>5; tdly<=4'd2; sst<=S_WAIT; end
                S_WAIT: if (tdly==0) sst<=S_DATA; else tdly<=tdly-1'b1;
                S_DATA: if (rready) begin for (int w=0;w<8;w++) rdata[w*32 +: 32]<=lpddr_mem[tbeat*8+w];
                        rresp<=2'b00; rvalid<=1; rlast<=1; sst<=S_IDLE; end
            endcase
        end
    end

    // render epoch (per scene) + PSMCT32 writer + precleared LPDDR FB
    logic fb_flush=0, render_inflight=0, feeder_ready_q=0; int eof_count;
    wire feeder_ready_rise = feeder_ready_tb && !feeder_ready_q;
    always_ff @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin render_inflight<=0; feeder_ready_q<=0; fb_flush<=0; eof_count<=0; end
        else begin feeder_ready_q<=feeder_ready_tb; fb_flush<=1'b0;
            if (feeder_go_tb && feeder_ready_tb) render_inflight<=1'b1;
            if (render_inflight && feeder_ready_rise) begin fb_flush<=1'b1; render_inflight<=1'b0; eof_count<=eof_count+1; end
        end
    end
    logic        wr_arm=0; logic [255:0] fbw_wdata; logic [31:0] fbw_wstrb, fbw_awaddr; logic fbw_awvalid, fbw_wvalid;
    logic [31:0] fbw_beats, fbw_ovf, fbw_bresp_err; logic fbw_idle, fbw_drained;
    gs_lpddr_axi_master #(.FIFO_DEPTH(64), .PIX_BYTES(4)) u_wr (
        .gs_clk(clk), .gs_rst_n(rst_n), .enable(1'b1),
        .arm(wr_arm), .canary(1'b0), .fb_base(32'h0), .ctrl_commit(fb_commit),
        .px_emit(flush_emit_w && (flush_psm_w==6'h00)), .px_addr(flush_addr_w), .px_pix32(flush_color32_w), .flush(fb_flush),
        .axi_clk(emif_clk), .axi_rst_n(rst_n),
        .awaddr(fbw_awaddr), .awlen(), .awsize(), .awburst(), .awid(), .awvalid(fbw_awvalid), .awready(1'b1),
        .wdata(fbw_wdata), .wstrb(fbw_wstrb), .wlast(), .wvalid(fbw_wvalid), .wready(1'b1),
        .bvalid(1'b1), .bready(), .bresp(2'b00),
        .beats_written(fbw_beats), .bursts_issued(), .bresp_err_count(fbw_bresp_err),
        .fifo_overflow_count(fbw_ovf), .idle(fbw_idle), .frame_drained(fbw_drained)
    );
    logic [7:0] fb [0:FB_BYTES-1]; logic [31:0] fb_awlat;
    always_ff @(posedge emif_clk) begin
        if (fbw_awvalid) fb_awlat<=fbw_awaddr;
        if (fbw_wvalid) for (int i=0;i<32;i++) if (fbw_wstrb[i]) begin
            int aa; aa=fb_awlat+i; if (aa>=0 && aa<FB_BYTES) fb[aa]<=fbw_wdata[i*8 +: 8]; end
    end
    logic [31:0] ideal [0:FB_WORDS-1];
    always_ff @(posedge clk) if (rst_n && flush_emit_w && (flush_psm_w==6'h00)) ideal[flush_addr_w>>2]<=flush_color32_w;

    // FRESH-DRAIN observer (Codex): count frame_drained low->high and high->low edges (emif domain).
    logic fd_q; int fd_rises, fd_falls;
    always_ff @(posedge emif_clk or negedge rst_n) begin
        if (!rst_n) begin fd_q<=0; fd_rises<=0; fd_falls<=0; end
        else begin fd_q<=fbw_drained;
            if (fbw_drained && !fd_q) fd_rises<=fd_rises+1;
            if (!fbw_drained && fd_q) fd_falls<=fd_falls+1;
        end
    end

