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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_sys_timer.vhd] - Rev 242
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-- Copyright (c)2006, 2016, 2019, 2020 Jeremy Seth Henry -- All rights reserved. -- -- Redistribution and use in source and binary forms, with or without -- modification, are permitted provided that the following conditions are met: -- * Redistributions of source code must retain the above copyright -- notice, this list of conditions and the following disclaimer. -- * 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, -- where applicable (as part of a user interface, debugging port, etc.) -- -- THIS SOFTWARE IS PROVIDED BY JEREMY SETH HENRY ``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 JEREMY SETH HENRY 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. -- -- VHDL Units : o8_sys_timer -- Description: Provides an 8-bit microsecond resolution timer for generating -- : periodic interrupts for the Open8 CPU. -- -- Notes : It is possible to set the value to zero, resulting in the -- : output staying high indefinitely. This may cause an issue if -- : the output is connected to an interrupt input. -- : Also provides uSec_Tick as an output -- -- Revision History -- Author Date Change ------------------ -------- --------------------------------------------------- -- Seth Henry 07/28/11 Design Start -- Seth Henry 12/19/19 Renamed Tmr_Out to Interrupt -- Seth Henry 04/09/20 Modified timer update logic to reset the timer on -- interval write. -- Seth Henry 04/16/20 Modified to use Open8 bus record library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_unsigned.all; use ieee.std_logic_arith.all; use ieee.std_logic_misc.all; library work; use work.open8_pkg.all; entity o8_sys_timer is generic( Write_Protect : boolean := FALSE; Address : ADDRESS_TYPE ); port( Open8_Bus : in OPEN8_BUS_TYPE; Rd_Data : out DATA_TYPE; Interrupt : out std_logic ); end entity; architecture behave of o8_sys_timer is alias Clock is Open8_Bus.Clock; alias Reset is Open8_Bus.Reset; alias uSec_Tick is Open8_Bus.uSec_Tick; alias ISR_En is Open8_Bus.GP_Flags(EXT_ISR); signal Wr_En_d : std_logic; signal Rd_En_d : std_logic; alias Wr_Data is Open8_Bus.Wr_Data; constant User_Addr : ADDRESS_TYPE := Address; alias Comp_Addr is Open8_Bus.Address(15 downto 0); signal Addr_Match : std_logic := '0'; signal Wr_En : std_logic := '0'; signal Wr_Data_q : DATA_TYPE := x"00"; signal Rd_En : std_logic := '0'; signal Rd_En_q : std_logic := '0'; signal Interval : DATA_TYPE := x"00"; signal Update_Interval : std_logic; signal Timer_Cnt : DATA_TYPE := x"00"; begin Addr_Match <= '1' when Comp_Addr = User_Addr else '0'; -- If the Write_Protect generic is set only allow the memory to be written -- if the ISR bit is set. Otherwise, the memory should be read-only Write_Protect_On : if( Write_Protect )generate Wr_En_d <= Addr_Match and Open8_Bus.Wr_En and ISR_En; end generate; Write_Protect_Off : if( not Write_Protect )generate Wr_En_d <= Addr_Match and Open8_Bus.Wr_En; end generate; Rd_En_d <= Addr_Match and Open8_Bus.Rd_En; io_reg: process( Clock, Reset ) begin if( Reset = Reset_Level )then Wr_En <= '0'; Wr_Data_q <= x"00"; Rd_En <= '0'; Rd_Data <= OPEN8_NULLBUS; Interval <= x"00"; Update_Interval <= '0'; elsif( rising_edge( Clock ) )then Wr_En <= Wr_En_d; Wr_Data_q <= Wr_Data; Update_Interval <= Wr_En; if( Wr_En = '1' )then Interval <= Wr_Data_q; end if; Rd_Data <= (others => '0'); Rd_En <= Rd_En_d; if( Rd_En = '1' )then Rd_Data <= Interval; end if; end if; end process; Interval_proc: process( Clock, Reset ) begin if( Reset = Reset_Level )then Timer_Cnt <= x"00"; Interrupt <= '0'; elsif( rising_edge(Clock) )then Interrupt <= '0'; Timer_Cnt <= Timer_Cnt - uSec_Tick; if( Update_Interval = '1' )then Timer_Cnt <= Interval; elsif( or_reduce(Timer_Cnt) = '0' )then Timer_Cnt <= Interval; Interrupt <= or_reduce(Interval); -- Only trigger on Int > 0 end if; end if; end process; end architecture;
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