// retroDE_ps2 — tb_gs_fog // // Focused white-box TB for GS per-vertex FOG in the reduced rasterizer. // // PS2 GS fog: final_color_channel = (C * F + FOGCOL * (255 - F)) >> 8, per // RGB channel, where F is the 8-bit per-vertex fog coefficient (XYZF2 bits // [63:56]) interpolated affinely across the primitive (flat for a SPRITE), // gated on PRIM.FGE (bit 5). FOGCOL is GIF reg 0x3D (low 24 bits = 0xBBGGRR). // Alpha is NOT fogged. When FGE=0 the emit is byte-identical to the no-fog // path — the hard invariant. // // Tests: // T1 — FGE=1 triangle, FLAT color, FLAT F. Assert the emitted RGB equals the // EXACT hand-computed fog blend at several interior pixels, and the // alpha is preserved unchanged. // T2 — FGE=1 triangle, FLAT color, DISTINCT per-vertex F. Probe the white-box // s2_fog_f at interior S2 pixels and assert it matches the barycentric // (ground-truth) interpolated F within 1 LSB — proving F rides the // shared affine gradient engine like the colour/Z attributes. // T3 — FGE=0 triangle, SAME geometry/color as T1 with FOGCOL still set. // Assert the emitted color is BYTE-IDENTICAL to the raw vertex color // (no fog applied) — the non-negotiable invariant. // T4 — FGE=1 SPRITE, flat color, flat F. Assert the exact fog blend on the // flat-sprite emit path (s2_sprite_color64 chokepoint). `timescale 1ns/1ps module tb_gs_fog; logic clk; logic rst_n; initial clk = 1'b0; always #5 clk = ~clk; logic gif_reg_wr_en; logic [7:0] gif_reg_num; logic [63:0] gif_reg_data; logic [7:0] bg_r, bg_g, bg_b; logic [63:0] prim_q, rgbaq_q, xyz2_q, xyzf2_q, frame_1_q, zbuf_1_q; logic prim_complete; logic [31:0] prim_complete_count; logic [63:0] prim_v0_q, prim_v1_q, prim_v2_q; logic [63:0] prim_color_q; logic [63:0] prim_color_v0_q, prim_color_v1_q, prim_color_v2_q; trace_pkg::vertex_t prim_v0_decoded_q, prim_v1_decoded_q, prim_v2_decoded_q; trace_pkg::color_t prim_v0_color_decoded_q, prim_v1_color_decoded_q, prim_v2_color_decoded_q; logic pixel_emit; logic [31:0] pixel_emit_count; logic [11:0] pixel_x_q, pixel_y_q; logic [63:0] pixel_color_q; logic [8:0] pixel_fbp_q; logic [5:0] pixel_fbw_q, pixel_psm_q; logic [31:0] pixel_fb_addr_q; logic raster_pixel_emit; logic [31:0] raster_pixel_emit_count; logic [11:0] raster_pixel_x_q, raster_pixel_y_q; logic [63:0] raster_pixel_color_q; logic [31:0] raster_pixel_fb_addr_q; logic [3:0] raster_pixel_be_q; logic [31:0] raster_pixel_mask_q; logic [5:0] raster_pixel_psm_q; logic raster_active; logic raster_overflow; logic raster_fifo_full; logic raster_degenerate; logic tex_rd_en; logic [31:0] tex_rd_addr; logic fb_rd_en; logic [31:0] fb_rd_addr; logic z_rd_en; logic [31:0] z_rd_addr; logic ev_valid; trace_pkg::subsys_e ev_subsys; trace_pkg::event_e ev_event; logic [63:0] ev_arg0, ev_arg1, ev_arg2, ev_arg3; logic [31:0] ev_flags; gs_stub u_gs ( .clk(clk), .rst_n(rst_n), .reg_wr_en(1'b0), .reg_wr_addr(16'd0), .reg_wr_data(64'd0), .gif_reg_wr_en(gif_reg_wr_en), .gif_reg_num(gif_reg_num), .gif_reg_data(gif_reg_data), .bg_r(bg_r), .bg_g(bg_g), .bg_b(bg_b), .prim_q(prim_q), .rgbaq_q(rgbaq_q), .xyz2_q(xyz2_q), .xyzf2_q(xyzf2_q), .frame_1_q(frame_1_q), .zbuf_1_q(zbuf_1_q), .prim_complete(prim_complete), .prim_complete_count(prim_complete_count), .prim_v0_q(prim_v0_q), .prim_v1_q(prim_v1_q), .prim_v2_q(prim_v2_q), .prim_color_q(prim_color_q), .prim_color_v0_q(prim_color_v0_q), .prim_color_v1_q(prim_color_v1_q), .prim_color_v2_q(prim_color_v2_q), .prim_v0_decoded_q(prim_v0_decoded_q), .prim_v1_decoded_q(prim_v1_decoded_q), .prim_v2_decoded_q(prim_v2_decoded_q), .prim_v0_color_decoded_q(prim_v0_color_decoded_q), .prim_v1_color_decoded_q(prim_v1_color_decoded_q), .prim_v2_color_decoded_q(prim_v2_color_decoded_q), .pixel_emit(pixel_emit), .pixel_emit_count(pixel_emit_count), .pixel_x_q(pixel_x_q), .pixel_y_q(pixel_y_q), .pixel_color_q(pixel_color_q), .pixel_fbp_q(pixel_fbp_q), .pixel_fbw_q(pixel_fbw_q), .pixel_psm_q(pixel_psm_q), .pixel_fb_addr_q(pixel_fb_addr_q), .raster_pixel_emit(raster_pixel_emit), .raster_pixel_emit_count(raster_pixel_emit_count), .raster_pixel_x_q(raster_pixel_x_q), .raster_pixel_y_q(raster_pixel_y_q), .raster_pixel_color_q(raster_pixel_color_q), .raster_pixel_fb_addr_q(raster_pixel_fb_addr_q), .raster_pixel_be_q(raster_pixel_be_q), .raster_pixel_mask_q(raster_pixel_mask_q), .raster_pixel_psm_q(raster_pixel_psm_q), .raster_active(raster_active), .raster_overflow(raster_overflow), .raster_fifo_full(raster_fifo_full), .raster_degenerate(raster_degenerate), .tex_rd_en(tex_rd_en), .tex_rd_addr(tex_rd_addr), .tex_rd_data(32'd0), .fb_rd_en(fb_rd_en), .fb_rd_addr(fb_rd_addr), .fb_rd_data(32'd0), .z_rd_en(z_rd_en), .z_rd_addr(z_rd_addr), .z_rd_data(32'd0), .ev_valid(ev_valid), .ev_subsys(ev_subsys), .ev_event(ev_event), .ev_arg0(ev_arg0), .ev_arg1(ev_arg1), .ev_arg2(ev_arg2), .ev_arg3(ev_arg3), .ev_flags(ev_flags) ); // ----- Drive helpers ----- task automatic drive_reg(input logic [7:0] num, input logic [63:0] data); @(negedge clk); gif_reg_wr_en = 1'b1; gif_reg_num = num; gif_reg_data = data; @(posedge clk); endtask task automatic drive_idle(); @(negedge clk); gif_reg_wr_en = 1'b0; gif_reg_num = 8'd0; gif_reg_data = 64'd0; @(posedge clk); endtask // XYZF2 (reg 0x04): X=[15:0] (12.4), Y=[31:16] (12.4), Z=[55:32] (24b), // F=[63:56] (8b fog). Screen coords carry no fractional bits here. function automatic logic [63:0] xyzf2(input int x, input int y, input int z, input int f); return {8'(f), 24'(z), 12'(y), 4'd0, 12'(x), 4'd0}; endfunction function automatic logic [63:0] rgbaq(input int r, input int g, input int b, input int a); return {32'd0, 8'(a), 8'(b), 8'(g), 8'(r)}; endfunction localparam logic [7:0] R_PRIM = 8'h00; localparam logic [7:0] R_RGBAQ = 8'h01; localparam logic [7:0] R_XYZF2 = 8'h04; localparam logic [7:0] R_FOGCOL = 8'h3D; localparam logic [7:0] R_FRAME_1 = 8'h4C; localparam logic [63:0] PRIM_TRI = 64'd3; // TRI localparam logic [63:0] PRIM_TRI_FGE = 64'd3 | (64'd1 << 5); // TRI + FGE localparam logic [63:0] PRIM_SPRITE_FGE = 64'd6 | (64'd1 << 5); // SPRITE + FGE localparam logic [63:0] FRAME_1_VAL = 64'h0000_0000_0001_0000; // FBW=1, PSMCT32 // FOGCOL = 0xBBGGRR localparam