Initial revision of FMC arbiter for Novena's on-board FPGA.HEADmaster

4 files changed, 663 insertions, 0 deletions

diff --git a/src/verilog/stm32_fmc/cdc_bus_pulse.v b/src/verilog/stm32_fmc/cdc_bus_pulse.v
new file mode 100644
index 0000000..cc2d8db
--- /dev/null
+++ b/src/verilog/stm32_fmc/cdc_bus_pulse.v
@@ -0,0 +1,145 @@
+//======================================================================
+//
+// cdc_bus_pulse.v
+// ---------------
+// Clock Domain Crossing handler for the Cryptech Novena
+// FPGA framework design.
+//
+// This module is based on design suggested on page 27 of the
+// paper 'Clock Domain Crossing (CDC) Design & Verification Techniques
+// Using SystemVerilog' by Clifford E. Cummings (Sunburst Design, Inc.)
+//
+//
+// Author: Pavel Shatov
+// Copyright (c) 2015, NORDUnet A/S All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions
+// are met:
+// - Redistributions of source code must retain the above copyright
+//   notice, this list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright
+//   notice, this list of conditions and the following disclaimer in the
+//   documentation and/or other materials provided with the distribution.
+//
+// - Neither the name of the NORDUnet nor the names of its contributors may
+//   be used to endorse or promote products derived from this software
+//   without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// HOLDER 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.
+//
+//======================================================================
+
+module cdc_bus_pulse
+  #(parameter   DATA_WIDTH      = 32)     // width of data bus
+   (
+    input wire                   src_clk, // source domain clock
+    input wire [DATA_WIDTH-1:0]  src_din, // data from source clock domain
+    input wire                   src_req, // start transfer pulse from source clock domain
+
+    input wire                   dst_clk, // destination domain clock
+    output wire [DATA_WIDTH-1:0] dst_dout, // data to destination clock domain
+    output wire                  dst_pulse // transfer done pulse to destination clock domain
+    );
+
+   //
+   // Source Side Registers
+   //
+   reg                           src_ff         = 1'b0;                 // transfer request flag
+   reg [DATA_WIDTH-1:0]          src_latch      = {DATA_WIDTH{1'bX}};   // source data buffer
+
+
+   //
+   // Source Request Handler
+   //
+   always @(posedge src_clk)
+     //
+     if (src_req) begin                         // transfer request pulse?
+        src_ff          <= ~src_ff;             // toggle transfer request flag...
+        src_latch       <= src_din;             // ... and capture data in source buffer
+     end
+
+
+   //
+   // Source -> Destination Flag Sync Logic
+   //
+
+   /* ISE may decide to infer SRL here, so we explicitly instantiate slice registers. */
+
+   wire flag_sync_first;        // first FF output
+   wire flag_sync_second;       // second FF output
+   wire flag_sync_third;        // third FF output
+   wire flag_sync_pulse;        // flag toggle detector output
+
+   FDCE ff_sync_first
+     (
+      .C(dst_clk),
+      .D(src_ff),               // capture flag from another clock domain
+      .Q(flag_sync_first),      // metastability can occur here
+      .CLR(1'b0),
+      .CE(1'b1)
+      );
+   FDCE ff_sync_second
+     (
+      .C(dst_clk),
+      .D(flag_sync_first),      // synchronize captured flag to remove metastability
+      .Q(flag_sync_second),     // and pass it to another flip-flop
+      .CLR(1'b0),
+      .CE(1'b1)
+      );
+   FDCE ff_sync_third
+     (
+      .C(dst_clk),
+      .D(flag_sync_second),     // delay synchronized flag in another flip-flip, because we need
+      .Q(flag_sync_third),      // two synchronized flag values (current and delayed) to detect its change
+      .CLR(1'b0),
+      .CE(1'b1)
+      );
+
+   // when delayed flag value differs from its current value, it was changed
+   // by the source side, so there must have been a transfer request
+   assign flag_sync_pulse = flag_sync_second ^ flag_sync_third;
+
+
+   //
+   // Destination Side Registers
+   //
+   reg  dst_pulse_reg   = 1'b0;                         // transfer done flag
+   reg [DATA_WIDTH-1:0] dst_latch = {DATA_WIDTH{1'bX}}; // destination data buffer
+
+   assign dst_pulse     = dst_pulse_reg;
+   assign dst_dout      = dst_latch;
+
+   //
+   // Destination Request Handler
+   //
+   always @(posedge dst_clk) begin
+      //
+      dst_pulse_reg <= flag_sync_pulse; // generate pulse if flag change was detected
+      //
+      if (flag_sync_pulse)
+        dst_latch <= src_latch;
+      /* By the time destination side receives synchronized flag
+       * value, data should be stable, we can safely capture and store
+       * it in the destination buffer.
+       */
+
+   end
+
+
+endmodule
+
+//======================================================================
+// EOF cdc_bus_pulse.v
+//======================================================================
diff --git a/src/verilog/stm32_fmc/fmc_arbiter.v b/src/verilog/stm32_fmc/fmc_arbiter.v
new file mode 100644
index 0000000..b9be05c
--- /dev/null
+++ b/src/verilog/stm32_fmc/fmc_arbiter.v
@@ -0,0 +1,295 @@
+//======================================================================
+//
+// fmc_arbiter.v
+// -------------
+// Port arbiter for the FMC interface for the Cryptech
+// Novena FPGA + STM32 Bridge Board framework.
+//
+//
+// Author: Pavel Shatov
+// Copyright (c) 2015, NORDUnet A/S All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions
+// are met:
+// - Redistributions of source code must retain the above copyright
+//   notice, this list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright
+//   notice, this list of conditions and the following disclaimer in the
+//   documentation and/or other materials provided with the distribution.
+//
+// - Neither the name of the NORDUnet nor the names of its contributors may
+//   be used to endorse or promote products derived from this software
+//   without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// HOLDER 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.
+//
+//======================================================================
+
+module fmc_arbiter
+  (
+		// fmc bus