    // scanout (320x381), host-gated: enable = scan_en (video_src) AND frame_drained
    logic scan_en=0; wire so_enable = scan_en & fbw_drained;
    logic [11:0] px, py; logic vsync, in_win; logic [7:0] so_r, so_g, so_b;
    logic so_underflow; logic [31:0] so_rd_errs; logic so_line_valid;
    logic [29:0] so_araddr; logic [1:0] so_arburst; logic [6:0] so_arid; logic [7:0] so_arlen;
    logic [2:0]  so_arsize; logic so_arvalid, so_arready;
    logic [255:0] so_rdata; logic [1:0] so_rresp; logic so_rlast, so_rvalid, so_rready;
    gs_lpddr_scanout_lb #(.FB_BASE(30'd0), .STRIDE_BYTES(STRIDE), .ROW_BEATS(ROW_BEATS),
                          .N_ROWS(H), .PSMCT32(1'b1)) u_scan (
        .axi_clk(emif_clk), .axi_rst_n(rst_n), .enable(so_enable),
        .video_clk(video_clk), .frame_start(vsync), .pixel_x(px), .pixel_y(py), .in_window(in_win),
        .r(so_r), .g(so_g), .b(so_b), .line_valid(so_line_valid), .underflow(so_underflow), .rd_errs(so_rd_errs),
        .araddr(so_araddr), .arburst(so_arburst), .arid(so_arid), .arlen(so_arlen), .arsize(so_arsize),
        .arvalid(so_arvalid), .arready(so_arready), .rdata(so_rdata), .rresp(so_rresp),
        .rlast(so_rlast), .rvalid(so_rvalid), .rready(so_rready)
    );
    logic [7:0] rlfsr=8'h3C; always_ff @(posedge emif_clk) rlfsr<={rlfsr[6:0], rlfsr[7]^rlfsr[5]^rlfsr[4]^rlfsr[3]};
    typedef enum logic [1:0] { R_IDLE, R_WAIT, R_DATA } rst_t; rst_t rst_state;
    logic [3:0] rdly; logic [29:0] rd_addr_l; int read_beats;
    logic [2:0] vs_e; wire vs_edge_e = vs_e[1] && !vs_e[2]; int fb_reads, fb_reads_last;
    always_ff @(posedge emif_clk or negedge rst_n) begin
        if (!rst_n) begin rst_state<=R_IDLE; so_arready<=0; so_rvalid<=0; so_rlast<=0; so_rresp<=0; so_rdata<=0; rdly<=0;
                          read_beats<=0; vs_e<=0; fb_reads<=0; fb_reads_last<=0; end
        else begin so_arready<=0; so_rvalid<=0; so_rlast<=0; vs_e<={vs_e[1:0], vsync};
            if (vs_edge_e) begin fb_reads_last<=fb_reads; fb_reads<=0; end
            case (rst_state)
                R_IDLE: if (so_arvalid) begin so_arready<=1; rd_addr_l<=so_araddr; rdly<=rlfsr[2:0]; rst_state<=R_WAIT; end
                R_WAIT: if (rdly==0) rst_state<=R_DATA; else rdly<=rdly-1'b1;
                R_DATA: if (so_rready) begin
                    for (int w=0;w<8;w++) begin int aa; aa=rd_addr_l+w*4;
                        so_rdata[w*32 +: 32] <= (aa+3<FB_BYTES) ? {fb[aa+3],fb[aa+2],fb[aa+1],fb[aa]} : 32'd0; end
                    so_rresp<=2'b00; so_rvalid<=1; so_rlast<=1; read_beats<=read_beats+1;
                    if (!vs_edge_e) fb_reads<=fb_reads+1; rst_state<=R_IDLE; end
            endcase
        end
    end
    logic vid_run=0; logic [11:0] rawx, rawy;
    always_ff @(posedge video_clk) begin
        if (!vid_run) begin rawx<=0; rawy<=0; end
        else if (rawx==H_TOT-1) begin rawx<=0; rawy<=(rawy==V_TOT-1)?12'd0:rawy+1'b1; end
        else rawx<=rawx+1'b1;
    end
    wire active = (rawx>=H_BP)&&(rawx<H_BP+H_ACT)&&(rawy>=V_BP)&&(rawy<V_BP+V_ACT);
    assign px=active?(rawx-H_BP):12'd0; assign py=(rawy>=V_BP&&rawy<V_BP+V_ACT)?(rawy-V_BP):12'd0;
    assign in_win=active; assign vsync=vid_run&&(rawx==0)&&(rawy==0);
    logic [11:0] px_q, py_q; logic inwin_q, run_q;
    always_ff @(posedge video_clk) begin px_q<=px; py_q<=py; inwin_q<=in_win; run_q<=vid_run; end
    int checked; initial checked=0; logic scoring=0;
    always_ff @(posedge video_clk) if (scoring && run_q) begin
        logic [7:0] er,eg,eb; logic [31:0] w;
        if (inwin_q) begin int aa; aa=py_q*STRIDE+px_q*4; w={fb[aa+3],fb[aa+2],fb[aa+1],fb[aa]}; er=w[7:0]; eg=w[15:8]; eb=w[23:16]; end
        else begin er=0; eg=0; eb=0; end
        checked++;
        if (so_r!==er||so_g!==eg||so_b!==eb) begin
            if (errors<12) $error("[scan] px(%0d,%0d) got(%02x,%02x,%02x) exp(%02x,%02x,%02x)", px_q,py_q, so_r,so_g,so_b, er,eg,eb); errors++; end
    end

