initial

README.md

+# A basic graphics processor
+
+The processor only knows how to render a list of sprites which have a velocity.
+
+## Problems encountered
+
+- GHDL does not support external signals (https://github.com/ghdl/ghdl/issues/24). Workaround:
+  - [using global signals](https://stackoverflow.com/questions/40286725/how-can-i-get-internal-signals-to-testbench-in-vhdl-97-and-isim/40313051#40313051)
+
+## Potential questions
+
+- In a testbench you want to wait for a signal to be activated in a non-sensitivized process with `wait for` statements. What could be the problem with the following?
+
+  ```vhdl
+  wait for tlast = '1';
+  ```
+  You have to add `wait on tlast for tlast = '1'`
+  <!--TODO I have to verify this in another simulator -->
+
+- what happens if we do this after directly after reset:
+
+  ```
+  for line in frame'range loop
+  	for pixel in line'range loop
+  		pixel <= '0';
+  	end loop;
+  end loop;
+  ```
+
+## Handy resources
+
+- https://www.synthworks.com/downloads/type_pkg_quickref.pdf

ghdl.mk

+ENTITY ?= tb
+
+default: wave.gtkw wave.ghw
+
+tb.o: top.o
+
+GHDL_OPTS = --std=08
+GHDL = ghdl $(GHDL_OPTS)
+
+.PRECIOUS: wave.ghw
+wave.ghw: $(ENTITY)
+	@# ignore error in case we interrupt the sim using CTRL+C
+	-ghdl run $(GHDL_OPTS) $< --wave=$@
+
+.PHONY: gtkwave
+gtkwave: wave.gtkw
+	gtkwave $<
+
+# creates a basic gtkwave savefile which loads the ghdl wave file
+wave.gtkw:
+	$(file >$@,[dumpfile] "$<")
+
+%.o: %.vhd
+	ghdl analyze $(GHDL_OPTS) $<
+
+%: %.o
+	ghdl elaborate $(GHDL_OPTS) $(@)
+
+.PHONY: clean
+clean:
+	$(RM) *.o *.cf
+	$(RM) $(ENTITY)
+	$(RM) wave.ghw

makefile

+ghdl.mk
\ No newline at end of file

tb.vhd

+library ieee;
+use ieee.std_logic_1164.all;
+
+entity tb is
+end entity;
+
+architecture a of tb is
+	constant CLK_PERIOD : time := 10 ns;
+	constant LINE_PIXEL_COUNT: natural := 8;
+	constant LINE_COUNT: natural := 6;
+
+	signal clk: std_ulogic := '1';
+	signal rst: std_ulogic;
+	signal tlast: std_ulogic;
+begin
+	clk <= not clk after CLK_PERIOD;
+
+	duv: entity work.top
+	generic map(LINE_PIXEL_COUNT, LINE_COUNT)
+	port map(clk, rst, tlast);
+
+	process
+	begin
+		wait for 100 ns;
+		rst <= '1';
+		wait for 100 ns;
+		rst <= '0';
+		report "Waiting for tlast";
+		wait on tlast until tlast = '1';
+		report "tlast active";
+		std.env.finish;
+	end process;
+
+	timeout: process
+	begin
+		wait for 200 us;
+		report "Timeout" severity error;
+		std.env.finish;
+	end process;
+end architecture;

top.vhd

+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std_unsigned.all;
+
+entity top is
+generic (
+	LINE_PIXEL_COUNT: positive := 640;
+	LINE_COUNT: positive := 480;
+	MAX_SPRITE_COUNT: positive := 8
+);
+port (
+	clk, rst: std_ulogic;
+	--TODO axi output
+	tlast: out std_ulogic
+);
+end;
+
+architecture a of top is
+	constant MAX_VEL_X: natural := 3; 
+	constant MAX_VEL_Y: natural := 3; 
+
+	type line_t is array (0 to LINE_PIXEL_COUNT-1) of std_ulogic;
+	type frame_t is array (0 to LINE_COUNT-1) of line_t;
+	signal frame: frame_t;
+
+	type state_t is (init, run);
+	signal st: state_t;
+
+	subtype pixel_x_t is natural range 0 to LINE_PIXEL_COUNT-1;
+	subtype pixel_y_t is natural range 0 to LINE_COUNT-1;
+	signal line_pixel_ptr: pixel_x_t;
+	signal line_ptr: pixel_y_t;
+
+	type pos_vec_t is record
+		x: pixel_x_t;
+		y: pixel_y_t;
+	end record;
+	constant POS_VEC_ZERO: pos_vec_t := (0, 0);
+
+	type vel_vec_t is record
+		x: natural range 0 to MAX_VEL_X;
+		y: natural range 0 to MAX_VEL_Y;
+	end record;
+	constant VEL_VEC_ZERO: vel_vec_t := (0, 0);
+
+	type sprite_t is record
+		en: boolean;
+		pos: pos_vec_t;
+		vel: vel_vec_t;
+	end record;
+	constant SPRITE_INIT: sprite_t := (false, POS_VEC_ZERO, VEL_VEC_ZERO);
+
+	type sprites_t is array(0 to MAX_SPRITE_COUNT-1) of sprite_t;
+	constant SPRITES_INIT: sprites_t := (sprites_t'range => SPRITE_INIT);
+	signal sprites: sprites_t;
+begin
+	process (clk) is
+	begin
+		if rising_edge(clk) then
+			if rst then
+				st <= state_t'left;
+				line_ptr <= 0;
+				line_pixel_ptr <= 0;
+				tlast <= '0';
+				sprites <= SPRITES_INIT;
+			end if;
+
+			-- state transition logic
+			case st is
+			when init =>
+				frame(line_ptr)(line_pixel_ptr) <= '1';
+				if line_pixel_ptr = line_pixel_ptr'subtype'right then
+					line_pixel_ptr <= 0;
+
+					if line_ptr = line_ptr'subtype'right then
+						line_ptr <= 0;
+						tlast <= '1';
+						st <= run;
+					else
+						line_ptr <= line_ptr + 1;
+					end if;
+				else
+					line_pixel_ptr <= line_pixel_ptr + 1;
+				end if;
+
+			when run =>
+				-- TODO update sprites
+
+			end case;
+		end if;
+  end process;
+end;

wave.gtkw

+[dumpfile] "wave.ghw"
+top.tb.clk
+top.tb.rst
+top.tb.tlast
+-
+top.tb.duv.st
+top.tb.duv.line_pixel_ptr
+top.tb.duv.line_ptr
+-
+@28
+#{frame[0]} top.tb.duv.frame[0][0] top.tb.duv.frame[0][1] top.tb.duv.frame[0][2] top.tb.duv.frame[0][7]
+#{frame[1]} top.tb.duv.frame[1][0] top.tb.duv.frame[1][1] top.tb.duv.frame[1][2] top.tb.duv.frame[1][7]
+#{frame[4]} top.tb.duv.frame[4][0] top.tb.duv.frame[4][1] top.tb.duv.frame[4][2] top.tb.duv.frame[4][7]
+#{frame[5]} top.tb.duv.frame[5][0] top.tb.duv.frame[5][1] top.tb.duv.frame[5][2] top.tb.duv.frame[5][7]