int FOG_R = 8'h20; localparam int FOG_G = 8'h40; localparam int FOG_B = 8'h60; localparam logic [63:0] FOGCOL_VAL = {40'd0, 8'(FOG_B), 8'(FOG_G), 8'(FOG_R)}; // Reference fog blend (matches RTL fog_blend_abgr exactly). function automatic int fog_ch(input int c, input int f, input int fc); return (c * f + fc * (255 - f)) >> 8; endfunction function automatic int absdiff(input int a, input int b); return (a > b) ? (a - b) : (b - a); endfunction // ----- Independent triangle reference (edge fn, fill rule, barycentric) ----- int vx0, vy0, vx1, vy1, vx2, vy2; int vf0, vf1, vf2; int ref_det; int sx1, sy1, sx2, sy2, sf1, sf2; function automatic int edge_f(input int px, input int py, input int ax, input int ay, input int bx, input int by); return (px - ax) * (by - ay) - (py - ay) * (bx - ax); endfunction task automatic setup_ref(); int sa; sa = (vx1 - vx0) * (vy2 - vy0) - (vy1 - vy0) * (vx2 - vx0); if (sa < 0) begin sx1 = vx2; sy1 = vy2; sf1 = vf2; sx2 = vx1; sy2 = vy1; sf2 = vf1; ref_det = -sa; end else begin sx1 = vx1; sy1 = vy1; sf1 = vf1; sx2 = vx2; sy2 = vy2; sf2 = vf2; ref_det = sa; end endtask function automatic bit tol(input int ax, input int ay, input int bx, input int by); int dx, dy; dx = bx - ax; dy = by - ay; return (dy > 0) || ((dy == 0) && (dx > 0)); endfunction function automatic bit ref_inside(input int px, input int py); int e0, e1, e2, b0, b1, b2; e0 = edge_f(px, py, vx0, vy0, sx1, sy1); e1 = edge_f(px, py, sx1, sy1, sx2, sy2); e2 = edge_f(px, py, sx2, sy2, vx0, vy0); b0 = tol(vx0, vy0, sx1, sy1) ? 0 : 1; b1 = tol(sx1, sy1, sx2, sy2) ? 0 : 1; b2 = tol(sx2, sy2, vx0, vy0) ? 0 : 1; return ((e0 + b0) <= 0) && ((e1 + b1) <= 0) && ((e2 + b2) <= 0); endfunction function automatic int ref_attr(input int px, input int py, input int a0, input int a1, input int a2); int L0, L1, L2, num; L0 = -edge_f(px, py, sx1, sy1, sx2, sy2); L1 = -edge_f(px, py, sx2, sy2, vx0, vy0); L2 = -edge_f(px, py, vx0, vy0, sx1, sy1); num = L0 * a0 + L1 * a1 + L2 * a2; if (ref_det == 0) return 0; return num / ref_det; endfunction int errors; // ----- Emit capture (full 32-bit ABGR) ----- bit covered [0:15][0:15]; logic [31:0] cap_c [0:15][0:15]; bit cap_armed; task automatic clear_cov(); for (int y = 0; y < 16; y++) for (int x = 0; x < 16; x++) begin covered[y][x] = 1'b0; cap_c[y][x] = 32'd0; end endtask always_ff @(posedge clk) begin if (rst_n && cap_armed && raster_pixel_emit && raster_pixel_x_q < 16 && raster_pixel_y_q < 16) begin covered[raster_pixel_y_q][raster_pixel_x_q] <= 1'b1; cap_c [raster_pixel_y_q][raster_pixel_x_q] <= raster_pixel_color_q[31:0]; end end // ----- T2 F-interpolation probe: white-box s2_fog_f at interior pixels ----- int f_probe_checks; bit f_probe_armed; always_ff @(posedge clk) begin if (rst_n && f_probe_armed && u_gs.s2_valid_q && u_gs.s2_inside_q && u_gs.ras_tri_active) begin int px, py, ef; px = int'(u_gs.s2_x_q); py = int'(u_gs.s2_y_q); if (px < 16 && py < 16 && ref_inside(px, py)) begin ef = ref_attr(px, py, vf0, sf1, sf2); if (absdiff(int'(u_gs.s2_fog_f), ef) > 1) begin $error("[T2 F] (%0d,%0d) s2_fog_f=%0d