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-- spwrecvfront implementations. It also implements a receive FIFO and
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-- spwrecvfront implementations. It also implements a receive FIFO and
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-- a transmit FIFO.
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-- a transmit FIFO.
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--
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--
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-- The SpaceWire standard requires that each transceiver use an initial
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-- The SpaceWire standard requires that each transceiver use an initial
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-- signalling rate of 10 Mbit/s. This implies that the system clock frequency
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-- signalling rate of 10 Mbit/s. This implies that the system clock frequency
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-- must be a multiple of 10 MHz. See the datasheet for further details on
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-- must be a multiple of 10 MHz. See the manual for further details on
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-- bitrates and clocking.
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-- bitrates and clocking.
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--
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--
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library ieee;
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library ieee;
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use ieee.std_logic_1164.all;
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use ieee.std_logic_1164.all;
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generic (
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generic (
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-- System clock frequency in Hz.
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-- System clock frequency in Hz.
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-- This must be set to the frequency of "clk". It is used to setup
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-- This must be set to the frequency of "clk". It is used to setup
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-- counters for reset timing, disconnect timeout and to transmit
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-- counters for reset timing, disconnect timeout and to transmit
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-- at 10 Mbit/s during the handshake.
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-- at 10 Mbit/s during the link handshake.
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sysfreq: real;
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sysfreq: real;
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-- Transmit clock frequency in Hz (only if tximpl = impl_fast).
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-- This must be set to the frequency of "txclk". It is used to
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-- transmit at 10 Mbit/s during the link handshake.
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txclkfreq: real := 0.0;
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-- Selection of a receiver front-end implementation.
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-- Selection of a receiver front-end implementation.
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rximpl: spw_implementation_type := impl_generic;
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rximpl: spw_implementation_type := impl_generic;
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-- Maximum number of bits received per system clock
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-- Maximum number of bits received per system clock
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-- (must be 1 in case of impl_generic).
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-- (must be 1 in case of impl_generic).
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-- Enables link start once the Ready state is reached.
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-- Enables link start once the Ready state is reached.
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-- Without autostart or linkstart, the link remains in state Ready.
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-- Without autostart or linkstart, the link remains in state Ready.
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linkstart: in std_logic;
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linkstart: in std_logic;
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-- Do not start link (overrides linkstart and autostart) and/or disconnect
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-- Do not start link (overrides linkstart and autostart) and/or
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-- if the link is in state Run.
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-- disconnect a running link.
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linkdis: in std_logic;
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linkdis: in std_logic;
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-- Scaling factor minus 1, used to scale the system clock into the transmission
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-- Scaling factor minus 1, used to scale the transmit base clock into
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-- signalling rate. The system clock is divided by (unsigned(divcnt) + 1).
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-- the transmission bit rate. The system clock (for impl_generic) or
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-- the txclk (for impl_fast) is divided by (unsigned(txdivcnt) + 1).
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-- Changing this signal will immediately change the transmission rate.
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-- Changing this signal will immediately change the transmission rate.
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-- During link setup, the transmission rate is always 10 Mbit/s.
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-- During link setup, the transmission rate is always 10 Mbit/s.
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txdivcnt: in std_logic_vector(7 downto 0);
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txdivcnt: in std_logic_vector(7 downto 0);
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-- High for one clock cycle to request transmission of a TimeCode.
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-- High for one clock cycle to request transmission of a TimeCode.
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-- Disconnect time (850 ns) in system clocks
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-- Disconnect time (850 ns) in system clocks
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constant disconnect_time: integer := integer(sysfreq * 850.0e-9);
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constant disconnect_time: integer := integer(sysfreq * 850.0e-9);
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-- Initial tx clock scaler (10 Mbit).
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-- Initial tx clock scaler (10 Mbit).
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type impl_to_real_type is array(spw_implementation_type) of real;
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constant tximpl_to_txclk_freq: impl_to_real_type :=
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(impl_generic => sysfreq, impl_fast => txclkfreq);
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constant effective_txclk_freq: real := tximpl_to_txclk_freq(tximpl);
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constant default_divcnt: std_logic_vector(7 downto 0) :=
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constant default_divcnt: std_logic_vector(7 downto 0) :=
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std_logic_vector(to_unsigned(integer(sysfreq / 10.0e6 - 1.0), 8));
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std_logic_vector(to_unsigned(integer(effective_txclk_freq / 10.0e6 - 1.0), 8));
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-- Registers.
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-- Registers.
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type regs_type is record
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type regs_type is record
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-- packet state
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-- packet state
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rxpacket: std_logic; -- '1' when receiving a packet
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rxpacket: std_logic; -- '1' when receiving a packet
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