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microwatt/wishbone_arbiter.vhdl

83 lines
2.1 KiB
VHDL

library ieee;
use ieee.std_logic_1164.all;
library work;
use work.wishbone_types.all;
-- TODO: Use an array of master/slaves with parametric size
entity wishbone_arbiter is
port (clk : in std_ulogic;
rst : in std_ulogic;
wb1_in : in wishbone_master_out;
wb1_out : out wishbone_slave_out;
wb2_in : in wishbone_master_out;
wb2_out : out wishbone_slave_out;
wb3_in : in wishbone_master_out;
wb3_out : out wishbone_slave_out;
wb_out : out wishbone_master_out;
wb_in : in wishbone_slave_out
);
end wishbone_arbiter;
architecture behave of wishbone_arbiter is
type wishbone_arbiter_state_t is (IDLE, WB1_BUSY, WB2_BUSY, WB3_BUSY);
signal state : wishbone_arbiter_state_t := IDLE;
begin
wishbone_muxes: process(state, wb_in, wb1_in, wb2_in, wb3_in)
begin
-- Requests from masters are fully muxed
wb_out <= wb1_in when state = WB1_BUSY else
wb2_in when state = WB2_BUSY else
wb3_in when state = WB3_BUSY else
wishbone_master_out_init;
-- Responses from slave don't need to mux the data bus
wb1_out.dat <= wb_in.dat;
wb2_out.dat <= wb_in.dat;
wb3_out.dat <= wb_in.dat;
wb1_out.ack <= wb_in.ack when state = WB1_BUSY else '0';
wb2_out.ack <= wb_in.ack when state = WB2_BUSY else '0';
wb3_out.ack <= wb_in.ack when state = WB3_BUSY else '0';
wb1_out.stall <= wb_in.stall when state = WB1_BUSY else '1';
wb2_out.stall <= wb_in.stall when state = WB2_BUSY else '1';
wb3_out.stall <= wb_in.stall when state = WB3_BUSY else '1';
end process;
wishbone_arbiter_process: process(clk)
begin
if rising_edge(clk) then
if rst = '1' then
state <= IDLE;
else
case state is
when IDLE =>
if wb1_in.cyc = '1' then
state <= WB1_BUSY;
elsif wb2_in.cyc = '1' then
state <= WB2_BUSY;
elsif wb3_in.cyc = '1' then
state <= WB3_BUSY;
end if;
when WB1_BUSY =>
if wb1_in.cyc = '0' then
state <= IDLE;
end if;
when WB2_BUSY =>
if wb2_in.cyc = '0' then
state <= IDLE;
end if;
when WB3_BUSY =>
if wb3_in.cyc = '0' then
state <= IDLE;
end if;
end case;
end if;
end if;
end process;
end behave;