fpga: ram: Use Verilog model for synthesis and VHDL for simulation

fpga/hdl/design/ram_vhdl.vhd

@@ -0,0 +1,94 @@
+-- -------------------------------------------------------------------------- --
+--              TRASHERNET SoC - A Trashy Ethernet SoC for FPGAs              --
+-- -------------------------------------------------------------------------- --
+-- Servant-compatible RAM, rewritten in VHDL
+-- -------------------------------------------------------------------------- --
+-- Author       : Markus Koch <markus@notsyncing.net>
+-- Contributors : None
+-- License      : Mozilla Public License (MPL) Version 2
+-- -------------------------------------------------------------------------- --
+
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+use std.textio.all;
+
+library generics;
+use generics.wishbone_pkg.all;
+
+entity ram_vhdl is
+	generic(
+		memfile   : string  := "data/empty.hex";
+		read_only : boolean := false;
+		adr_width : integer := 16
+	);
+	port(
+		clk  : in  std_logic;           -- CPU and bus clock
+		clr  : in  std_logic;           -- Synchronous reset
+
+		wb_o : out wishbone_slave_out;  -- Wishbone bus (out)
+		wb_i : in  wishbone_slave_in    -- Wishbone bus (in)
+	);
+end entity ram_vhdl;
+
+architecture rtl of ram_vhdl is
+	type mem_t is array (0 to 2 ** adr_width - 1) of std_logic_vector(wb_i.dat'range);
+
+	impure function init_ram_hex return mem_t is
+		file text_file       : text open read_mode is memfile;
+		variable text_line   : line;
+		variable ram_content : mem_t := (others => (others => '0'));
+	begin
+		for i in 0 to 2 ** adr_width - 1 loop
+			exit when endfile(text_file);
+			readline(text_file, text_line);
+			hread(text_line, ram_content(i));
+		end loop;
+
+		return ram_content;
+	end function;
+
+	signal mem         : mem_t := init_ram_hex;
+	signal mem_address : integer range mem'range;
+begin
+	wb_o.rty   <= '0';
+	wb_o.err   <= '0';
+	wb_o.stall <= '0';
+
+	mem_address <= to_integer(unsigned(wb_i.adr(adr_width - 1 + 2 downto 2)));
+
+	rowarn : process(clk) is
+	begin
+		if rising_edge(clk) then
+			if wb_i.cyc and wb_i.stb then
+				if (unsigned(wb_i.adr) > 2 ** adr_width - 1) then
+					report "ERROR: Out of bounds for " & ram_vhdl'path_name & " @0x" & to_hstring(wb_i.adr) severity error;
+				end if;
+				if (wb_i.we = '1' and read_only) then
+					report "ERROR: Write access to ROM @0x" & to_hstring(wb_i.adr) severity warning;
+				end if;
+			end if;
+		end if;
+	end process rowarn;
+
+	mem_p : process(clk) is
+	begin
+		if rising_edge(clk) then
+			wb_o.dat <= mem(mem_address);
+			wb_o.ack <= wb_i.stb;
+			if (wb_i.we) then
+				wb_o.dat <= (others => '-');
+				for i in wb_i.sel'range loop
+					if wb_i.sel(i) then
+						mem(mem_address)((i + 1) * 8 - 1 downto (i * 8)) <= wb_i.dat((i + 1) * 8 - 1 downto (i * 8));
+					end if;
+				end loop;
+			end if;
+
+			if clr then
+				wb_o.dat <= (others => '-');
+				wb_o.ack <= '0';
+			end if;
+		end if;
+	end process mem_p;
+end architecture rtl;

fpga/hdl/design/servant_ram.vhd

@@ -1,7 +1,7 @@
 -- -------------------------------------------------------------------------- --
 --              TRASHERNET SoC - A Trashy Ethernet SoC for FPGAs              --
 -- -------------------------------------------------------------------------- --
--- Servant-compatible RAM, rewritten in VHDL
+-- TODO
 -- -------------------------------------------------------------------------- --
 -- Author       : Markus Koch <markus@notsyncing.net>
 -- Contributors : None
@@ -11,7 +11,6 @@
 library ieee;
 use ieee.std_logic_1164.all;
 use ieee.numeric_std.all;
-use std.textio.all;
 
