Merge pull request #235 from paulusmack/master

More instructions and a random number generator

fpga/fpga-random.vhdl

@@ -0,0 +1,53 @@
+-- Random number generator for Microwatt
+-- Based on https://pdfs.semanticscholar.org/83ac/9e9c1bb3dad5180654984604c8d5d8137412.pdf
+-- "High Speed True Random Number Generators in Xilinx FPGAs"
+-- by Catalin Baetoniu, Xilinx Inc.
+
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+library work;
+
+entity random is
+    port (
+        clk  : in std_ulogic;
+        data : out std_ulogic_vector(63 downto 0);
+        raw  : out std_ulogic_vector(63 downto 0);
+        err  : out std_ulogic
+        );
+end entity random;
+
+architecture behaviour of random is
+    signal ringosc : std_ulogic_vector(63 downto 0);
+    signal ro_reg  : std_ulogic_vector(63 downto 0);
+    signal lhca    : std_ulogic_vector(63 downto 0);
+
+    constant lhca_diag : std_ulogic_vector(63 downto 0) := x"fffffffffffffffb";
+
+begin
+    random_osc : process(all)
+    begin
+        -- chaotic set of ring oscillators
+        ringosc(0) <= ringosc(63) xor ringosc(0) xor ringosc(1);
+        for i in 1 to 62 loop
+            ringosc(i) <= ringosc(i-1) xor ringosc(i) xor ringosc(i+1);
+        end loop;
+        ringosc(63) <= not (ringosc(62) xor ringosc(63) xor ringosc(0));
+    end process;
+
+    lhca_update : process(clk)
+    begin
+        if rising_edge(clk) then
+            ro_reg <= ringosc;
+            raw <= ro_reg;
+            -- linear hybrid cellular automaton
+            -- used to even out the statistics of the ring oscillators
+            lhca <= ('0' & lhca(63 downto 1)) xor (lhca and lhca_diag) xor
+                    (lhca(62 downto 0) & '0') xor ro_reg;
+        end if;
+    end process;
+
+    data <= lhca;
+    err <= '0';
+end behaviour;

fpga/fpga-random.xdc

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+set_property ALLOW_COMBINATORIAL_LOOPS TRUE [get_nets soc0/processor/execute1_0/random_0/ro_reg*]
+set_property ALLOW_COMBINATORIAL_LOOPS TRUE [get_nets soc0/processor/execute1_0/random_0/p_*]
+set_property ALLOW_COMBINATORIAL_LOOPS TRUE [get_nets soc0/processor/execute1_0/random_0/D*]