// original source:
// https://github.com/nachiket/tdfc/blob/master/verilog/queues/Q_srl_oreg3_prefull_SIMPLE.v
// Copyright (c) 1999 The Regents of the University of California
// Copyright (c) 2010 The Regents of the University of Pennsylvania
// Copyright (c) 2011 Department of Electrical and Electronic Engineering, Imperial College London
// Copyright (c) 2020 Xilinx
//
// Permission to use, copy, modify, and distribute this software and
// its documentation for any purpose, without fee, and without a
// written agreement is hereby granted, provided that the above copyright
// notice and this paragraph and the following two paragraphs appear in
// all copies.
//
// IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR
// DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
// LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION,
// EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
//
// THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
// INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON
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// PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
//
// Q_srl_oreg3_prefull_SIMPLE.v
//
// - In-page queue with parameterizable depth, bit width
// - Stream I/O is triple (data, valid, back-pressure),
// with EOS concatenated into the data
// - Flow control for input & output is combinationally decoupled
// - 2 <= depth <= 256
// * (depth >= 2) is required to decouple I/O flow control,
// where empty => no produce, full => no consume,
// and depth 1 would ping-pong between the two at half rate
// * (depth <= 256) can be modified
// by changing ''synthesis loop_limit X'' below
// and changing ''addrwidth'' or its log computation
// - 1 <= width
// - Queue storage is in SRL16E, up to depth 16 per LUT per bit-slice,
// plus output register (for fast output)
// - Queue addressing is done by ''addr'' up-down counter
// - Queue fullness is checked by comparator (addr==depth)
// - Queue fullness is pre-computed for next cycle
// - Queue input back-pressure is pre-computed for next cycle
// - Queue output valid (state!=state__empty) is pre-computed for next cycle
// (necessary since SRL data output reg requires non-boolean state)
// - FSM has 3 states (empty, one, more)
// - When empty, continue to emit most recently emitted value (for debugging)
//
// - Queue slots used = / (state==state_empty) ? 0
// | (state==state_one) ? 1
// \ (state==state_more) ? addr+2
// - Queue slots used <= depth
// - Queue slots remaining = depth - used
// = / (state==state_empty) ? depth
// | (state==state_one) ? depth-1
// \ (state==state_more) ? depth-2-addr
//
// - Synplify 7.1 / 8.0
// - Eylon Caspi, 9/11/03, 8/18/04, 3/29/05
`ifdef Q_srl
`else
`define Q_srl
module Q_srl (clock, reset, i_d, i_v, i_b, o_d, o_v, o_b, count);
parameter depth = 16; // - greatest #items in queue (2 <= depth <= 256)
parameter width = 16; // - width of data (i_d, o_d)
`define LOG2 ( (((depth)) ==0) ? 0 /* - depth==0 LOG2=0 */ \
: (((depth-1)>>0)==0) ? 0 /* - depth<=1 LOG2=0 */ \
: (((depth-1)>>1)==0) ? 1 /* - depth<=2 LOG2=1 */ \
