rtl/gfx: implement scanout command interface

1 files changed, 68 insertions, 0 deletions

diff --git a/rtl/gfx/gfx_cmd.sv b/rtl/gfx/gfx_cmd.sv
new file mode 100644
index 0000000..424cf5d
--- /dev/null
+++ b/rtl/gfx/gfx_cmd.sv
@@ -0,0 +1,68 @@
+`include "gfx/gfx_defs.sv"
+
+module gfx_cmd
+(
+	input  logic       clk,
+	                   rst_n,
+
+	input  logic[5:0]  cmd_address,
+	input  logic       cmd_read,
+	                   cmd_write,
+	input  logic[31:0] cmd_writedata,
+	output logic[31:0] cmd_readdata,
+
+	input  logic       vsync,
+
+	output logic       swap_buffers,
+	                   enable_clear,
+	output rgb24       clear_color
+);
+
+	struct packed
+	{
+		logic[5:0] mbz;
+		logic      enable_clear,
+		           swap_buffers;
+		rgb24      clear_color;
+	} readdata_scan, writedata_scan;
+
+	assign readdata_scan.clear_color = clear_color;
+	assign readdata_scan.mbz = 0;
+	assign readdata_scan.enable_clear = enable_clear;
+	assign readdata_scan.swap_buffers = swap_buffers;
+
+	assign writedata_scan = cmd_writedata;
+
+	assign cmd_readdata = readdata_scan;
+
+	rgb24 next_clear_color;
+	logic next_enable_clear, next_swap_buffers;
+
+	always_ff @(posedge clk or negedge rst_n)
+		if (!rst_n) begin
+			enable_clear <= 0;
+			swap_buffers <= 0;
+
+			next_enable_clear <= 0;
+			next_swap_buffers <= 0;
+		end else begin
+			if (vsync) begin
+				enable_clear <= next_enable_clear;
+				swap_buffers <= next_swap_buffers;
+			end
+
+			if (cmd_write) begin
+				next_enable_clear <= writedata_scan.enable_clear;
+				next_swap_buffers <= writedata_scan.swap_buffers;
+			end
+		end
+
+	always_ff @(posedge clk) begin
+		if (vsync)
+			clear_color <= next_clear_color;
+
+		if (cmd_write)
+			next_clear_color <= writedata_scan.clear_color;
+	end
+
+endmodule