+		fmc_clk,

+		fmc_a, fmc_d,
+		fmc_ne1, fmc_nl, fmc_nwe, fmc_noe, fmc_nwait,
+		
+		// system clock
+		sys_clk,
+
+		// user bus
+		sys_addr, 
+		sys_wr_en,
+		sys_data_out,
+		sys_rd_en,
+		sys_data_in
+   );

+	

+	

+	//

+	// Parameters

+	//

+	parameter NUM_ADDR_BITS = 22;

+	

+	

+	//

+	// Ports

+	//
+	input		wire								fmc_clk;

+	input		wire	[NUM_ADDR_BITS-1:0]	fmc_a;

+	inout		wire	[             31:0]	fmc_d;
+	input		wire								fmc_ne1;

+	input		wire								fmc_nl;

+	input		wire								fmc_nwe;

+	input		wire								fmc_noe;

+	output	wire								fmc_nwait;

+	

+	input		wire								sys_clk;

+	

+	output	wire	[NUM_ADDR_BITS-1:0]	sys_addr;
+	output	wire								sys_wr_en;
+	output	wire	[             31:0]	sys_data_out;
+	output	wire								sys_rd_en;
+	input		wire	[             31:0]	sys_data_in;
+		
+
+   //
+   // Data Bus PHY
+   //
+
+   /* PHY is needed to control bi-directional data bus. */
+
+   wire	[31: 0]  d_ro;   // value read from pins (receiver output)
+   reg	[31: 0]	d_di;   // value drives onto pins (driver input)
+
+   fmc_d_phy #

+	(

+		.BUS_WIDTH(32)

+	)

+	d_phy
+	(
+		.buf_io(fmc_d),          // <-- connect directly to top-level bi-dir port
+		.buf_di(d_di),
+		.buf_ro(d_ro),
+		.buf_t(fmc_noe)          // <-- bus direction is controlled by STM32
+	);

+	
+
+   //
+   // FSM
+   //
+   localparam   FMC_FSM_STATE_INIT      			= 5'b0_0_000; // arbiter is idle
+
+   localparam   FMC_FSM_STATE_WRITE_START 		= 5'b1_1_000; // got address to write at
+   localparam   FMC_FSM_STATE_WRITE_LATENCY_1	= 5'b1_1_001; // dummy state to compensate STM32's latency

+	localparam   FMC_FSM_STATE_WRITE_LATENCY_2	= 5'b1_1_010; // dummy state to compensate STM32's latency

+	localparam   FMC_FSM_STATE_WRITE_LATENCY_3	= 5'b1_1_011; // dummy state to compensate STM32's latency

+	localparam   FMC_FSM_STATE_WRITE_DATABEAT		= 5'b1_1_100; // got data to write
+   localparam   FMC_FSM_STATE_WRITE_WAIT			= 5'b1_1_101; // request to user-side logic sent
+   localparam   FMC_FSM_STATE_WRITE_DONE			= 5'b1_1_111; // user-side logic acknowledged transaction
+
+   localparam   FMC_FSM_STATE_READ_START  		= 5'b1_0_000; // got address to read from