    // A->B composed reference + per-group palette/idx (for the oracle)
    logic [31:0] idxA [0:(512*512/4)-1]; logic [31:0] palA [0:255];
    logic [31:0] idxB [0:(512*512/4)-1]; logic [31:0] palB [0:255]; logic [31:0] refmap [0:FB_WORDS-1];

    // ---- one-scene runner: GO, wait render+drain, and REQUIRE frame_drained high->low->high (fresh, not stale) ----
    task automatic run_scene(input string nm, input int exp_records);
        int r0, f0, d=0; logic fd_before;
        r0=fd_rises; f0=fd_falls; fd_before=fbw_drained;      // stale high from a PRIOR scene?
        @(negedge clk); feeder_go_tb=1'b1; @(negedge clk); feeder_go_tb=1'b0;
        // ready drops (render started)
        d=0; while (feeder_ready_tb && d<4000) begin @(posedge clk); d++; end
        if (feeder_ready_tb!==1'b0) begin $error("[mt] %s: feeder_ready did not drop after GO", nm); errors++; end
        // ANTI-STALE (Codex): if frame_drained was HIGH before GO (a prior scene's drain), require a FALL first — proves
        // THIS scene's beats actually flowed and cleared the stale high (never accept a lingering 1 as this scene done).
        if (fd_before) begin
            d=0; while (fd_falls==f0 && d<800000) begin @(posedge emif_clk); d++; end
            if (fd_falls==f0) begin $error("[mt] %s: frame_drained never fell from stale high — STALE drain (scene did not render fresh)", nm); errors++; end
        end
        // require a fresh RISE (this scene's ordered drain) either way -> high->low->high for B, low->high for A.
        d=0; while (fd_rises<=r0 && d<800000) begin @(posedge emif_clk); d++; end
        if (fd_rises<=r0) begin $error("[mt] %s: frame_drained never rose — scene did not drain", nm); errors++; end
        repeat(100) @(posedge clk);
        if (feeder_records_w!==exp_records) begin $error("[mt] %s: records_emitted=%0d exp %0d", nm, feeder_records_w, exp_records); errors++; end
        if (fbw_ovf!==0 || fbw_bresp_err!==0) begin $error("[mt] %s: writer ovf=%0d bresp=%0d", nm, fbw_ovf, fbw_bresp_err); errors++; end
        $display("[mt] scene %s: fresh drain (falls %0d->%0d, rises %0d->%0d), records=%0d, ovf=0", nm, f0, fd_falls, r0, fd_rises, feeder_records_w);
    endtask

