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retroDE_ps2/sim/tb/gif_gs/tb_gs_tri_interp.sv
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thejayman77 ec82764bef Initial commit: retroDE_ps2 — first-of-its-kind PS2 GS FPGA core (DE25-Nano / Agilex 5) 
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>
2026-06-29 20:10:50 -04:00

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// retroDE_ps2 — tb_gs_tri_interp (Brick 3)
//
// White-box focused TB for the SYNTHESIZABLE non-axis-aligned triangle
// rasterizer: screen-space-affine interpolation of Gouraud COLOR and
// DEPTH (Z), with NO per-pixel divide and NO `// synthesis translate_off`
// on the live path.
//
// Two checks:
//
// (1) COVERAGE + COLOR — a Gouraud triangle (3 distinct vertex colors)
// with a NON-axis-aligned edge is drawn WITHOUT Z-test. The TB
// captures every raster_pixel emit and asserts:
// * pixels strictly inside the triangle (per an independent
// reference edge-function + top-left fill rule) are emitted;
// * pixels outside are NOT emitted (no spurious coverage);
// * the emitted color at a handful of interior pixels matches
// the expected AFFINE interpolation (and is within 1 LSB of
// the exact barycentric ground truth — affine == barycentric
// for affine attributes, modulo Q16.16 rounding).
//
// (2) DEPTH (Z) — a second Gouraud triangle with 3 DISTINCT vertex Z
// values is drawn with Z-test ALWAYS (z_rd_data tied to 0). The
// TB probes the white-box s2_interp_z at a few interior pixels and
// asserts it matches the expected affine Z plane (within 1 LSB of
// the barycentric Z), proving per-pixel interpolated depth feeds
// the Brick-2b Z path.
//
// The interpolation path is synthesizable: this TB exercises the exact
// same RTL functions (grad_dadx/grad_dady + interp_affine8/interp_affine_z)
// that synthesis sees — there is no translate_off fork.
`timescale 1ns/1ps
module tb_gs_tri_interp;
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;
// Outputs (most tied off — we watch raster_* + whitebox).
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), // Z buffer cleared
.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
function automatic logic [63:0] xyz2z(input int x, input int y, input int z);
return {32'(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);
return {32'd0, 8'hFF, 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_XYZ2 = 8'h05;
localparam logic [7:0] R_FRAME_1 = 8'h4C;
localparam logic [7:0] R_TEST_1 = 8'h47;
localparam logic [7:0] R_ZBUF_1 = 8'h4E;
localparam logic [63:0] PRIM_TRI = 64'd3;
localparam logic [63:0] FRAME_1_VAL = 64'h0000_0000_0001_0000; // FBW=1, PSMCT32
// ----- Independent reference: edge functions, fill rule, barycentric -----
// Triangle vertices (set per primitive before reference calls).
int vx0, vy0, vx1, vy1, vx2, vy2;
int cr0, cg0, cb0, cr1, cg1, cb1, cr2, cg2, cb2;
int vz0, vz1, vz2;
int ref_det;
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
// Post-swap CCW reference (det>0). The DUT swaps v1<->v2 if the
// signed area is negative; this reference computes the signed area
// and mirrors that swap so L weights are interior-positive.
int sx1, sy1, sx2, sy2; // post-swap v1/v2 screen coords
int scr1, scg1, scb1, scr2, scg2, scb2, sz1, sz2;
task automatic setup_ref();
int sa;
sa = (vx1 - vx0) * (vy2 - vy0) - (vy1 - vy0) * (vx2 - vx0);
if (sa < 0) begin
sx1 = vx2; sy1 = vy2; sx2 = vx1; sy2 = vy1;
scr1 = cr2; scg1 = cg2; scb1 = cb2; sz1 = vz2;
scr2 = cr1; scg2 = cg1; scb2 = cb1; sz2 = vz1;
ref_det = -sa;
end else begin
sx1 = vx1; sy1 = vy1; sx2 = vx2; sy2 = vy2;
scr1 = cr1; scg1 = cg1; scb1 = cb1; sz1 = vz1;
scr2 = cr2; scg2 = cg2; scb2 = cb2; sz2 = vz2;
ref_det = sa;
end
endtask
// top-or-left predicate (post-swap CCW)
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
// Inside test using the same biased edge functions the DUT uses.
function automatic bit ref_inside(input int px, input int py);
int e0, e1, e2;
int 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
// Exact barycentric attribute (ground truth, rational/det) for an
// attribute with post-swap vertex values a0/a1/a2.
function automatic int ref_attr(input int px, input int py,
input int a0, input int a1, input int a2);
int L0, L1, L2; // -e1, -e2, -e0 (interior-positive)
int 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; // integer trunc toward 0 (matches HW divide)
endfunction
int errors;
int emit_inside_ok, emit_outside_bad, missing_inside;
// Coverage map captured from raster_pixel emits for the current prim.