+	localparam   FMC_FSM_STATE_READ_LATENCY_1		= 5'b1_0_001; // dummy state to compensate STM32's latency

+	localparam   FMC_FSM_STATE_READ_LATENCY_2		= 5'b1_0_010; // dummy state to compensate STM32's latency

+	localparam   FMC_FSM_STATE_READ_LATENCY_3		= 5'b1_0_011; // dummy state to compensate STM32's latency
+   localparam   FMC_FSM_STATE_READ_WAIT   		= 5'b1_0_101; // request to user-side logic sent
+   localparam   FMC_FSM_STATE_READ_READY  		= 5'b1_0_110; // got acknowledge from user logic
+   localparam   FMC_FSM_STATE_READ_DATABEAT		= 5'b1_0_100; // returned data to master
+   localparam   FMC_FSM_STATE_READ_DONE   		= 5'b1_0_111; // transaction complete
+
+   reg [              4:0]  fmc_fsm_state   = FMC_FSM_STATE_INIT;   		// fsm state
+   reg [NUM_ADDR_BITS-1:0]  fmc_addr_latch  = {NUM_ADDR_BITS{1'bX}};		// transaction address

+	reg [             31:0]  fmc_data_latch = {32{1'bX}};						// write data latch
+
+   /* These flags are used to wake up from INIT state. */
+   wire         fmc_write_start_flag = (fmc_ne1 == 1'b0) && (fmc_nwe == 1'b0) && (fmc_nl == 1'b0);
+   wire         fmc_read_start_flag  = (fmc_ne1 == 1'b0) && (fmc_nwe == 1'b1) && (fmc_nl == 1'b0);
+
+   /* These are transaction response flag and data from user-side logic. */
+   wire         fmc_user_ack;
+   wire [31: 0] fmc_user_data;
+
+   //
+   // FSM Transition Logic
+   //
+   always @(posedge fmc_clk)
+		//
+		case (fmc_fsm_state)
+			//
+			// INIT -> WRITE, INIT -> READ
+			//
+			FMC_FSM_STATE_INIT: begin

+				//
+				if (fmc_write_start_flag)	fmc_fsm_state	<= FMC_FSM_STATE_WRITE_START;
+				if (fmc_read_start_flag)	fmc_fsm_state	<= FMC_FSM_STATE_READ_START;

+				//
+			end
+			//
+			// WRITE
+			//
+			FMC_FSM_STATE_WRITE_START:										fmc_fsm_state  <= FMC_FSM_STATE_WRITE_LATENCY_1;
+			FMC_FSM_STATE_WRITE_LATENCY_1:								fmc_fsm_state	<= FMC_FSM_STATE_WRITE_LATENCY_2;

+			FMC_FSM_STATE_WRITE_LATENCY_2:								fmc_fsm_state	<= FMC_FSM_STATE_WRITE_LATENCY_3;

+			FMC_FSM_STATE_WRITE_LATENCY_3:								fmc_fsm_state	<= FMC_FSM_STATE_WRITE_DATABEAT;

+			FMC_FSM_STATE_WRITE_DATABEAT:									fmc_fsm_state  <= FMC_FSM_STATE_WRITE_WAIT;
+			FMC_FSM_STATE_WRITE_WAIT:			if (fmc_user_ack)		fmc_fsm_state	<= FMC_FSM_STATE_WRITE_DONE;
+			FMC_FSM_STATE_WRITE_DONE:										fmc_fsm_state  <= FMC_FSM_STATE_INIT;
+			//
+			// READ
+			//
+			FMC_FSM_STATE_READ_START:									fmc_fsm_state	<= FMC_FSM_STATE_READ_LATENCY_1;

+			FMC_FSM_STATE_READ_LATENCY_1:								fmc_fsm_state	<= FMC_FSM_STATE_READ_LATENCY_2;

+			FMC_FSM_STATE_READ_LATENCY_2:								fmc_fsm_state	<= FMC_FSM_STATE_READ_LATENCY_3;

+			FMC_FSM_STATE_READ_LATENCY_3:								fmc_fsm_state	<= FMC_FSM_STATE_READ_WAIT;
+			FMC_FSM_STATE_READ_WAIT:			if (fmc_user_ack)	fmc_fsm_state	<= FMC_FSM_STATE_READ_READY;
+			FMC_FSM_STATE_READ_READY:									fmc_fsm_state	<= FMC_FSM_STATE_READ_DATABEAT;
+			FMC_FSM_STATE_READ_DATABEAT:								fmc_fsm_state	<= FMC_FSM_STATE_READ_DONE;
+			FMC_FSM_STATE_READ_DONE:									fmc_fsm_state	<= FMC_FSM_STATE_INIT;
+			//