    task automatic fill_cache(input string nm, input logic [31:0] exp_crc);
        int d=0; logic d0;
        d0=fill_done;
        @(posedge clk) fill_start<=1'b1; @(posedge clk) fill_start<=1'b0;
        // require a FRESH fill_done low->high (cache rearm), not a lingering high
        d=0; while (fill_done && d<1000) begin @(posedge clk); d++; end          // wait it drops (busy)
        d=0; while (!fill_done && d<400000) begin @(posedge clk); d++; end        // then rises (done)
        if (!fill_done)                 begin $error("[mt] fill %s: fill_done never rose (rearm failed)", nm); errors++; end
        if (fill_crc_w!==exp_crc)       begin $error("[mt] fill %s: crc=%08x exp %08x", nm, fill_crc_w, exp_crc); errors++; end
        if (fill_beats!==N_BEATS)       begin $error("[mt] fill %s: beats=%0d exp %0d", nm, fill_beats, N_BEATS); errors++; end
        if (fill_bytes!==TEX_BYTES)     begin $error("[mt] fill %s: bytes=%0d exp %0d", nm, fill_bytes, TEX_BYTES); errors++; end
        if (tex_rd_errs!==0)            begin $error("[mt] fill %s: rd_errs=%0d", nm, tex_rd_errs); errors++; end
        $display("[mt] cache fill %s: fresh done, crc=0x%08x (exp %08x), beats=%0d bytes=%0d rd_errs=0", nm, fill_crc_w, exp_crc, fill_beats, fill_bytes);
    endtask

    // group-flag texel lookup — reads the module-level arrays (NO per-call array copy). gb=1 -> group B, else A.
    function automatic logic [23:0] cellg(input bit gb, input integer u, input integer v);
        integer lin; logic [31:0] w; logic [7:0] ix;
        lin=v*TW+u; w = gb ? idxB[lin/4] : idxA[lin/4]; ix=w[(8*(lin%4)) +: 8];
        cellg = gb ? palB[ix][23:0] : palA[ix][23:0];
    endfunction

    string only_m; string fdump; int mode;   // +ONLY=AB|A|B  ; +FBDUMP=<file>  (Codex isolation/composition diagnostic)
    initial begin
        errors=0; feeder_go_tb=1'b0; fill_start=1'b0; wr_arm=0; scan_en=0;
        if (!$value$plusargs("ONLY=%s", only_m)) only_m="AB";
        mode = (only_m=="A") ? 0 : (only_m=="B") ? 1 : 2;   // 0=A-only(palA) 1=B-only(palB) 2=AB(both)
        for (int i=0;i<FB_WORDS;i++) ideal[i]=32'd0;
        for (int i=0;i<FB_BYTES;i++) fb[i]=8'h00;                      // PRECLEAR EXACTLY ONCE
        idxA[0]='x;
        $readmemh("../../data/top_psmct32_raster_demo/sh3_mtA_idx.mem", idxA);
        $readmemh("../../data/top_psmct32_raster_demo/sh3_mtA_pal.mem", palA);
        $readmemh("../../data/top_psmct32_raster_demo/sh3_mtB_idx.mem", idxB);
        $readmemh("../../data/top_psmct32_raster_demo/sh3_mtB_pal.mem", palB);
        if (mode==0)      $readmemh("../../data/top_psmct32_raster_demo/sh3_mtA_refmap.mem", refmap);
        else if (mode==1) $readmemh("../../data/top_psmct32_raster_demo/sh3_mtB_refmap.mem", refmap);
        else              $readmemh("../../data/top_psmct32_raster_demo/sh3_mt_refmap.mem", refmap);
        $display("[mt] ONLY=%s (mode=%0d)", only_m, mode);
        if (idxA[0]===32'bx) begin $display("[tb_top_psmct32_sh3_multitex] SKIP — sh3_mt*.mem absent (run gs_make_sh3_multitex_fixture.py --emit)"); $finish; end

        rst_n=1'b0; core_go=1'b0; repeat(6) @(posedge clk); rst_n=1'b1; repeat(8) @(posedge clk);

