URL
https://opencores.org/ocsvn/open8_urisc/open8_urisc/trunk
Subversion Repositories open8_urisc
[/] [open8_urisc/] [trunk/] [VHDL/] [async_ser_tx.vhd] - Rev 264
Go to most recent revision | Compare with Previous | Blame | View Log
-- Copyright (c)2006, 2016, 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 : async_ser_tx -- Description: Asynchronous transmitter wired for 8[N/E/O]1 data. Parity mode -- and bit rate are set with generics. -- -- Note: The baud rate generator will produce an approximate frequency. The -- final bit rate should be within +/- 1% of the true bit rate to -- ensure the receiver can successfully receive. With a sufficiently -- high core clock, this is generally achievable for common PC serial -- data rates. -- -- Revision History -- Author Date Change ------------------ -------- --------------------------------------------------- -- Seth Henry 04/14/20 Code cleanup and revision section added 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; entity async_ser_tx is generic( Reset_Level : std_logic; Enable_Parity : boolean; Parity_Odd_Even_n : std_logic; Clock_Divider : integer ); port( Clock : in std_logic; Reset : in std_logic; -- Tx_Data : in std_logic_vector(7 downto 0); Tx_Valid : in std_logic; -- Tx_Out : out std_logic; Tx_Done : out std_logic ); end entity; architecture behave of async_ser_tx is -- The ceil_log2 function returns the minimum register width required to -- hold the supplied integer. function ceil_log2 (x : in natural) return natural is variable retval : natural; begin retval := 1; while ((2**retval) - 1) < x loop retval := retval + 1; end loop; return retval; end ceil_log2; constant Tick_Base : integer := Clock_Divider - 1; constant Tick_Bits : integer := ceil_log2(Tick_Base); constant TICK_DIV : std_logic_vector(Tick_Bits - 1 downto 0) := conv_std_logic_vector(Tick_Base, Tick_Bits); signal Tick_Cntr : std_logic_vector(Tick_Bits - 1 downto 0) := (others => '0'); signal Tick_Trig : std_logic := '0'; signal Tx_Enable : std_logic := '0'; signal Tx_Buffer : std_logic_vector(7 downto 0) := x"00"; signal Tx_Parity : std_logic := '0'; signal Tx_State : std_logic_vector(3 downto 0) := x"0"; alias Tx_Bit_Sel is Tx_State(2 downto 0); -- State machine definitions constant IO_RSV0 : std_logic_vector(3 downto 0) := "1011"; -- B constant IO_RSV1 : std_logic_vector(3 downto 0) := "1100"; -- C constant IO_RSV2 : std_logic_vector(3 downto 0) := "1101"; -- D constant IO_IDLE : std_logic_vector(3 downto 0) := "1110"; -- E constant IO_STRT : std_logic_vector(3 downto 0) := "1111"; -- F constant IO_BIT0 : std_logic_vector(3 downto 0) := "0000"; -- 0 constant IO_BIT1 : std_logic_vector(3 downto 0) := "0001"; -- 1 constant IO_BIT2 : std_logic_vector(3 downto 0) := "0010"; -- 2 constant IO_BIT3 : std_logic_vector(3 downto 0) := "0011"; -- 3 constant IO_BIT4 : std_logic_vector(3 downto 0) := "0100"; -- 4 constant IO_BIT5 : std_logic_vector(3 downto 0) := "0101"; -- 5 constant IO_BIT6 : std_logic_vector(3 downto 0) := "0110"; -- 6 constant IO_BIT7 : std_logic_vector(3 downto 0) := "0111"; -- 7 constant IO_PARI : std_logic_vector(3 downto 0) := "1000"; -- 8 constant IO_STOP : std_logic_vector(3 downto 0) := "1001"; -- 9 constant IO_DONE : std_logic_vector(3 downto 0) := "1010"; -- A begin UART_Regs: process( Clock, Reset ) begin if( Reset = Reset_Level )then Tick_Cntr <= (others => '0'); Tick_Trig <= '0'; Tx_State <= IO_IDLE; Tx_Enable <= '0'; Tx_Buffer <= (others => '0'); if( Enable_Parity )then Tx_Parity <= '0'; end if; Tx_Out <= '1'; Tx_Done <= '0'; elsif( rising_edge(Clock) )then Tick_Cntr <= (others => '0'); Tick_Trig <= '0'; if( Tx_Enable = '1' )then Tick_Cntr <= Tick_Cntr - 1; Tick_Trig <= '0'; if( or_reduce(Tick_Cntr) = '0' )then Tick_Cntr <= TICK_DIV; Tick_Trig <= '1'; end if; end if; if( Tx_Valid = '1' )then Tx_Buffer <= Tx_Data; Tx_Enable <= '1'; end if; Tx_State <= Tx_State + Tick_Trig; Tx_Done <= '0'; Tx_Out <= '1'; case( Tx_State )is when IO_IDLE => if( Enable_Parity )then Tx_Parity <= Parity_Odd_Even_n; end if; when IO_STRT => Tx_Out <= '0'; when IO_BIT0 | IO_BIT1 | IO_BIT2 | IO_BIT3 | IO_BIT4 | IO_BIT5 | IO_BIT6 | IO_BIT7 => Tx_Out <= Tx_Buffer(conv_integer(Tx_Bit_Sel)); if( Tick_Trig = '1' and Enable_Parity )then Tx_Parity <= Tx_Parity xor Tx_Buffer(conv_integer(Tx_Bit_Sel)); end if; when IO_PARI => if( Enable_Parity )then Tx_Out <= Tx_Parity; end if; when IO_STOP => when IO_DONE => Tx_Done <= '1'; Tx_Enable <= '0'; Tx_State <= IO_IDLE; when others => end case; if( Tx_Enable = '0' )then Tx_State <= IO_IDLE; end if; end if; end process; end architecture;
Go to most recent revision | Compare with Previous | Blame | View Log