expected ~%0d", px, py, u_gs.s2_fog_f, ef); errors = errors + 1; end else begin f_probe_checks = f_probe_checks + 1; end end end end // Exact fog-blend spot check on a captured emitted pixel. task automatic chk_fog(input int x, input int y, input int cr, input int cg, input int cb, input int ca, input int f); int er, eg, eb; er = fog_ch(cr, f, FOG_R); eg = fog_ch(cg, f, FOG_G); eb = fog_ch(cb, f, FOG_B); if (!covered[y][x]) begin $error("[fog] (%0d,%0d) expected covered but was not", x, y); errors = errors + 1; end else if (cap_c[y][x][7:0] !== er[7:0] || cap_c[y][x][15:8] !== eg[7:0] || cap_c[y][x][23:16] !== eb[7:0]) begin $error("[fog] (%0d,%0d) got (%0d,%0d,%0d) expected EXACT (%0d,%0d,%0d)", x, y, cap_c[y][x][7:0], cap_c[y][x][15:8], cap_c[y][x][23:16], er, eg, eb); errors = errors + 1; end else if (cap_c[y][x][31:24] !== ca[7:0]) begin $error("[fog] (%0d,%0d) alpha fogged: got %0d expected %0d (unchanged)", x, y, cap_c[y][x][31:24], ca); errors = errors + 1; end else begin $display("[fog] (%0d,%0d) got (%0d,%0d,%0d,a=%0d) EXACT OK", x, y, cap_c[y][x][7:0], cap_c[y][x][15:8], cap_c[y][x][23:16], cap_c[y][x][31:24]); end endtask // Exact no-fog (FGE=0 invariant): emitted RGB == raw color, alpha == raw. task automatic chk_nofog(input int x, input int y, input int cr, input int cg, input int cb, input int ca); if (!covered[y][x]) begin $error("[nofog] (%0d,%0d) expected covered but was not", x, y); errors = errors + 1; end else if (cap_c[y][x][7:0] !== cr[7:0] || cap_c[y][x][15:8] !== cg[7:0] || cap_c[y][x][23:16] !== cb[7:0] || cap_c[y][x][31:24] !== ca[7:0]) begin $error("[nofog] (%0d,%0d) FGE=0 NOT byte-identical: got %08x expected raw (%0d,%0d,%0d,a=%0d)", x, y, cap_c[y][x], cr, cg, cb, ca); errors = errors + 1; end else begin $display("[nofog] (%0d,%0d) FGE=0 byte-identical raw color OK", x, y); end endtask // Flat triangle constants. localparam int TC_R = 8'hC0, TC_G = 8'h80, TC_B = 8'h30, TC_A = 8'hFF; initial begin errors = 0; f_probe_checks = 0; cap_armed = 1'b0; f_probe_armed = 1'b0; rst_n = 1'b0; gif_reg_wr_en = 1'b0; gif_reg_num = 8'd0; gif_reg_data = 64'd0; clear_cov(); repeat (4) @(posedge clk); rst_n = 1'b1; repeat (2) @(posedge clk); // ================================================================ // T1 — FGE=1 triangle, FLAT color, FLAT F. Exact fog blend. // ================================================================ vx0=2; vy0=1; vf0=8'h40; vx1=13;vy1=2; vf1=8'h40; vx2=5; vy2=7; vf2=8'h40; setup_ref(); clear_cov(); cap_armed = 1'b1; drive_reg(R_FOGCOL, FOGCOL_VAL); drive_reg(R_PRIM, PRIM_TRI_FGE); drive_reg(R_FRAME_1, FRAME_1_VAL); drive_reg(R_RGBAQ, rgbaq(TC_R,TC_G,TC_B,TC_A)); drive_reg(R_XYZF2, xyzf2(vx0,vy0,0,vf0)); drive_reg(R_RGBAQ, rgbaq(TC_R,TC_G,TC_B,TC_A)); drive_reg(R_XYZF2, xyzf2(vx1,vy1,0,vf1)); drive_reg(R_RGBAQ, rgbaq(TC_R,TC_G,TC_B,TC_A)); drive_reg(R_XYZF2, xyzf2(vx2,vy2,0,vf2)); // closes drive_idle(); repeat (300) @(posedge clk); cap_armed = 1'b0; @(posedge clk); chk_fog(7, 3, TC_R, TC_G, TC_B, TC_A, 8'h40); chk_fog(5, 4, TC_R, TC_G, TC_B, TC_A, 