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library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use ieee.numeric_std_unsigned.all;
-- This arbitrates fairly between two Masters connected to a single Slave
entity avm_arbit is
generic (
G_ADDRESS_SIZE : integer;
G_DATA_SIZE : integer
);
port (
clk_i : in std_logic;
rst_i : in std_logic;
-- Slave interface 0 (input)
s0_avm_write_i : in std_logic;
s0_avm_read_i : in std_logic;
s0_avm_address_i : in std_logic_vector(G_ADDRESS_SIZE-1 downto 0);
s0_avm_writedata_i : in std_logic_vector(G_DATA_SIZE-1 downto 0);
s0_avm_byteenable_i : in std_logic_vector(G_DATA_SIZE/8-1 downto 0);
s0_avm_burstcount_i : in std_logic_vector(7 downto 0);
s0_avm_readdata_o : out std_logic_vector(G_DATA_SIZE-1 downto 0);
s0_avm_readdatavalid_o : out std_logic;
s0_avm_waitrequest_o : out std_logic;
-- Slave interface 1 (input)
s1_avm_write_i : in std_logic;
s1_avm_read_i : in std_logic;
s1_avm_address_i : in std_logic_vector(G_ADDRESS_SIZE-1 downto 0);
s1_avm_writedata_i : in std_logic_vector(G_DATA_SIZE-1 downto 0);
s1_avm_byteenable_i : in std_logic_vector(G_DATA_SIZE/8-1 downto 0);
s1_avm_burstcount_i : in std_logic_vector(7 downto 0);
s1_avm_readdata_o : out std_logic_vector(G_DATA_SIZE-1 downto 0);
s1_avm_readdatavalid_o : out std_logic;
s1_avm_waitrequest_o : out std_logic;
-- Master interface (output)
m_avm_write_o : out std_logic;
m_avm_read_o : out std_logic;
m_avm_address_o : out std_logic_vector(G_ADDRESS_SIZE-1 downto 0);
m_avm_writedata_o : out std_logic_vector(G_DATA_SIZE-1 downto 0);
m_avm_byteenable_o : out std_logic_vector(G_DATA_SIZE/8-1 downto 0);
m_avm_burstcount_o : out std_logic_vector(7 downto 0);
m_avm_readdata_i : in std_logic_vector(G_DATA_SIZE-1 downto 0);
m_avm_readdatavalid_i : in std_logic;
m_avm_waitrequest_i : in std_logic
);
end entity avm_arbit;
architecture synthesis of avm_arbit is
signal s0_active_req : std_logic;
signal s1_active_req : std_logic;
signal s0_active_grant : std_logic := '0';
signal s1_active_grant : std_logic := '0';
signal active_grants : std_logic_vector(1 downto 0);
signal last_grant : std_logic := '0';
signal burstcount : std_logic_vector(7 downto 0);
begin
s0_avm_waitrequest_o <= not s0_active_grant;
s1_avm_waitrequest_o <= not s1_active_grant;
s0_active_req <= s0_avm_write_i or s0_avm_read_i;
s1_active_req <= s1_avm_write_i or s1_avm_read_i;
p_burstcount : process (clk_i)
begin
if rising_edge(clk_i) then
if burstcount = X"00" then
if s0_avm_write_i and not s0_avm_waitrequest_o then
burstcount <= s0_avm_burstcount_i;
end if;
if s1_avm_write_i and not s1_avm_waitrequest_o then
burstcount <= s1_avm_burstcount_i;
end if;
else
if (s0_avm_write_i and not s0_avm_waitrequest_o) or
s0_avm_readdatavalid_o or
(s1_avm_write_i and not s1_avm_waitrequest_o) or
s1_avm_readdatavalid_o then
burstcount <= burstcount - 1;
end if;
end if;
if rst_i = '1' then
burstcount <= X"00";
end if;
end if;
end process p_burstcount;
active_grants <= s0_active_grant & s1_active_grant;
p_grant : process (clk_i)
begin
if rising_edge(clk_i) then
case active_grants is
when "00" =>
if s0_active_req = '1' and last_grant = '1' then
s0_active_grant <= '1';
last_grant <= '1';
end if;
if s1_active_req = '1' and last_grant = '0' then
s1_active_grant <= '1';
last_grant <= '0';
end if;
when "01" =>
if burstcount = X"01" then
if (s1_avm_write_i and not s1_avm_waitrequest_o) or
s1_avm_readdatavalid_o then
s1_active_grant <= '0';
end if;
end if;
when "10" =>
if burstcount = X"01" then
if (s0_avm_write_i and not s0_avm_waitrequest_o) or
s0_avm_readdatavalid_o then
s0_active_grant <= '0';
end if;
end if;
when others =>
report "S0 and S1 both active"
severity failure;
end case;
if rst_i = '1' then
s0_active_grant <= '0';
s1_active_grant <= '0';
last_grant <= '0';
end if;
end if;
end process p_grant;
m_avm_write_o <= s0_avm_write_i when last_grant = '0' else s1_avm_write_i;
m_avm_read_o <= s0_avm_read_i when last_grant = '0' else s1_avm_read_i;
m_avm_address_o <= s0_avm_address_i when last_grant = '0' else s1_avm_address_i;
m_avm_writedata_o <= s0_avm_writedata_i when last_grant = '0' else s1_avm_writedata_i;
m_avm_byteenable_o <= s0_avm_byteenable_i when last_grant = '0' else s1_avm_byteenable_i;
m_avm_burstcount_o <= s0_avm_burstcount_i when last_grant = '0' else s1_avm_burstcount_i;
s0_avm_readdata_o <= m_avm_readdata_i;
s0_avm_readdatavalid_o <= m_avm_readdatavalid_i when last_grant = '0' else '0';
s1_avm_readdata_o <= m_avm_readdata_i;
s1_avm_readdatavalid_o <= m_avm_readdatavalid_i when last_grant = '1' else '0';
end architecture synthesis;
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