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+/////////////////////////////////////////////////////////////////////
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+//// ////
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+//// WISHBONE rev.B2 compliant synthesizable I2C Slave model ////
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+//// ////
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+//// ////
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+//// Authors: Richard Herveille (richard@asics.ws) www.asics.ws ////
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+//// John Sheahan (jrsheahan@optushome.com.au) ////
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+//// ////
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+//// Downloaded from: http://www.opencores.org/projects/i2c/ ////
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+//// ////
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+/////////////////////////////////////////////////////////////////////
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+//// ////
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+//// Copyright (C) 2001,2002 Richard Herveille ////
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+//// richard@asics.ws ////
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+//// ////
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+//// This source file may be used and distributed without ////
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+//// restriction provided that this copyright statement is not ////
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+//// removed from the file and that any derivative work contains ////
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+//// the original copyright notice and the associated disclaimer.////
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+//// ////
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+//// THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY ////
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+//// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED ////
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+//// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS ////
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+//// FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL THE AUTHOR ////
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+//// OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, ////
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+//// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES ////
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+//// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE ////
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+//// GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR ////
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+//// BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF ////
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+//// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ////
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+//// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT ////
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+//// OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE ////
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+//// POSSIBILITY OF SUCH DAMAGE. ////
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+//// ////
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+/////////////////////////////////////////////////////////////////////
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+
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+// CVS Log
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+//
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+// $Id: i2c_slave_model.v,v 1.7 2006-09-04 09:08:51 rherveille Exp $
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+//
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+// $Date: 2006-09-04 09:08:51 $
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+// $Revision: 1.7 $
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+// $Author: rherveille $
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+// $Locker: $
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+// $State: Exp $
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+//
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+// Change History:
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+// $Log: not supported by cvs2svn $
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+// Revision 1.6 2005/02/28 11:33:48 rherveille
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+// Fixed Tsu:sta timing check.
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+// Added Thd:sta timing check.
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+//
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+// Revision 1.5 2003/12/05 11:05:19 rherveille
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+// Fixed slave address MSB='1' bug
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+//
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+// Revision 1.4 2003/09/11 08:25:37 rherveille
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+// Fixed a bug in the timing section. Changed 'tst_scl' into 'tst_sto'.
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+//
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+// Revision 1.3 2002/10/30 18:11:06 rherveille
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+// Added timing tests to i2c_model.
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+// Updated testbench.
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+//
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+// Revision 1.2 2002/03/17 10:26:38 rherveille
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+// Fixed some race conditions in the i2c-slave model.
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+// Added debug information.
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+// Added headers.
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+//
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+
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+//`include "timescale.v"
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+`timescale 1ns / 1ns
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+
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+module ExtI2cSlaveEmul (scl, sda);
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+
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+ //
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+ // parameters
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+ //
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+ //parameter I2C_ADR = 7'b001_0000;
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+ parameter I2C_ADR = 7'b100_1000;
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+
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+ //
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+ // input && outpus
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+ //
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+ input scl;
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+ inout sda;
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+
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+ //
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+ // Variable declaration
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+ //
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+ wire debug = 1'b1;
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+
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+ reg [7:0] mem [3:0]; // initiate memory
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+ reg [7:0] mem_adr = 8'h0000; // memory address
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+ reg [7:0] mem_do = 8'h0000; // memory data output
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+
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+ reg sta, d_sta;
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+ reg sto, d_sto;
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+
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+ reg [7:0] sr; // 8bit shift register
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+ reg rw; // read/write direction
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+
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+ wire my_adr; // my address called ??