bit covered [0:15][0:15];
logic [7:0] cap_r [0:15][0:15];
logic [7:0] cap_g [0:15][0:15];
logic [7:0] cap_b [0:15][0:15];
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_r[y][x] = 8'd0; cap_g[y][x] = 8'd0; cap_b[y][x] = 8'd0;
end
endtask
// Capture emits while armed.
bit cap_armed;
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_r[raster_pixel_y_q][raster_pixel_x_q] <= raster_pixel_color_q[7:0];
cap_g[raster_pixel_y_q][raster_pixel_x_q] <= raster_pixel_color_q[15:8];
cap_b[raster_pixel_y_q][raster_pixel_x_q] <= raster_pixel_color_q[23:16];
end
end
initial begin
errors = 0; emit_inside_ok = 0; emit_outside_bad = 0; missing_inside = 0;
cap_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);
// =====================================================================
// TEST 1 — Gouraud color, non-axis-aligned, no Z-test.
// v0=(2,1) RED, v1=(13,2) GREEN, v2=(5,7) BLUE.
// =====================================================================
vx0=2; vy0=1; cr0=8'hFF; cg0=0; cb0=0; vz0=0;
vx1=13;vy1=2; cr1=0; cg1=8'hFF; cb1=0; vz1=0;
vx2=5; vy2=7; cr2=0; cg2=0; cb2=8'hFF; vz2=0;
setup_ref();
cap_armed = 1'b1;
drive_reg(R_PRIM, PRIM_TRI);
drive_reg(R_FRAME_1, FRAME_1_VAL);
drive_reg(R_RGBAQ, rgbaq(cr0,cg0,cb0));
drive_reg(R_XYZ2, xyz2z(vx0,vy0,vz0));
drive_reg(R_RGBAQ, rgbaq(cr1,cg1,cb1));
drive_reg(R_XYZ2, xyz2z(vx1,vy1,vz1));
drive_reg(R_RGBAQ, rgbaq(cr2,cg2,cb2));
drive_reg(R_XYZ2, xyz2z(vx2,vy2,vz2)); // closes
drive_idle();
repeat (260) @(posedge clk);
cap_armed = 1'b0;
@(posedge clk);
// Coverage + color checks against the reference.
for (int y = 0; y < 16; y++) begin
for (int x = 0; x < 16; x++) begin
bit want;
want = ref_inside(x, y);
if (want && !covered[y][x]) begin
$error("[T1 coverage] inside pixel (%0d,%0d) NOT drawn", x, y);
missing_inside = missing_inside + 1; errors = errors + 1;
end else if (!want && covered[y][x]) begin
$error("[T1 coverage] outside pixel (%0d,%0d) WAS drawn", x, y);
emit_outside_bad = emit_outside_bad + 1; errors = errors + 1;
end else if (want && covered[y][x]) begin
emit_inside_ok = emit_inside_ok + 1;
end
end
end
// Spot-check interpolated color at interior pixels vs barycentric
// ground truth (affine == barycentric within 1 LSB).
chk_color(7, 3);
chk_color(5, 4);
chk_color(9, 4);
chk_color(6, 2);
if (raster_overflow) begin $error("[T1] raster_overflow"); errors=errors+1; end
if (raster_degenerate) begin $error("[T1] raster_degenerate"); errors=errors+1; end
// =====================================================================
// TEST 2 — interpolated DEPTH. Gouraud triangle with distinct vertex
// Z, Z-test active (ALWAYS, cleared Z buffer). Probe s2_interp_z.
// v0=(2,1) z=0x100, v1=(13,2) z=0x700, v2=(5,7) z=0x400.
// =====================================================================
vx0=2; vy0=1; cr0=8'hFF; cg0=0; cb0=0; vz0=32'h100;
vx1=13;vy1=2; cr1=0; cg1=8'hFF; cb1=0; vz1=32'h700;
vx2=5; vy2=7; cr2=0; cg2=0; cb2=8'hFF; vz2=32'h400;
setup_ref();
// TEST_1.ZTE=1, ZTST=ALWAYS(1). ZBUF ZBP=2 PSMZ32 ZMSK=0.
drive_reg(R_PRIM, PRIM_TRI);
drive_reg(R_FRAME_1, FRAME_1_VAL);
drive_reg(R_TEST_1, (64'd1 << 16) | (64'd1 << 17)); // ZTE=1, ALWAYS
drive_reg(R_ZBUF_1, 64'd2); // ZBP=2, PSMZ32, ZMSK=0
drive_reg(R_RGBAQ, rgbaq(cr0,cg0,cb0));
drive_reg(R_XYZ2, xyz2z(vx0,vy0,vz0));
drive_reg(R_RGBAQ, rgbaq(cr1,cg1,cb1));
drive_reg(R_XYZ2, xyz2z(vx1,vy1,vz1));
drive_reg(R_RGBAQ, rgbaq(cr2,cg2,cb2));
drive_reg(R_XYZ2, xyz2z(vx2,vy2,vz2)); // closes
drive_idle();
// Probe s2_interp_z across the scan (collected by the monitor below).