        // boot the bootlet (uploads BOTH relocated CLUTs to CBP_A, CBP_B)
        @(negedge clk); core_go=1'b1; @(negedge clk); core_go=1'b0;
        wait (core_halt==1'b1); repeat(4) @(posedge clk);
        wait (dma_done_seen==1'b1); repeat(10) @(posedge clk);
        if (dut.xfer_busy==1'b1) wait (dut.xfer_busy==1'b0);
        wait (feeder_ready_tb==1'b1); repeat(50) @(posedge clk);
        wr_arm<=1'b1; repeat(40) @(posedge clk);

        // ===== SCENE A (runs in AB and A-only): texture A -> cache (fill #1), stage list A, GO, fresh drain =====
        if (mode!=1) begin
            $readmemh("../../data/top_psmct32_raster_demo/sh3_mtA_tex_lpddr.mem", lpddr_mem);
            fill_cache("A", CRC_TEX_A);
            $readmemh("../../data/top_psmct32_raster_demo/feeder_sh3_mtA.mem", dut.g_feeder.feeder_stg);
            run_scene("A", NTRIS_A);
            if (mode==2 && scan_en!==1'b0) begin $error("[mt] scanout enabled before scene B"); errors++; end
        end
        // ===== SCENE B (runs in AB and B-only): REBIND texture B -> cache (fill #2 rearm), stage list B, GO, drain =====
        if (mode!=0) begin
            $readmemh("../../data/top_psmct32_raster_demo/sh3_mtB_tex_lpddr.mem", lpddr_mem);
            fill_cache("B", CRC_TEX_B);
            $readmemh("../../data/top_psmct32_raster_demo/feeder_sh3_mtB.mem", dut.g_feeder.feeder_stg);
            run_scene("B", NTRIS_B);
        end

        // enable scanout only after the final fresh drain
        scan_en<=1'b1; repeat(20) @(posedge clk);
        if (mode==2) begin
            if (fd_rises<2) begin $error("[mt] expected 2 ordered drains (A,B): rises=%0d", fd_rises); errors++; end
            if (fd_falls<1) begin $error("[mt] scene B never cleared the stale drain (falls=%0d) — stale-drain race", fd_falls); errors++; end
        end else if (fd_rises<1) begin $error("[mt] isolated scene did not drain: rises=%0d", fd_rises); errors++; end

        // ===== scanout: score final FB vs the A->B reference; overlap separately =====
        vid_run=1;
        begin int d=0; while(!vsync && d<300000) begin @(posedge video_clk); d++; end end
        @(posedge video_clk); while(!vsync) @(posedge video_clk);
        begin scoring=1; @(posedge video_clk); while(!vsync) @(posedge video_clk); scoring=0; repeat(60) @(posedge emif_clk);
            if (fb_reads_last!==BEATS_PER_FRAME) begin $error("[mt] scanout beats/frame=%0d exp %0d", fb_reads_last, BEATS_PER_FRAME); errors++; end
        end
        if (so_underflow!==0) begin $error("[mt] scanout underflow"); errors++; end
        if (so_rd_errs !==0)  begin $error("[mt] scanout rd_errs=%0d", so_rd_errs); errors++; end
        if (checked < H_ACT*V_ACT) begin $error("[mt] only %0d px checked (exp >= %0d)", checked, H_ACT*V_ACT); errors++; end