: (((depth-1)>>2)==0) ? 2 /* - depth<=4 LOG2=2 */ \
: (((depth-1)>>3)==0) ? 3 /* - depth<=8 LOG2=3 */ \
: (((depth-1)>>4)==0) ? 4 /* - depth<=16 LOG2=4 */ \
: (((depth-1)>>5)==0) ? 5 /* - depth<=32 LOG2=5 */ \
: (((depth-1)>>6)==0) ? 6 /* - depth<=64 LOG2=6 */ \
: (((depth-1)>>7)==0) ? 7 /* - depth<=128 LOG2=7 */ \
: 8) /* - depth<=256 LOG2=8 */
// parameter addrwidth = LOG2; // - width of queue addr
parameter addrwidth =
( (((depth)) ==0) ? 0 // - depth==0 LOG2=0
: (((depth-1)>>0)==0) ? 0 // - depth<=1 LOG2=0
: (((depth-1)>>1)==0) ? 1 // - depth<=2 LOG2=1
: (((depth-1)>>2)==0) ? 2 // - depth<=4 LOG2=2
: (((depth-1)>>3)==0) ? 3 // - depth<=8 LOG2=3
: (((depth-1)>>4)==0) ? 4 // - depth<=16 LOG2=4
: (((depth-1)>>5)==0) ? 5 // - depth<=32 LOG2=5
: (((depth-1)>>6)==0) ? 6 // - depth<=64 LOG2=6
: (((depth-1)>>7)==0) ? 7 // - depth<=128 LOG2=7
: 8) // - depth<=256 LOG2=8
;
input clock;
input reset;
input [width-1:0] i_d; // - input stream data (concat data + eos)
input i_v; // - input stream valid
output i_b; // - input stream back-pressure
output [width-1:0] o_d; // - output stream data (concat data + eos)
output o_v; // - output stream valid
input o_b; // - output stream back-pressure
output [addrwidth:0] count; // - output number of elems in queue
reg [addrwidth-1:0] addr, addr_, a_; // - SRL16 address
// for data output
reg shift_en_; // - SRL16 shift enable
reg [width-1:0] srl [depth-2:0]; // - SRL16 memory
reg shift_en_o_; // - SRLO shift enable
reg [width-1:0] srlo_, srlo // - SRLO output reg
/* synthesis syn_allow_retiming=0 */ ;
parameter state_empty = 2'd0; // - state empty : o_v=0 o_d=UNDEFINED
parameter state_one = 2'd1; // - state one : o_v=1 o_d=srlo
parameter state_more = 2'd2; // - state more : o_v=1 o_d=srlo
// #items in srl = addr+2
reg [1:0] state, state_; // - state register
wire addr_full_; // - true iff addr==depth-2 on NEXT cycle
reg addr_full; // - true iff addr==depth-2
wire addr_zero_; // - true iff addr==0
wire o_v_reg_; // - true iff state_empty on NEXT cycle
reg o_v_reg // - true iff state_empty
/* synthesis syn_allow_retiming=0 */ ;
wire i_b_reg_; // - true iff !full on NEXT cycle
reg i_b_reg // - true iff !full
/* synthesis syn_allow_retiming=0 */ ;
assign addr_full_ = (state_==state_more) && (addr_==depth-2);
// - queue full
assign addr_zero_ = (addr==0); // - queue contains 2 (or 1,0)
assign o_v_reg_ = (state_!=state_empty); // - output valid if non-empty
assign i_b_reg_ = addr_full_; // - input bp if full
assign o_d = srlo; // - output data from queue
assign o_v = o_v_reg; // - output valid if non-empty
assign i_b = i_b_reg; // - input bp if full
assign count = (state==state_more ? addr+2 : (state==state_one ? 1 : 0));
// - ''always'' block with both FFs and SRL16 does not work,
// since FFs need reset but SRL16 does not
always @(posedge clock) begin // - seq always: FFs
if (reset) begin
state <= state_empty;
addr <= 0;
addr_full <= 0;
o_v_reg <= 0;
i_b_reg <= 1;
end
else begin
state <= state_;
addr <= addr_;
addr_full <= addr_full_;
o_v_reg <= o_v_reg_;
i_b_reg <= i_b_reg_;
end
end // always @ (posedge clock)
always @(posedge clock) begin // - seq always: srlo
