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authorPrivate Island Networks <opensource@privateisland.tech>2025-09-01 12:34:17 -0400
committerPrivate Island Networks <opensource@privateisland.tech>2025-09-01 12:34:17 -0400
commitc8b273c80abe98e53828f46079a187975938a56a (patch)
tree410577af8067ee001ba473dcf0c7bcae46d83de1 /source/drop_fifo.v
parentac2bbbd2f816c223ef4dcfa2f8440d9c0c73bffe (diff)
rename source to src
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-/*
- * drop_fifo.v
- *
- * Copyright 2018, 2019, 2020, 2021 Mind Chasers Inc.
- * Copyright 2023 Private Island Networks Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- *
- * function: FIFO that supports dropping data if not kept
- *
- * For more information, see https://privateisland.tech/dev/pi-doc
- *
- */
-
-module drop_fifo(
- input rstn,
- input clk,
- input passthrough, // don't store / delay data, write through instead
- input enable, // enable the FIFO
- input keep, // this packet won't be dropped, start transferring it (writer must be sure FIFO won't run dry during writes)
-
- // input data
- input we_in,
- input [8:0] d_in,
- input wr_done, // keep should occur before wr_done is asserted.
- input rx_eop,
-
- // output data
- output reg we_out,
- output reg [8:0] d_out,
-
- // debug
- output reg active
-);
-
-// local parameters and includes
-
-
-// nets and registers
-reg [10:0] wr_ptr0, wr_ptr1; // wr_ptr0 is updated on each write; wr_ptr1 is updated at end of packet
-reg [10:0] rd_ptr;
-wire [8:0] d_out_internal;
-reg read_run, read_run_m1, read_run_m2; // read continues while read_run is set
-reg kept;
-wire fifo_empty;
-
-/*
- * kept: assert for length of write duration after keep asserts (when enable is active)
- */
-always @(posedge clk, negedge rstn)
- if( !rstn )
- kept <= 1'b0;
- else if ( wr_done )
- kept <= 1'b0;
- else if ( keep && enable )
- kept <= 1'b1;
-
-/*
- * wr_ptr0 logic
- */
-always @(posedge clk, negedge rstn)
- if( !rstn )
- wr_ptr0 <= 'd0;
- else if ( we_in )
- wr_ptr0 <= wr_ptr0 + 1'b1;
-
-/*
- * wr_ptr1 logic
- * sync pointers at end of rx packet for next packet
-*/
-always @(posedge clk, negedge rstn)
- if( !rstn )
- wr_ptr1 <= 'd0;
- else if ( wr_done )
- wr_ptr1 <= wr_ptr0 +1; // a write takes place with wr_done
-
-/*
- * read_run logic
- * continues until the FIFO is empty
- */
-always @(posedge clk, negedge rstn)
- if( !rstn )
- read_run <= 1'b0;
- else if (kept && wr_done)
- read_run <= 1'b1;
- else if ( fifo_empty )
- read_run <= 1'b0;
-
-
-always @(posedge clk, negedge rstn)
- if( !rstn )
- read_run_m1 <= 1'b0;
- else
- read_run_m1 <= read_run;
-
-
-always @(posedge clk, negedge rstn)
- if( !rstn )
- read_run_m2 <= 1'b0;
- else
- read_run_m2 <= read_run_m1;
-
-/*
-* rd_ptr logic
-*/
-always @(posedge clk, negedge rstn)
- if( !rstn )
- rd_ptr <= 'd0;
- else if (kept && wr_done)
- rd_ptr <= wr_ptr1; // set rd_ptr to the beginning of where the write started
- else if (read_run && !fifo_empty)
- rd_ptr <= rd_ptr+ 1'b1;
-
-/*
- * we_out logic
- */
-always @(posedge clk, negedge rstn)
- if( !rstn )
- we_out <= 1'b0;
- else if ( read_run_m1 && read_run_m2 )
- we_out <= 1'b1;
- else
- we_out <= 1'b0;
-
-assign fifo_empty = (wr_ptr1 == rd_ptr);
-
-/*
- * d_out register
- *
- */
-always @(posedge clk, negedge rstn)
- if( !rstn )
- d_out <= 'd0;
- else
- d_out <= d_out_internal;
-
-
-always @(posedge clk, negedge rstn)
- if( !rstn )
- active <= 1'b0;
- else if ( we_in || we_out )
- active <= 1'b1;
- else
- active <= 1'b0;
-
-dpram dpram_fifo(
-.rstn( rstn ),
-.a_clk( clk ),
-.a_clk_e( 1'b1 ),
-.a_we( we_in ),
-.a_oe( 1'b0 ),
-.a_addr( wr_ptr0 ),
-.a_din( d_in ),
-.a_dout( ),
-// port B
-.b_clk( clk ),
-.b_clk_e( read_run ),
-.b_we( 1'b0 ),
-.b_oe( 1'b1 ),
-.b_addr( rd_ptr ),
-.b_din( 9'h0 ),
-.b_dout( d_out_internal )
-);
-
-
-endmodule

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