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+ wire i2c_reset; // i2c-statemachine reset
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+ reg [2:0] bit_cnt; // 3bit downcounter
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+ wire acc_done; // 8bits transfered
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+ reg ld; // load downcounter
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+
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+ reg sda_o; // sda-drive level
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+ wire sda_dly; // delayed version of sda
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+
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+ // statemachine declaration
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+ parameter idle = 3'b000;
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+ parameter slave_ack = 3'b001;
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+ parameter get_mem_adr = 3'b010;
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+ parameter gma_ack = 3'b011;
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+ parameter data = 3'b100;
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+ parameter data_ack = 3'b101;
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+
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+ reg [2:0] state; // synopsys enum_state
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+
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+ //
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+ // module body
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+ //
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+
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+ initial
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+ begin
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+ sda_o = 1'b1;
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+ state = idle;
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+ end
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+
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+ initial begin
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+ mem[0] = 8'hFF;
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+ mem[1] = 8'hE0;
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+ mem[2] = 8'hFF;
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+ mem[3] = 8'hFF;
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+ end
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+
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+ // generate shift register
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+ always @(posedge scl)
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+ sr <= #1 {sr[6:0],sda};
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+
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+ //detect my_address
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+ assign my_adr = (sr[7:1] == I2C_ADR);
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+ // FIXME: This should not be a generic assign, but rather
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+ // qualified on address transfer phase and probably reset by stop
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+
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+ //generate bit-counter
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+ always @(posedge scl)
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+ if(ld)
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+ bit_cnt <= #1 3'b111;
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+ else
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+ bit_cnt <= #1 bit_cnt - 3'h1;
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+
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+ //generate access done signal
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+ assign acc_done = !(|bit_cnt);
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+
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+ // generate delayed version of sda
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+ // this model assumes a hold time for sda after the falling edge of scl.
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+ // According to the Phillips i2c spec, there s/b a 0 ns hold time for sda
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+ // with regards to scl. If the data changes coincident with the clock, the
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+ // acknowledge is missed
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+ // Fix by Michael Sosnoski
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+ assign #1 sda_dly = sda;
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+
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+
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+ //detect start condition
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+ always @(negedge sda)
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+ if(scl)
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+ begin
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+ sta <= #1 1'b1;
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+ d_sta <= #1 1'b0;
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+ sto <= #1 1'b0;
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+
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+ if(debug)
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+ $display("DEBUG i2c_slave; start condition detected at %t", $time);
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+ end
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+ else
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+ sta <= #1 1'b0;
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+
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+ always @(posedge scl)
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+ d_sta <= #1 sta;
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+
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+ // detect stop condition
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+ always @(posedge sda)
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+ if(scl)
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+ begin
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+ sta <= #1 1'b0;
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+ sto <= #1 1'b1;
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+
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+ if(debug)
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+ $display("DEBUG i2c_slave; stop condition detected at %t", $time);
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+ end
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+ else
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+ sto <= #1 1'b0;
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+
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+ //generate i2c_reset signal
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+ assign i2c_reset = sta || sto;
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+
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+ // generate statemachine
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+ always @(negedge scl or posedge sto)
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+ if (sto || (sta && !d_sta) )
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+ begin
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+ state <= #1 idle; // reset statemachine
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+
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+ sda_o <= #1 1'b1;
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+ ld <= #1 1'b1;
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+ end
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+ else
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+ begin
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+ // initial settings
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+ sda_o <= #1 1'b1;
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+ ld <= #1 1'b0;
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+
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+ case(state) // synopsys full_case parallel_case
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+ idle: // idle state
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+ if (acc_done && my_adr)
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+ begin
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+ state <= #1 slave_ack;
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+ rw <= #1 sr[0];
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+ sda_o <= #1 1'b0; // generate i2c_ack
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+
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+ #2;
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+ if(debug && rw)
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+ $display("DEBUG i2c_slave; command byte received (read) at %t", $time);
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+ if(debug && !rw)
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+ $display("DEBUG i2c_slave; command byte received (write) at %t", $time);
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+
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+ if(rw)
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+ begin
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+ mem_do <= #1 mem[mem_adr];
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+
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+ if(debug)
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+ begin