+			default:															fmc_fsm_state	<= FMC_FSM_STATE_INIT;
+			//
+		endcase
+
+
+   //
+   // Address Latch
+   //
+   always @(posedge fmc_clk)
+     //
+     if ((fmc_fsm_state == FMC_FSM_STATE_INIT) && (fmc_write_start_flag || fmc_read_start_flag))

+		//
+		fmc_addr_latch <= fmc_a;
+

+

+	//
+   // Additional Write Logic (Data Latch)
+   //
+   always @(posedge fmc_clk)
+     //
+     if (fmc_fsm_state == FMC_FSM_STATE_WRITE_LATENCY_3)

+		//
+       fmc_data_latch <= d_ro;

+
+
+   //
+   // Additional Read Logic (Read Latch)
+   //

+	

+	/* Note that this register is updated on the falling edge of FMC_CLK, because

+	 * STM32 samples bi-directional data bus on the rising edge.

+	 */

+	
+   always @(negedge fmc_clk)
+     //
+     if (fmc_fsm_state == FMC_FSM_STATE_READ_DATABEAT)

+		//

+		d_di <= fmc_user_data;

+	
+        
+
+   //
+   // Wait Logic
+   //
+   reg  fmc_wait_reg    = 1'b0;
+
+   always @(posedge fmc_clk)
+     //

+	  begin
+        //
+        if ( (fmc_fsm_state == FMC_FSM_STATE_WRITE_START) ||

+				 (fmc_fsm_state == FMC_FSM_STATE_READ_START) )
+          fmc_wait_reg  <= 1'b1;                // start waiting for read/write to complete
+        /*
+        if ( (fmc_fsm_state == FMC_FSM_STATE_WRITE_DONE) ||
+             (fmc_fsm_state == FMC_FSM_STATE_READ_READY) )
+          fmc_wait_reg  <= 1'b0;
+        */
+        if (fmc_fsm_state == FMC_FSM_STATE_INIT)
+          fmc_wait_reg  <= 1'b0;                // fsm is idle, no need to wait any more
+        //
+     end
+
+   assign fmc_nwait = ~fmc_wait_reg;
+
+
+   /* These flags are used to generate 1-cycle pulses to trigger CDC
+    * transaction.  Note that FSM goes from WRITE_DATABEAT to WRITE_WAIT and from
+    * READ_LATENCY_3 to READ_WAIT unconditionally, so these flags will always be
+    * active for 1 cycle only, which is exactly what we need.
+    */
+
+   wire arbiter_write_req_pulse = (fmc_fsm_state == FMC_FSM_STATE_WRITE_DATABEAT)  ? 1'b1 : 1'b0;
+   wire arbiter_read_req_pulse  = (fmc_fsm_state == FMC_FSM_STATE_READ_LATENCY_3)  ? 1'b1 : 1'b0;
+
+   //
+   // CDC Block
+   //
+
+   /* This block is used to transfer request data from FMC_CLK clock domain to
+    * SYS_CLK clock domain and then transfer acknowledge from SYS_CLK to FMC_CLK
+    * clock domain in return. Af first 1+1+22+32 = 56 bits are transfered,
+    * these are: write flag, read flag, address, write data. During read transaction

+	 * some bogus write data is passed, which is not used later anyway.

+	 * During read requests 32 bits of data are returned, during write requests

+	 * 32 bits of bogus data are returned, that are never used later.
+    */
+
+   fmc_arbiter_cdc #

+	(

+		.NUM_ADDR_BITS(NUM_ADDR_BITS)

+	)

+	fmc_cdc
+	(
+      .fmc_clk(fmc_clk),
+
+      .fmc_req(arbiter_write_req_pulse | arbiter_read_req_pulse),
+      .fmc_ack(fmc_user_ack),
+
+      .fmc_din({arbiter_write_req_pulse, arbiter_read_req_pulse, fmc_addr_latch, fmc_data_latch}),
+      .fmc_dout(fmc_user_data),
+
+      .sys_clk(sys_clk),
+      .sys_addr(sys_addr),
+      .sys_wren(sys_wr_en),
+      .sys_data_out(sys_data_out),
+      .sys_rden(sys_rd_en),
+      .sys_data_in(sys_data_in)
+	);
+
+
+endmodule
+

