rtl/gfx: implement fragment mask clear

3 files changed, 93 insertions, 7 deletions

diff --git a/rtl/gfx/gfx.sv b/rtl/gfx/gfx.sv
index fcaaffb..f973b73 100644
--- a/rtl/gfx/gfx.sv
+++ b/rtl/gfx/gfx.sv
@@ -26,7 +26,7 @@ module gfx
 	output rgb30       scan_data
 );
 
-	logic enable_clear, swap_buffers;
+	logic enable_clear, start_clear, swap_buffers;
 	rgb24 clear_color;
 
 	gfx_cmd cmd
@@ -38,10 +38,17 @@ module gfx
 
 	gfx_masks masks
 	(
-		.frag_mask_set(0),
-		.frag_mask_write(0),
 		.frag_mask_read_addr(),
-		.frag_mask_write_addr(),
+		.*
+	);
+
+	logic frag_mask_set, frag_mask_write, frag_wait;
+	linear_coord frag_mask_write_addr;
+
+	gfx_clear clear
+	(
+		.rop_mask_addr(),
+		.rop_mask_assert(0),
 		.*
 	);
 
diff --git a/rtl/gfx/gfx_clear.sv b/rtl/gfx/gfx_clear.sv
new file mode 100644
index 0000000..ae9a20c
--- /dev/null
+++ b/rtl/gfx/gfx_clear.sv
@@ -0,0 +1,70 @@
+`include "gfx/gfx_defs.sv"
+
+module gfx_clear
+(
+	input  logic        clk,
+	                    rst_n,
+
+	input  logic        start_clear,
+
+	input  linear_coord rop_mask_addr,
+	input  logic        rop_mask_assert,
+	output logic        frag_wait,
+
+	output logic        frag_mask_set,
+	                    frag_mask_write,
+	output linear_coord frag_mask_write_addr
+);
+
+	enum int unsigned
+	{
+		FRAG,
+		CLEAR
+	} state;
+
+	logic end_clear;
+
+	assign end_clear = frag_mask_write_addr == `GFX_LINEAR_RES - 1;
+
+	always_comb
+		unique case (state)
+			FRAG:  frag_wait = start_clear;
+			CLEAR: frag_wait = 1;
+		endcase
+
+	always_ff @(posedge clk or negedge rst_n)
+		if (!rst_n) begin
+			state <= FRAG;
+			frag_mask_write <= 0;
+		end else unique case (state)
+			FRAG: begin
+				frag_mask_write <= rop_mask_assert;
+
+				if (start_clear) begin
+					state <= CLEAR;
+					frag_mask_write <= 1;
+				end
+			end
+
+			CLEAR:
+				if (end_clear) begin
+					state <= FRAG;
+					frag_mask_write <= 0;
+				end
+		endcase
+
+	always_ff @(posedge clk)
+		unique case (state)
+			FRAG: begin
+				frag_mask_set <= !start_clear;
+				frag_mask_write_addr <= rop_mask_addr;
+
+				if (start_clear)
+					frag_mask_write_addr <= 0;
+			end
+
+			CLEAR:
+				frag_mask_write_addr <= frag_mask_write_addr + 1;
+		endcase
+
+endmodule
diff --git a/rtl/gfx/gfx_cmd.sv b/rtl/gfx/gfx_cmd.sv
index 424cf5d..98845c9 100644
--- a/rtl/gfx/gfx_cmd.sv
+++ b/rtl/gfx/gfx_cmd.sv
@@ -15,13 +15,15 @@ module gfx_cmd
 
 	output logic       swap_buffers,
 	                   enable_clear,
+	                   start_clear,
 	output rgb24       clear_color
 );
 
 	struct packed
 	{
-		logic[5:0] mbz;
-		logic      enable_clear,
+		logic[4:0] mbz;
+		logic      start_frame,
+		           enable_clear,
 		           swap_buffers;
 		rgb24      clear_color;
 	} readdata_scan, writedata_scan;
@@ -36,17 +38,21 @@ module gfx_cmd
 	assign cmd_readdata = readdata_scan;
 
 	rgb24 next_clear_color;
-	logic next_enable_clear, next_swap_buffers;
+	logic next_start_clear, next_enable_clear, next_swap_buffers;
 
 	always_ff @(posedge clk or negedge rst_n)
 		if (!rst_n) begin
+			start_clear <= 0;
 			enable_clear <= 0;
 			swap_buffers <= 0;
 
+			next_start_clear <= 0;
 			next_enable_clear <= 0;
 			next_swap_buffers <= 0;
 		end else begin
+			start_clear <= 0;
 			if (vsync) begin
+				start_clear <= next_start_clear;
 				enable_clear <= next_enable_clear;
 				swap_buffers <= next_swap_buffers;
 			end
@@ -54,6 +60,9 @@ module gfx_cmd
 			if (cmd_write) begin
 				next_enable_clear <= writedata_scan.enable_clear;
 				next_swap_buffers <= writedata_scan.swap_buffers;
+
+				if (!next_start_clear)
+					next_start_clear <= writedata_scan.start_frame && writedata_scan.enable_clear;
 			end
 		end