        // The reference stored (tu,tv) of the WINNING group per pixel (B on overlap, else the covering group). Since
        // the per-pixel owner-group is not encoded, accept the RTL colour if it matches the <=1-texel neighbourhood in
        // EITHER palette A or B (multi-texture: the winning group's texel is one of the two). overlap (bit28) scored
        // separately. clut_bad requires the colour to exist in palette A OR B.
        begin
            int m_tot,m_ok,o_tot,o_ok,cb,D; bit mt; m_tot=0;m_ok=0;o_tot=0;o_ok=0;cb=0;
            for (int y=0;y<H;y++) for (int x=0;x<W;x++) begin
                logic [31:0] rm; logic [23:0] fbc; int tu,tv; bit ovl; rm=refmap[y*W+x];
                if (rm[31]) begin
                    tu=(rm>>9)&9'h1FF; tv=rm&9'h1FF; ovl=rm[28]; fbc=ideal[y*W+x][23:0]; m_tot++; D=9;
                    for (int rad=0;rad<=1 && D==9;rad++) for (int du=-rad;du<=rad;du++) for (int dv=-rad;dv<=rad;dv++) begin
                        int ch; ch=(du<0?-du:du); if((dv<0?-dv:dv)>ch) ch=(dv<0?-dv:dv);
                        if (ch==rad && D==9 && (tu+du)>=0 && (tu+du)<TW && (tv+dv)>=0 && (tv+dv)<TH) begin
                            mt = (mode==0) ? (fbc===cellg(1'b0,tu+du,tv+dv))               // A-only: palette A
                               : (mode==1) ? (fbc===cellg(1'b1,tu+du,tv+dv))               // B-only: palette B
                               :             (fbc===cellg(1'b0,tu+du,tv+dv) || fbc===cellg(1'b1,tu+du,tv+dv));
                            if (mt) D=rad;
                        end
                    end
                    if (D<=1) m_ok++;
                    if (ovl) begin o_tot++; if (D<=1) o_ok++; end
                    // clut_bad = a pixel the RTL ACTUALLY WROTE (ideal!=0) whose colour is not in the expected palette.
                    // Reference-covered pixels the RTL left black at a coverage edge (ideal==0) are texel misses (already
                    // penalized in <=1texel), NOT wrong-CLUT — do not count them here.
                    if (ideal[y*W+x]!==32'd0) begin bit f; f=1'b0; for (int i=0;i<256;i++)
                        if ((mode!=1 && palA[i][23:0]===fbc) || (mode!=0 && palB[i][23:0]===fbc)) f=1'b1;
                        if(!f) cb++; end
                end
            end
            $display("[mt][oracle] ONLY=%s <=1texel ALL=%0d/%0d (%.1f%%)  OVERLAP(A&B)=%0d/%0d (%.1f%%)  clut_bad=%0d",
                     only_m, m_ok,m_tot,(m_tot>0)?100.0*m_ok/m_tot:0.0, o_ok,o_tot,(o_tot>0)?100.0*o_ok/o_tot:0.0, cb);
            if (cb!==0)     begin $error("[mt][oracle] ONLY=%s: %0d covered px not in the expected palette", only_m, cb); errors++; end
            if (mode==2) begin
                if (o_tot<500)  begin $error("[mt][oracle] only %0d overlap px — accumulation not exercised", o_tot); errors++; end
                // OVERLAP is the composite proof (B over A). ALL reported. Per-draw A/B fidelity settled by the ONLY=A/B runs.
                if (o_tot>0 && (100.0*o_ok/o_tot)<95.0) begin $error("[mt][oracle] OVERLAP composite <=1texel %.1f%% < 95%%", 100.0*o_ok/o_tot); errors++; end
            end
        end
        // FB dump for the Codex composition check (A-only + B-only -> compose -> compare AB combined)
        if ($value$plusargs("FBDUMP=%s", fdump)) begin
            int fh; fh=$fopen(fdump,"w");
            for (int y=0;y<H;y++) for (int x=0;x<W;x++) begin int aa; aa=y*STRIDE+x*4; $fwrite(fh,"%08x\n",{fb[aa+3],fb[aa+2],fb[aa+1],fb[aa]}); end
            $fclose(fh); $display("[mt] dumped RTL FB (%0dx%0d) -> %s", W, H, fdump);
        end

        $display("[tb_top_psmct32_sh3_multitex] checked=%0d beats/frame=%0d (exp %0d) fresh_drains(rise/fall)=%0d/%0d records=%0d underflow=%0b ovf=%0d errors=%0d",
                 checked, fb_reads_last, BEATS_PER_FRAME, fd_rises, fd_falls, feeder_records_w, so_underflow, fbw_ovf, errors);
        if (errors==0) $display("[tb_top_psmct32_sh3_multitex] PASS"); else $display("[tb_top_psmct32_sh3_multitex] FAIL");
        $finish;
    end
    initial begin #120000000; $error("[tb_top_psmct32_sh3_multitex] TIMEOUT"); $finish; end
endmodule : tb_top_psmct32_sh3_multitex