rtl/gfx: implement double-buffered scanout

1 files changed, 53 insertions, 0 deletions

diff --git a/rtl/gfx/gfx_masks.sv b/rtl/gfx/gfx_masks.sv
new file mode 100644
index 0000000..86d1b78
--- /dev/null
+++ b/rtl/gfx/gfx_masks.sv
@@ -0,0 +1,53 @@
+`include "gfx/gfx_defs.sv"
+
+module gfx_masks
+(
+	input  logic        clk,
+
+	input  logic        swap_buffers,
+
+	input  linear_coord scan_mask_addr,
+	output logic        scan_mask,
+
+	input  logic        frag_mask_write,
+	                    frag_mask_set,
+	input  linear_coord frag_mask_read_addr,
+	                    frag_mask_write_addr,
+	output logic        frag_mask
+);
+
+	logic mask_a, mask_b, frag_write_hold, frag_set_hold;
+	linear_coord scan_addr_hold, frag_write_addr_hold, frag_read_addr_hold;
+
+	gfx_mask_sram sram_a
+	(
+		.set(frag_set_hold),
+		.mask(mask_a),
+		.write(swap_buffers && frag_write_hold),
+		.read_addr(swap_buffers ? frag_read_addr_hold : scan_addr_hold),
+		.write_addr(frag_write_addr_hold),
+		.*
+	);
+
+	gfx_mask_sram sram_b
+	(
+		.set(frag_set_hold),
+		.mask(mask_b),
+		.write(!swap_buffers && frag_write_hold),
+		.read_addr(swap_buffers ? scan_addr_hold : frag_read_addr_hold),
+		.write_addr(frag_write_addr_hold),
+		.*
+	);
+
+	always_ff @(posedge clk) begin
+		scan_mask <= swap_buffers ? mask_b : mask_a;
+		scan_addr_hold <= scan_mask_addr;
+
+		frag_mask <= swap_buffers ? mask_a : mask_b;
+		frag_set_hold <= frag_mask_set;
+		frag_write_hold <= frag_mask_write;
+		frag_read_addr_hold <= frag_mask_read_addr;
+		frag_write_addr_hold <= frag_mask_write_addr;
+	end
+
+endmodule