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