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+ #2 $display("DEBUG i2c_slave; data block read %x from address %x (1)", mem_do, mem_adr);
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+ #2 $display("DEBUG i2c_slave; memcheck [0]=%x, [1]=%x, [2]=%x", mem[4'h0], mem[4'h1], mem[4'h2]);
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+ end
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+ end
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+ end
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+
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+ slave_ack:
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+ begin
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+ if(rw)
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+ begin
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+ state <= #1 data;
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+ sda_o <= #1 mem_do[7];
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+ end
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+ else
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+ state <= #1 get_mem_adr;
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+
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+ ld <= #1 1'b1;
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+ end
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+
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+ get_mem_adr: // wait for memory address
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+ if(acc_done)
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+ begin
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+ state <= #1 gma_ack;
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+ mem_adr <= #1 sr; // store memory address
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+ sda_o <= #1 !(sr <= 15); // generate i2c_ack, for valid address
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+
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+ if(debug)
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+ #1 $display("DEBUG i2c_slave; address received. adr=%x, ack=%b", sr, sda_o);
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+ end
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+
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+ gma_ack:
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+ begin
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+ state <= #1 data;
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+ ld <= #1 1'b1;
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+ end
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+
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+ data: // receive or drive data
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+ begin
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+ if(rw)
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+ sda_o <= #1 mem_do[7];
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+
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+ if(acc_done)
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+ begin
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+ state <= #1 data_ack;
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+ mem_adr <= #2 mem_adr + 8'h1;
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+ sda_o <= #1 (rw && (mem_adr <= 15) ); // send ack on write, receive ack on read
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+
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+ if(rw)
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+ begin
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+ #3 mem_do <= mem[mem_adr];
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+
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+ if(debug)
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+ #5 $display("DEBUG i2c_slave; data block read %x from address %x (2)", mem_do, mem_adr);
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+ end
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+
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+ /*if(!rw)
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+ begin
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+ mem[ mem_adr[3:0] ] <= #1 sr; // store data in memory
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+
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+ if(debug)
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+ #2 $display("DEBUG i2c_slave; data block write %x to address %x", sr, mem_adr);
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+ end*/
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+ end
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+ end
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+
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+ data_ack:
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+ begin
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+ ld <= #1 1'b1;
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+
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+ if(rw)
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+ if(sr[0]) // read operation && master send NACK
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+ begin
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+ state <= #1 idle;
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+ sda_o <= #1 1'b1;
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+ end
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+ else
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+ begin
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+ state <= #1 data;
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+ sda_o <= #1 mem_do[7];
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+ end
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+ else
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+ begin
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+ state <= #1 data;
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+ sda_o <= #1 1'b1;
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+ end
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+ end
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+
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+ endcase
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+ end
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+
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+ // read data from memory
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+ always @(posedge scl)
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+ if(!acc_done && rw)
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+ mem_do <= #1 {mem_do[6:0], 1'b1}; // insert 1'b1 for host ack generation
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+
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+ // generate tri-states
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+ assign sda = sda_o ? 1'bz : 1'b0;
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+
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+
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+ //
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+ // Timing checks
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+ //
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+
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+ wire tst_sto = sto;
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+ wire tst_sta = sta;
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+
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+ specify
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+ specparam normal_scl_low = 4700,
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+ normal_scl_high = 4000,
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+ normal_tsu_sta = 4700,
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+ normal_thd_sta = 4000,
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+ normal_tsu_sto = 4000,
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+ normal_tbuf = 4700,
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+
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+ fast_scl_low = 1300,
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+ fast_scl_high = 600,
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+ fast_tsu_sta = 1300,
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+ fast_thd_sta = 600,
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+ fast_tsu_sto = 600,
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+ fast_tbuf = 1300;
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+
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+ $width(negedge scl, normal_scl_low); // scl low time
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+ $width(posedge scl, normal_scl_high); // scl high time
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+
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+ $setup(posedge scl, negedge sda &&& scl, normal_tsu_sta); // setup start
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+ $setup(negedge sda &&& scl, negedge scl, normal_thd_sta); // hold start
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+ $setup(posedge scl, posedge sda &&& scl, normal_tsu_sto); // setup stop
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+
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+ $setup(posedge tst_sta, posedge tst_sto, normal_tbuf); // stop to start time
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+ endspecify
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+
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+endmodule
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+
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+
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