 library generics;
 use generics.wishbone_pkg.all;
@@ -20,7 +19,8 @@ entity servant_ram_vhdl is
 	generic(
 		memfile    : string  := "data/empty.hex";
 		read_only  : boolean := false;
-		adr_width : integer := 16
+		adr_width  : integer := 16;
+		force_vlog : boolean := false
 	);
 	port(
 		clk  : in  std_logic;           -- CPU and bus clock
@@ -32,31 +32,49 @@ entity servant_ram_vhdl is
 end entity servant_ram_vhdl;
 
 architecture rtl of servant_ram_vhdl is
-	type mem_t is array (0 to 2 ** adr_width - 1) of std_logic_vector(wb_i.dat'range);
+	component servant_ram
+		generic(
+			depth   : integer;
+			aw      : integer;
+			memfile : string
+		);
+		port(
+			i_wb_clk : in  std_logic;
+			i_wb_rst : in  std_logic;
+			i_wb_adr : in  std_logic_vector;
+			i_wb_dat : in  std_logic_vector;
+			i_wb_sel : in  std_logic_vector;
+			i_wb_we  : in  std_logic;
+			i_wb_cyc : in  std_logic;
+			o_wb_rdt : out std_logic_vector;
+			o_wb_ack : out std_logic
+		);
+	end component servant_ram;
 
-	impure function init_ram_hex return mem_t is
-		file text_file       : text open read_mode is memfile;
-		variable text_line   : line;
-		variable ram_content : mem_t := (others => (others => '0'));
-	begin
-		for i in 0 to 2 ** adr_width - 1 loop
-			exit when endfile(text_file);
-			readline(text_file, text_line);
-			hread(text_line, ram_content(i));
-		end loop;
-
-		return ram_content;
-	end function;
-
-	signal mem         : mem_t := init_ram_hex;
-	signal mem_address : integer range mem'range;
 begin
+	vlogforce : if force_vlog generate
+		servant_ram_inst : component servant_ram
+			generic map(
+				depth   => 2 ** adr_width,
+				aw      => adr_width,
+				memfile => memfile
+			)
+			port map(
+				i_wb_clk => clk,
+				i_wb_rst => clr,
+				i_wb_adr => wb_i.adr(adr_width - 1 downto 2),
+				i_wb_dat => wb_i.dat,
+				i_wb_sel => wb_i.sel,
+				i_wb_we  => wb_i.we,
+				i_wb_cyc => wb_i.cyc and wb_i.stb,
+				o_wb_rdt => wb_o.dat,
+				o_wb_ack => wb_o.ack
+			);
+
 		wb_o.rty   <= '0';
 		wb_o.err   <= '0';
 		wb_o.stall <= '0';
 
-	mem_address <= to_integer(unsigned(wb_i.adr(adr_width - 1 + 2 downto 2)));
-
 		rowarn : process(clk) is
 		begin
 			if rising_edge(clk) then
@@ -71,24 +89,18 @@ begin
 			end if;
 		end process rowarn;
 
-	mem_p : process(clk) is
+	else generate
-	begin
+		ram_vhdl_inst : entity work.ram_vhdl
-		if rising_edge(clk) then
+			generic map(
-			wb_o.dat <= mem(mem_address);
+				memfile   => memfile,
-			wb_o.ack <= wb_i.stb;
+				read_only => read_only,
-			if (wb_i.we) then
+				adr_width => adr_width
-				wb_o.dat <= (others => '-');
+			)
-				for i in wb_i.sel'range loop
+			port map(
-					if wb_i.sel(i) then
+				clk  => clk,
-						mem(mem_address)((i + 1) * 8 - 1 downto (i * 8)) <= wb_i.dat((i + 1) * 8 - 1 downto (i * 8));
+				clr  => clr,
-					end if;
+				wb_o => wb_o,
-				end loop;
+				wb_i => wb_i
-			end if;
+			);
-
+	end generate vlogforce;
-			if clr then
-				wb_o.dat <= (others => '-');
-				wb_o.ack <= '0';
-			end if;
-		end if;
-	end process mem_p;
 end architecture rtl;

fpga/hdl/design/top.vhd

@@ -239,7 +239,8 @@ begin
 		generic map(
 			memfile   => "../sw/bootrom/bootrom.vhex",
 			read_only => true,
-			adr_width => 9
+			adr_width => 9,
+			force_vlog  => not in_simulation -- GHDL + Yosys doesn't keep the memfile
 		)
 		port map(
 			clk  => clk,