8'h40); chk_fog(6, 2, TC_R, TC_G, TC_B, TC_A, 8'h40); if (raster_overflow || raster_degenerate) begin $error("[T1] raster anomaly"); errors = errors + 1; end // ================================================================ // T2 — FGE=1 triangle, FLAT color, DISTINCT per-vertex F. Probe the // white-box interpolated s2_fog_f vs barycentric ground truth. // ================================================================ vx0=2; vy0=1; vf0=8'h10; vx1=13;vy1=2; vf1=8'hF0; vx2=5; vy2=7; vf2=8'h80; setup_ref(); f_probe_armed = 1'b1; drive_reg(R_PRIM, PRIM_TRI_FGE); drive_reg(R_FRAME_1, FRAME_1_VAL); drive_reg(R_RGBAQ, rgbaq(TC_R,TC_G,TC_B,TC_A)); drive_reg(R_XYZF2, xyzf2(vx0,vy0,0,vf0)); drive_reg(R_RGBAQ, rgbaq(TC_R,TC_G,TC_B,TC_A)); drive_reg(R_XYZF2, xyzf2(vx1,vy1,0,vf1)); drive_reg(R_RGBAQ, rgbaq(TC_R,TC_G,TC_B,TC_A)); drive_reg(R_XYZF2, xyzf2(vx2,vy2,0,vf2)); // closes drive_idle(); repeat (320) @(posedge clk); f_probe_armed = 1'b0; @(posedge clk); if (f_probe_checks == 0) begin $error("[T2] no interior F pixels observed"); errors = errors + 1; end // ================================================================ // T3 — FGE=0 triangle, SAME geometry/color as T1, FOGCOL still set. // Emitted color MUST be byte-identical to the raw vertex color. // ================================================================ vx0=2; vy0=1; vf0=8'h40; vx1=13;vy1=2; vf1=8'h40; vx2=5; vy2=7; vf2=8'h40; setup_ref(); clear_cov(); cap_armed = 1'b1; drive_reg(R_PRIM, PRIM_TRI); // FGE = 0 drive_reg(R_FRAME_1, FRAME_1_VAL); drive_reg(R_RGBAQ, rgbaq(TC_R,TC_G,TC_B,TC_A)); drive_reg(R_XYZF2, xyzf2(vx0,vy0,0,vf0)); drive_reg(R_RGBAQ, rgbaq(TC_R,TC_G,TC_B,TC_A)); drive_reg(R_XYZF2, xyzf2(vx1,vy1,0,vf1)); drive_reg(R_RGBAQ, rgbaq(TC_R,TC_G,TC_B,TC_A)); drive_reg(R_XYZF2, xyzf2(vx2,vy2,0,vf2)); // closes drive_idle(); repeat (300) @(posedge clk); cap_armed = 1'b0; @(posedge clk); chk_nofog(7, 3, TC_R, TC_G, TC_B, TC_A); chk_nofog(5, 4, TC_R, TC_G, TC_B, TC_A); chk_nofog(6, 2, TC_R, TC_G, TC_B, TC_A); // ================================================================ // T4 — FGE=1 SPRITE, flat color, flat F. Exact fog blend on the // sprite emit chokepoint (s2_sprite_color64). // ================================================================ clear_cov(); cap_armed = 1'b1; drive_reg(R_PRIM, PRIM_SPRITE_FGE); drive_reg(R_FRAME_1, FRAME_1_VAL); drive_reg(R_RGBAQ, rgbaq(TC_R,TC_G,TC_B,TC_A)); drive_reg(R_XYZF2, xyzf2(1, 1, 0, 8'hA0)); // sprite origin vertex drive_reg(R_XYZF2, xyzf2(5, 5, 0, 8'hA0)); // closing vertex -> flat F=0xA0 drive_idle(); repeat (200) @(posedge clk); cap_armed = 1'b0; @(posedge clk); // Interior sprite pixels (rect [1,5)x[1,5)). chk_fog(2, 2, TC_R, TC_G, TC_B, TC_A, 8'hA0); chk_fog(3, 4, TC_R, TC_G, TC_B, TC_A, 8'hA0); chk_fog(4, 1, TC_R, TC_G, TC_B, TC_A, 8'hA0); $display("[tb_gs_fog] T2 f_checks=%0d errors=%0d", f_probe_checks, errors); if (errors == 0) $display("[tb_gs_fog] PASS"); else $display("[tb_gs_fog] FAIL"); $finish; end initial begin #5000000; $error("[tb_gs_fog] timeout"); $finish; end endmodule : tb_gs_fog