trashernet-soc/fpga/hdl/design/ram_vhdl.vhd

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-- -------------------------------------------------------------------------- --
-- 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;