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[/] [neorv32/] [trunk/] [rtl/] [core/] [neorv32_busswitch.vhd] - Rev 25
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-- ################################################################################################# -- # << NEORV32 - Bus Switch >> # -- # ********************************************************************************************* # -- # Allows to access a single peripheral bus ("p_bus") by two controller busses. Controller port # -- # A ("ca_bus") has priority over controller port B ("cb_bus"). # -- # ********************************************************************************************* # -- # BSD 3-Clause License # -- # # -- # Copyright (c) 2020, Stephan Nolting. All rights reserved. # -- # # -- # Redistribution and use in source and binary forms, with or without modification, are # -- # permitted provided that the following conditions are met: # -- # # -- # 1. Redistributions of source code must retain the above copyright notice, this list of # -- # conditions and the following disclaimer. # -- # # -- # 2. Redistributions in binary form must reproduce the above copyright notice, this list of # -- # conditions and the following disclaimer in the documentation and/or other materials # -- # provided with the distribution. # -- # # -- # 3. Neither the name of the copyright holder nor the names of its contributors may be used to # -- # endorse or promote products derived from this software without specific prior written # -- # permission. # -- # # -- # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS # -- # OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF # -- # MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE # -- # COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, # -- # EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE # -- # GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED # -- # AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING # -- # NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED # -- # OF THE POSSIBILITY OF SUCH DAMAGE. # -- # ********************************************************************************************* # -- # The NEORV32 Processor - https://github.com/stnolting/neorv32 (c) Stephan Nolting # -- ################################################################################################# library ieee; use ieee.std_logic_1164.all; use ieee.numeric_std.all; library neorv32; use neorv32.neorv32_package.all; entity neorv32_busswitch is generic ( PORT_CA_READ_ONLY : boolean := false; -- set if controller port A is read-only PORT_CB_READ_ONLY : boolean := false -- set if controller port B is read-only ); port ( -- global control -- clk_i : in std_ulogic; -- global clock, rising edge rstn_i : in std_ulogic; -- global reset, low-active, async -- controller interface a -- ca_bus_addr_i : in std_ulogic_vector(data_width_c-1 downto 0); -- bus access address ca_bus_rdata_o : out std_ulogic_vector(data_width_c-1 downto 0); -- bus read data ca_bus_wdata_i : in std_ulogic_vector(data_width_c-1 downto 0); -- bus write data ca_bus_ben_i : in std_ulogic_vector(03 downto 0); -- byte enable ca_bus_we_i : in std_ulogic; -- write enable ca_bus_re_i : in std_ulogic; -- read enable ca_bus_cancel_i : in std_ulogic; -- cancel current bus transaction ca_bus_ack_o : out std_ulogic; -- bus transfer acknowledge ca_bus_err_o : out std_ulogic; -- bus transfer error -- controller interface b -- cb_bus_addr_i : in std_ulogic_vector(data_width_c-1 downto 0); -- bus access address cb_bus_rdata_o : out std_ulogic_vector(data_width_c-1 downto 0); -- bus read data cb_bus_wdata_i : in std_ulogic_vector(data_width_c-1 downto 0); -- bus write data cb_bus_ben_i : in std_ulogic_vector(03 downto 0); -- byte enable cb_bus_we_i : in std_ulogic; -- write enable cb_bus_re_i : in std_ulogic; -- read enable cb_bus_cancel_i : in std_ulogic; -- cancel current bus transaction cb_bus_ack_o : out std_ulogic; -- bus transfer acknowledge cb_bus_err_o : out std_ulogic; -- bus transfer error -- peripheral bus -- p_bus_addr_o : out std_ulogic_vector(data_width_c-1 downto 0); -- bus access address p_bus_rdata_i : in std_ulogic_vector(data_width_c-1 downto 0); -- bus read data p_bus_wdata_o : out std_ulogic_vector(data_width_c-1 downto 0); -- bus write data p_bus_ben_o : out std_ulogic_vector(03 downto 0); -- byte enable p_bus_we_o : out std_ulogic; -- write enable p_bus_re_o : out std_ulogic; -- read enable p_bus_cancel_o : out std_ulogic; -- cancel current bus transaction p_bus_ack_i : in std_ulogic; -- bus transfer acknowledge p_bus_err_i : in std_ulogic -- bus transfer error ); end neorv32_busswitch; architecture neorv32_busswitch_rtl of neorv32_busswitch is -- access buffer -- signal ca_rd_req_buf : std_ulogic; signal ca_wr_req_buf : std_ulogic; signal cb_rd_req_buf : std_ulogic; signal cb_wr_req_buf : std_ulogic; -- access requests -- signal ca_req_current : std_ulogic; signal cb_req_current : std_ulogic; signal ca_req_buffered : std_ulogic; signal cb_req_buffered : std_ulogic; -- internal bus lines -- signal ca_bus_ack : std_ulogic; signal cb_bus_ack : std_ulogic; signal ca_bus_err : std_ulogic; signal cb_bus_err : std_ulogic; signal p_bus_we : std_ulogic; signal p_bus_re : std_ulogic; -- access arbiter -- type arbiter_state_t is (IDLE, BUSY, RETIRE, BUSY_SWITCHED, RETIRE_SWITCHED); type arbiter_t is record state : arbiter_state_t; state_nxt : arbiter_state_t; bus_sel : std_ulogic; re_trig : std_ulogic; we_trig : std_ulogic; end record; signal arbiter : arbiter_t; begin -- Access Buffer -------------------------------------------------------------------------- -- ------------------------------------------------------------------------------------------- access_buffer: process(rstn_i, clk_i) begin if (rstn_i = '0') then ca_rd_req_buf <= '0'; ca_wr_req_buf <= '0'; cb_rd_req_buf <= '0'; cb_wr_req_buf <= '0'; elsif rising_edge(clk_i) then -- controller A requests -- if (ca_rd_req_buf = '0') and (ca_wr_req_buf = '0') then -- idle ca_rd_req_buf <= ca_bus_re_i; ca_wr_req_buf <= ca_bus_we_i; elsif (ca_bus_cancel_i = '1') or -- controller cancels access (ca_bus_err = '1') or -- peripheral cancels access (ca_bus_ack = '1') then -- normal termination ca_rd_req_buf <= '0'; ca_wr_req_buf <= '0'; end if; -- controller B requests -- if (cb_rd_req_buf = '0') and (cb_wr_req_buf = '0') then cb_rd_req_buf <= cb_bus_re_i; cb_wr_req_buf <= cb_bus_we_i; elsif (cb_bus_cancel_i = '1') or -- controller cancels access (cb_bus_err = '1') or -- peripheral cancels access (cb_bus_ack = '1') then -- normal termination cb_rd_req_buf <= '0'; cb_wr_req_buf <= '0'; end if; end if; end process access_buffer; -- any current requests? -- ca_req_current <= (ca_bus_re_i or ca_bus_we_i) when (PORT_CA_READ_ONLY = false) else ca_bus_re_i; cb_req_current <= (cb_bus_re_i or cb_bus_we_i) when (PORT_CB_READ_ONLY = false) else cb_bus_re_i; -- any buffered requests? -- ca_req_buffered <= (ca_rd_req_buf or ca_wr_req_buf) when (PORT_CA_READ_ONLY = false) else ca_rd_req_buf; cb_req_buffered <= (cb_rd_req_buf or cb_wr_req_buf) when (PORT_CB_READ_ONLY = false) else cb_rd_req_buf; -- Access Arbiter Sync -------------------------------------------------------------------- -- ------------------------------------------------------------------------------------------- -- for registers that require a specific reset state -- arbiter_sync: process(rstn_i, clk_i) begin if (rstn_i = '0') then arbiter.state <= IDLE; elsif rising_edge(clk_i) then arbiter.state <= arbiter.state_nxt; end if; end process arbiter_sync; -- Peripheral Bus Arbiter ----------------------------------------------------------------- -- ------------------------------------------------------------------------------------------- arbiter_comb: process(arbiter, ca_req_current, cb_req_current, ca_req_buffered, cb_req_buffered, ca_rd_req_buf, ca_wr_req_buf, cb_rd_req_buf, cb_wr_req_buf, ca_bus_cancel_i, cb_bus_cancel_i, p_bus_ack_i, p_bus_err_i) begin -- arbiter defaults -- arbiter.state_nxt <= arbiter.state; arbiter.bus_sel <= '0'; arbiter.we_trig <= '0'; arbiter.re_trig <= '0'; -- state machine -- case arbiter.state is when IDLE => -- Controller a has full bus access -- ------------------------------------------------------------ if (ca_req_current = '1') then -- current request? arbiter.bus_sel <= '0'; arbiter.state_nxt <= BUSY; elsif (ca_req_buffered = '1') then -- buffered request? arbiter.bus_sel <= '0'; arbiter.state_nxt <= RETIRE; elsif (cb_req_current = '1') then -- current request from controller b? arbiter.bus_sel <= '1'; arbiter.state_nxt <= BUSY_SWITCHED; elsif (cb_req_buffered = '1') then -- buffered request from controller b? arbiter.bus_sel <= '1'; arbiter.state_nxt <= RETIRE_SWITCHED; end if; when BUSY => -- transaction in progress -- ------------------------------------------------------------ arbiter.bus_sel <= '0'; if (ca_bus_cancel_i = '1') or -- controller cancels access (p_bus_err_i = '1') or -- peripheral cancels access (p_bus_ack_i = '1') then -- normal termination arbiter.state_nxt <= IDLE; end if; when RETIRE => -- retire pending access -- ------------------------------------------------------------ arbiter.bus_sel <= '0'; if (PORT_CA_READ_ONLY = false) then arbiter.we_trig <= ca_wr_req_buf; end if; arbiter.re_trig <= ca_rd_req_buf; arbiter.state_nxt <= BUSY; when BUSY_SWITCHED => -- switched transaction in progress -- ------------------------------------------------------------ arbiter.bus_sel <= '1'; if (cb_bus_cancel_i = '1') or -- controller cancels access (p_bus_err_i = '1') or -- peripheral cancels access (p_bus_ack_i = '1') then -- normal termination arbiter.state_nxt <= IDLE; end if; when RETIRE_SWITCHED => -- retire pending switched access -- ------------------------------------------------------------ arbiter.bus_sel <= '1'; if (PORT_CB_READ_ONLY = false) then arbiter.we_trig <= cb_wr_req_buf; end if; arbiter.re_trig <= cb_rd_req_buf; arbiter.state_nxt <= BUSY_SWITCHED; end case; end process arbiter_comb; -- Peripheral Bus Switch ------------------------------------------------------------------ -- ------------------------------------------------------------------------------------------- p_bus_addr_o <= ca_bus_addr_i when (arbiter.bus_sel = '0') else cb_bus_addr_i; p_bus_wdata_o <= cb_bus_wdata_i when (PORT_CA_READ_ONLY = true) else ca_bus_wdata_i when (PORT_CB_READ_ONLY = true) else ca_bus_wdata_i when (arbiter.bus_sel = '0') else cb_bus_wdata_i; p_bus_ben_o <= cb_bus_ben_i when (PORT_CA_READ_ONLY = true) else ca_bus_ben_i when (PORT_CB_READ_ONLY = true) else ca_bus_ben_i when (arbiter.bus_sel = '0') else cb_bus_ben_i; p_bus_we <= ca_bus_we_i when (arbiter.bus_sel = '0') else cb_bus_we_i; p_bus_re <= ca_bus_re_i when (arbiter.bus_sel = '0') else cb_bus_re_i; p_bus_cancel_o <= ca_bus_cancel_i when (arbiter.bus_sel = '0') else cb_bus_cancel_i; p_bus_we_o <= (p_bus_we or arbiter.we_trig); p_bus_re_o <= (p_bus_re or arbiter.re_trig); ca_bus_rdata_o <= p_bus_rdata_i; cb_bus_rdata_o <= p_bus_rdata_i; ca_bus_ack <= p_bus_ack_i and (not arbiter.bus_sel); cb_bus_ack <= p_bus_ack_i and ( arbiter.bus_sel); ca_bus_ack_o <= ca_bus_ack; cb_bus_ack_o <= cb_bus_ack; ca_bus_err <= p_bus_err_i and (not arbiter.bus_sel); cb_bus_err <= p_bus_err_i and ( arbiter.bus_sel); ca_bus_err_o <= ca_bus_err; cb_bus_err_o <= cb_bus_err; end neorv32_busswitch_rtl;
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