repeat (520) @(posedge clk);
if (z_probe_checks == 0) begin
$error("[T2] no interior Z pixels observed");
errors = errors + 1;
end
$display("[tb_gs_tri_interp] T1 inside_ok=%0d missing=%0d outside_bad=%0d | T2 z_checks=%0d errors=%0d",
emit_inside_ok, missing_inside, emit_outside_bad, z_probe_checks, errors);
if (errors == 0) $display("[tb_gs_tri_interp] PASS");
else $display("[tb_gs_tri_interp] FAIL");
$finish;
end
// Color spot-check: compare DUT-captured color to barycentric ground
// truth with 1-LSB tolerance.
task automatic chk_color(input int x, input int y);
int er, eg, eb;
if (!ref_inside(x, y)) begin
// outside the triangle — not a meaningful color spot
end else if (!covered[y][x]) begin
$error("[T1 color] (%0d,%0d) inside but not covered", x, y);
errors = errors + 1;
end else begin
er = ref_attr(x, y, cr0, scr1, scr2);
eg = ref_attr(x, y, cg0, scg1, scg2);
eb = ref_attr(x, y, cb0, scb1, scb2);
if (absdiff(cap_r[y][x], er) > 1 ||
absdiff(cap_g[y][x], eg) > 1 ||
absdiff(cap_b[y][x], eb) > 1) begin
$error("[T1 color] (%0d,%0d) got (%0d,%0d,%0d) expected ~(%0d,%0d,%0d)",
x, y, cap_r[y][x], cap_g[y][x], cap_b[y][x], er, eg, eb);
errors = errors + 1;
end else begin
$display("[T1 color] (%0d,%0d) got (%0d,%0d,%0d) ref (%0d,%0d,%0d) OK",
x, y, cap_r[y][x], cap_g[y][x], cap_b[y][x], er, eg, eb);
end
end
endtask
function automatic int absdiff(input int a, input int b);
return (a > b) ? (a - b) : (b - a);
endfunction
// ----- Ch296 multiplier-resize guard: the per-pixel interp multiplier
// operands dx/dy were narrowed to signed 16 bits. Assert at every live
// S2 cycle that the white-box s2_dx/s2_dy actually stay inside signed
// 16-bit range (true bound is ±4095 from 12-bit screen coords). If a
// future change widens screen coords past this, the resize is no longer
// lossless and this fires.
always_ff @(posedge clk) begin
if (rst_n && u_gs.s2_valid_q) begin
if ($signed(u_gs.s2_dx) > 32767 || $signed(u_gs.s2_dx) < -32768) begin
$error("[dx range] s2_dx=%0d out of signed-16 range", $signed(u_gs.s2_dx));
errors = errors + 1;
end
if ($signed(u_gs.s2_dy) > 32767 || $signed(u_gs.s2_dy) < -32768) begin
$error("[dy range] s2_dy=%0d out of signed-16 range", $signed(u_gs.s2_dy));
errors = errors + 1;
end
end
end
// ----- T2 Z probe: watch the whitebox s2_interp_z at interior S2 pixels.
int z_probe_checks;
initial z_probe_checks = 0;
bit z_probe_armed;
always_ff @(posedge clk) begin
if (rst_n && z_probe_armed
&& u_gs.s2_valid_q && u_gs.s2_inside_q
&& u_gs.ras_tri_active) begin
int px, py;
int ez;
px = int'(u_gs.s2_x_q);
py = int'(u_gs.s2_y_q);
if (px < 16 && py < 16 && ref_inside(px, py)) begin
ez = ref_attr(px, py, vz0, sz1, sz2);
if (absdiff(int'(u_gs.s2_interp_z), ez) > 1) begin
$error("[T2 Z] (%0d,%0d) s2_interp_z=%0d expected ~%0d",
px, py, u_gs.s2_interp_z, ez);
errors = errors + 1;
end else begin
z_probe_checks = z_probe_checks + 1;
end
end
end
end
// Arm the Z probe only during TEST 2 (after T1 finishes). T1 has
// vz*=0 so its s2_interp_z is trivially 0; gate on a nonzero vertex Z.
always_comb z_probe_armed = (vz1 != 0);
initial begin
#5000000;
$error("[tb_gs_tri_interp] timeout");
$finish;
end
endmodule : tb_gs_tri_interp
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