// - infer enabled output reg at end of shift chain
// - input first element from i_d, all subsequent elements from SRL16
if (reset) begin
srlo <= 0;
end
else begin
if (shift_en_o_) begin
srlo <= srlo_;
end
end
end // always @ (posedge clock)
always @(posedge clock) begin // - seq always: srl
// - infer enabled SRL16E from shifting srl array
// - no reset capability; srl[] contents undefined on reset
if (shift_en_) begin
// synthesis loop_limit 256
for (a_=depth-2; a_>0; a_=a_-1) begin
srl[a_] <= srl[a_-1];
end
srl[0] <= i_d;
end
end // always @ (posedge clock or negedge reset)
always @* begin // - combi always
srlo_ <= 'bx;
shift_en_o_ <= 1'bx;
shift_en_ <= 1'bx;
addr_ <= 'bx;
state_ <= 2'bx;
case (state)
state_empty: begin // - (empty, will not produce)
if (i_v) begin // - empty & i_v => consume
srlo_ <= i_d;
shift_en_o_ <= 1;
shift_en_ <= 1'bx;
addr_ <= 0;
state_ <= state_one;
end
else begin // - empty & !i_v => idle
srlo_ <= 'bx;
shift_en_o_ <= 0;
shift_en_ <= 1'bx;
addr_ <= 0;
state_ <= state_empty;
end
end
state_one: begin // - (contains one)
if (i_v && o_b) begin // - one & i_v & o_b => consume
srlo_ <= 'bx;
shift_en_o_ <= 0;
shift_en_ <= 1;
addr_ <= 0;
state_ <= state_more;
end
else if (i_v && !o_b) begin // - one & i_v & !o_b => cons+prod
srlo_ <= i_d;
shift_en_o_ <= 1;
shift_en_ <= 1;
addr_ <= 0;
state_ <= state_one;
end
else if (!i_v && o_b) begin // - one & !i_v & o_b => idle
srlo_ <= 'bx;
shift_en_o_ <= 0;
shift_en_ <= 1'bx;
addr_ <= 0;
state_ <= state_one;
end
else if (!i_v && !o_b) begin // - one & !i_v & !o_b => produce
srlo_ <= 'bx;
shift_en_o_ <= 0;
shift_en_ <= 1'bx;
addr_ <= 0;
state_ <= state_empty;
end
end // case: state_one
state_more: begin // - (contains more than one)
if (addr_full || (depth==2)) begin
// - (full, will not consume)
// - (full here if depth==2)
if (o_b) begin // - full & o_b => idle
srlo_ <= 'bx;
shift_en_o_ <= 0;
shift_en_ <= 0;
addr_ <= addr;
state_ <= state_more;
end
else begin // - full & !o_b => produce
srlo_ <= srl[addr];
shift_en_o_ <= 1;
shift_en_ <= 0;
// addr_ <= addr-1;
// state_ <= state_more;
addr_ <= addr_zero_ ? 0 : addr-1;
state_ <= addr_zero_ ? state_one : state_more;
end
end
else begin // - (mid: neither empty nor full)
if (i_v && o_b) begin // - mid & i_v & o_b => consume
srlo_ <= 'bx;
shift_en_o_ <= 0;
shift_en_ <= 1;
addr_ <= addr+1;
state_ <= state_more;
end
else if (i_v && !o_b) begin // - mid & i_v & !o_b => cons+prod
srlo_ <= srl[addr];
shift_en_o_ <= 1;
shift_en_ <= 1;
addr_ <= addr;
state_ <= state_more;
end
else if (!i_v && o_b) begin // - mid & !i_v & o_b => idle
srlo_ <= 'bx;
shift_en_o_ <= 0;
shift_en_ <= 0;
addr_ <= addr;
state_ <= state_more;
end
else if (!i_v && !o_b) begin // - mid & !i_v & !o_b => produce
srlo_ <= srl[addr];
shift_en_o_ <= 1;
shift_en_ <= 0;
addr_ <= addr_zero_ ? 0 : addr-1;
state_ <= addr_zero_ ? state_one : state_more;
end
end // else: !if(addr_full)
end // case: state_more
default: begin
srlo_ <= 'bx;
shift_en_o_ <= 1'bx;
shift_en_ <= 1'bx;
addr_ <= 'bx;
state_ <= 2'bx;
end // case: default
endcase // case(state)
end // always @ *
endmodule // Q_srl
`endif // `ifdef Q_srl