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---------------------------------------------------------------------------------------------------
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-- Filename : usbrx_ssc.vhd
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-- Project : OsmoSDR FPGA Firmware
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-- Purpose : ATSAM3U SSC Interface
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---------------------------------------------------------------------------------------------------
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-----------------------------------------------------------------------------------
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-- Copyright (C) 2012 maintech GmbH, Otto-Hahn-Str. 15, 97204 Hoechberg, Germany --
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-- written by Matthias Kleffel --
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-- --
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-- This program is free software; you can redistribute it and/or modify --
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-- it under the terms of the GNU General Public License as published by --
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-- the Free Software Foundation as version 3 of the License, or --
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-- --
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-- This program is distributed in the hope that it will be useful, --
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-- but WITHOUT ANY WARRANTY; without even the implied warranty of --
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-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the --
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-- GNU General Public License V3 for more details. --
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-- --
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-- You should have received a copy of the GNU General Public License --
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-- along with this program. If not, see <http://www.gnu.org/licenses/>. --
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-----------------------------------------------------------------------------------
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library ieee;
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use ieee.std_logic_1164.all;
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use ieee.numeric_std.all;
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library work;
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use work.all;
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use work.mt_toolbox.all;
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use work.usbrx.all;
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entity usbrx_ssc is
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port(
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-- common
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clk : in std_logic;
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reset : in std_logic;
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-- config
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config : in usbrx_ssc_config_t;
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-- output
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in_clk : in std_logic;
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in_i : in signed(15 downto 0);
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in_q : in signed(15 downto 0);
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-- SSC interface
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ssc_clk : out std_logic;
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ssc_syn : out std_logic;
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ssc_dat : out std_logic
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);
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end usbrx_ssc;
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architecture rtl of usbrx_ssc is
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-- CLK generator
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signal cg_div : unsigned(7 downto 0);
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signal cg_phase : std_logic;
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signal cg_tick : std_logic;
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-- shift register
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signal sreg : std_logic_vector(31 downto 0);
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signal remain : unsigned(5 downto 0);
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signal nxtsyn : std_logic;
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-- input latch
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signal lreg : std_logic_vector(31 downto 0);
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signal filled : std_logic;
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-- helper function
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function to_signed(x : unsigned) return signed is
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begin
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return signed((not x(x'left)) & x(x'left-1 downto 0));
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end to_signed;
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function pack(i,q : unsigned) return slv32_t is
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variable res : slv32_t := (others=>'0');
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begin
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res(31 downto 32-i'length) := std_logic_vector(to_signed(i));
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res(15 downto 16-q'length) := std_logic_vector(to_signed(q));
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return res;
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end pack;
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function pack(i,q : signed) return slv32_t is
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variable res : slv32_t := (others=>'0');
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begin
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res(31 downto 32-i'length) := std_logic_vector(i);
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res(15 downto 16-q'length) := std_logic_vector(q);
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return res;
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end pack;
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-- debug
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signal counter1 : unsigned(15 downto 0);
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signal counter2 : unsigned(15 downto 0);
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begin
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-- clock generator
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process(clk)
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begin
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if rising_edge(clk) then
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-- set default values
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cg_tick <= '0';
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-- update clock-divider
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if cg_div=0 then
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-- toggle phase
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cg_phase <= not cg_phase;
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cg_div <= config.clkdiv;
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-- set 'tick'-flag when generating falling edge
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if cg_phase='1' then
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cg_tick <= '1';
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end if;
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else
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-- stay in current phase
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cg_div <= cg_div-1;
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end if;
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-- update output
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ssc_clk <= cg_phase;
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-- handle reset
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if reset='1' then
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cg_div <= (others=>'0');
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cg_phase <= '0';
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cg_tick <= '0';
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ssc_clk <= '0';
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end if;
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end if;
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end process;
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-- output shift register
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process(clk)
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begin
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if rising_edge(clk) then
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-- wait for output-clock
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if cg_tick='1' then
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-- update output
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ssc_dat <= sreg(sreg'left);
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ssc_syn <= nxtsyn;
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sreg <= sreg(sreg'left-1 downto 0) & '0';
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nxtsyn <= '0';
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-- consume bit
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if remain > 0 then
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remain <= remain - 1;
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end if;
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-- reload shift-register when possible
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if filled='1' and remain<=1 then
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filled <= '0';
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remain <= to_unsigned(32, remain'length);
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nxtsyn <= '1';
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sreg <= lreg;
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end if;
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end if;
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-- handle incoming samples
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if in_clk='1' then
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if filled='0' then
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-- latch sample
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lreg <= pack(in_i,in_q);
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filled <= '1';
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-- apply test-mode
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if config.tmode='1' then
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lreg <= pack(counter1,counter2);
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counter1 <= counter1 + 1;
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counter2 <= counter2 - 1;
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end if;
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else
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--> overflow
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report "usbrx_ssc: input too fast"
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severity warning;
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end if;
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end if;
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-- handle reset
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if reset='1' then
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sreg <= (others=>'0');
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remain <= (others=>'0');
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nxtsyn <= '0';
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lreg <= (others=>'0');
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filled <= '0';
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ssc_syn <= '0';
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ssc_dat <= '0';
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counter1 <= (others=>'0');
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counter2 <= (others=>'1');
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end if;
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end if;
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end process;
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end rtl;
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