rtl/gfx: implement fixed-point FMA

3 files changed, 125 insertions, 3 deletions

diff --git a/rtl/gfx/gfx_defs.sv b/rtl/gfx/gfx_defs.sv
index 1d2bd68..45e1a63 100644
--- a/rtl/gfx/gfx_defs.sv
+++ b/rtl/gfx/gfx_defs.sv
@@ -14,7 +14,6 @@
 typedef logic[`FLOAT_BITS - 1:0]  fp;
 typedef fp                        vec2[2];
 typedef fp                        vec4[`FLOATS_PER_VEC];
-typedef fp[`FLOATS_PER_VEC - 1:0] vec4_packed;
 typedef vec4                      mat4[`VECS_PER_MAT];
 
 `define FP_UNIT 16'h3c00
@@ -48,10 +47,13 @@ typedef struct packed
 	logic[9:0] r, g, b;
 } rgb30;
 
-typedef logic signed[31:0] fixed;
-
 `define FIXED_FRAC 16
 
+`define FIXED_FMA_STAGES     5
+`define FIXED_FMA_DOT_STAGES (2 * `FIXED_FMA_STAGES)
+
+typedef logic signed[31:0] fixed;
+
 typedef struct packed
 {
 	fixed x, y;
diff --git a/rtl/gfx/gfx_fixed_fma.sv b/rtl/gfx/gfx_fixed_fma.sv
new file mode 100644
index 0000000..e1dd6bb
--- /dev/null
+++ b/rtl/gfx/gfx_fixed_fma.sv
@@ -0,0 +1,72 @@
+`include "gfx/gfx_defs.sv"
+
+/* Operación a * b + c en punto fijo, diseñada para cerrar timing fácilmente
+ * en Cyclone V donde los bloques de DSP soportan 18x18. Las etapas son:
+ * - fma_ab: Productos de permutaciones a_lo/hi con b_lo/hi
+ * - fma_pp: Recombinación en FMAs parciales
+ * - fma_lo: Mitad baja del resultado y mitad alta pre-carry
+ * - fma_hi: Mitad alta post-carry
+ *
+ * Nótese que esto toma exactamente el mismo trabajo que a * b
+ * (ver rtl/core/mul.sv en proyecto 2 de arqui 1).
+ */
+module gfx_fixed_fma
+(
+	input  logic clk,
+
+	input  fixed a,
+	             b,
+	             c,
+	input  logic stall,
+
+	output fixed q
+);
+
+	fixed a_ab, b_ab, c_ab, c_pp;
+	logic[1:0] carry;
+	logic[16:0] lo_left, lo_right;
+	logic[17:0] lo_with_carry;
+	logic[35:0] ab_ll, ab_lh, ab_hl, ab_hh;
+
+	logic[15:0] a_lo, a_hi, b_lo, b_hi, ab_ll_hi, ab_ll_lo, ab_hl_hi, ab_hl_lo,
+	            ab_lh_hi, ab_lh_lo, ab_hh_hi, ab_hh_lo, c_hi, c_lo, hi, hi_left, hi_right, lo;
+
+	assign {a_hi, a_lo} = a_ab;
+	assign {b_hi, b_lo} = b_ab;
+	assign {c_hi, c_lo} = c_pp;
+
+	assign {ab_ll_hi, ab_ll_lo} = ab_ll[31:0];
+	assign {ab_lh_hi, ab_lh_lo} = ab_lh[31:0];
+	assign {ab_hl_hi, ab_hl_lo} = ab_hl[31:0];
+	assign {ab_hh_hi, ab_hh_lo} = ab_hh[31:0];
+
+	assign {carry, lo} = lo_with_carry;
+
+	always @(posedge clk)
+		if (!stall) begin
+			a_ab <= a;
+			b_ab <= b;
+			c_ab <= c;
+
+			/* Como los operandos son pequeños (16 bits), esto no se sintetiza,
+			 * sino que se enruta a través de los bloques de DSP más cercanos
+			 */
+			ab_ll <= {2'd0, a_lo} * {2'd0, b_lo};
+			ab_lh <= {2'd0, a_lo} * {2'd0, b_hi};
+			ab_hl <= {2'd0, a_hi} * {2'd0, b_lo};
+			ab_hh <= {2'd0, a_hi} * {2'd0, b_hi};
+
+			c_pp <= c_ab;
+
+			hi_left <= ab_hh_lo + ab_lh_hi;
+			lo_left <= {1'd0, ab_lh_lo} + {1'd0, ab_hl_lo};
+			hi_right <= ab_hl_hi + c_hi;
+			lo_right <= {1'd0, ab_ll_hi} + {1'd0, c_lo};
+
+			hi <= hi_left + hi_right;
+			lo_with_carry <= {1'd0, lo_left} + {1'd0, lo_right};
+
+			q <= {hi + {14'd0, carry}, lo};
+		end
+
+endmodule
diff --git a/rtl/gfx/gfx_fixed_fma_dot.sv b/rtl/gfx/gfx_fixed_fma_dot.sv
new file mode 100644
index 0000000..2831d08
--- /dev/null
+++ b/rtl/gfx/gfx_fixed_fma_dot.sv
@@ -0,0 +1,48 @@
+`include "gfx/gfx_defs.sv"
+
+module gfx_fixed_fma_dot
+(
+	input  logic clk,
+
+	input  fixed a0,
+	             b0,
+	             a1,
+	             b1,
+	             c,
+	input  logic stall,
+
+	output fixed q
+);
+
+	fixed q0, a1_hold[`FIXED_FMA_STAGES], b1_hold[`FIXED_FMA_STAGES];
+
+	gfx_fixed_fma fma0
+	(
+		.a(a0),
+		.b(b0),
+		.q(q0),
+		.*
+	);
+
+	gfx_fixed_fma fma1
+	(
+		.a(a1_hold[`FIXED_FMA_STAGES - 1]),
+		.b(b1_hold[`FIXED_FMA_STAGES - 1]),
+		.c(q0),
+		.*
+	);
+
+	integer i;
+
+	always_ff @(posedge clk)
+		if (!stall) begin
+			a1_hold[0] <= a1;
+			b1_hold[0] <= b1;
+
+			for (i = 1; i < `FIXED_FMA_STAGES; ++i) begin
+				a1_hold[i] <= a1_hold[i - 1];
+				b1_hold[i] <= b1_hold[i - 1];
+			end
+		end
+
+endmodule