+
+//======================================================================
+// EOF fmc_arbiter.v
+//======================================================================
diff --git a/src/verilog/stm32_fmc/fmc_arbiter_cdc.v b/src/verilog/stm32_fmc/fmc_arbiter_cdc.v
new file mode 100644
index 0000000..4e1437a
--- /dev/null
+++ b/src/verilog/stm32_fmc/fmc_arbiter_cdc.v
@@ -0,0 +1,146 @@
+//======================================================================
+//
+// fmc_arbiter_cdc.v
+// -----------------
+// The actual clock domain crossing handler of the FMC arbiter
+// for the Cryptech Novena FPGA framework.
+//
+//
+// Author: Pavel Shatov
+// Copyright (c) 2015, NORDUnet A/S All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions
+// are met:
+// - Redistributions of source code must retain the above copyright
+//   notice, this list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright
+//   notice, this list of conditions and the following disclaimer in the
+//   documentation and/or other materials provided with the distribution.
+//
+// - Neither the name of the NORDUnet nor the names of its contributors may
+//   be used to endorse or promote products derived from this software
+//   without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// HOLDER 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.
+//
+//======================================================================
+
+module fmc_arbiter_cdc #

+  (

+	parameter NUM_ADDR_BITS = 22

+  )

+  (
+   input wire      	 		   				fmc_clk, // fmc clock
+   input wire       	  		 					fmc_req, // fmc transaction request
+   output wire      	  		 					fmc_ack, // fmc transaction acknowledge
+   input wire [NUM_ADDR_BITS+32+2-1: 0]	fmc_din, // data from cpu to fpga (write access)
+   output wire [31: 0] 							fmc_dout, // data from fpga to cpu (read access)
+
+   input wire          					sys_clk, // user internal clock
+   output wire [NUM_ADDR_BITS-1: 0]	sys_addr, // user access address
+   output wire         					sys_wren, // user write flag
+   output wire [31: 0] 					sys_data_out, // user write data
+   output wire         					sys_rden, // user read flag
+   input wire [31: 0]  					sys_data_in   // user read data
+   );
+
+
+   //
+   // FMC_CLK -> SYS_CLK Request
+   //
+   wire                			sys_req;         // request pulse in sys_clk clock domain
+   wire [NUM_ADDR_BITS+32+2-1: 0]	sys_dout;        // transaction data in sys_clk clock domain
+
+   cdc_bus_pulse #
+     (
+      .DATA_WIDTH(NUM_ADDR_BITS+32+2)   // {write, read, addr, data}
+      )
+   cdc_fmc_sys
+     (
+      .src_clk(fmc_clk),
+      .src_din(fmc_din),
+      .src_req(fmc_req),
+
+      .dst_clk(sys_clk),
+      .dst_dout(sys_dout),
+      .dst_pulse(sys_req)
+      );
+
+
+   //
+   // Output Registers
+   //
+   reg                 			sys_wren_reg     = 1'b0;
+   reg                 			sys_rden_reg     = 1'b0;
+   reg [NUM_ADDR_BITS-1: 0]	sys_addr_reg     = {NUM_ADDR_BITS{1'bX}};
+   reg [31: 0]         			sys_data_out_reg = {32{1'bX}};
+   
+   assign sys_wren      = sys_wren_reg;
+   assign sys_rden      = sys_rden_reg;
+   assign sys_addr      = sys_addr_reg;
+   assign sys_data_out  = sys_data_out_reg;
+   
+
+   //
+   // System (User) Clock Access Handler
+   //
+   always @(posedge sys_clk)
+     //
+     if (sys_req)                               // request detected?
+       begin
+          sys_wren_reg     <= sys_dout[32+NUM_ADDR_BITS+1];     // set write flag if needed
+          sys_rden_reg     <= sys_dout[32+NUM_ADDR_BITS+0];     // set read flag if needed
+          sys_addr_reg     <= sys_dout[32+NUM_ADDR_BITS-1:32];  // set operation address
+          sys_data_out_reg <= sys_dout[31: 0];  // set data to write
+       end
+     else                                       // no request active
+       begin
+          sys_wren_reg  <=  1'b0;               // clear write flag
+          sys_rden_reg  <=  1'b0;               // clear read flag
+       end
+
+
+   //
+   // System Request 2-cycle delay to compensate registered mux delay in user-side logic
+   //
+   reg  [ 1: 0] sys_req_dly     = 2'b00;
+
+   always @(posedge sys_clk)
+     sys_req_dly <= {sys_req_dly[0], sys_req};
+
+
+   //
+   // SYS_CLK -> FMC_CLK Acknowledge
+   //
+   cdc_bus_pulse #
+     (
+      .DATA_WIDTH(32)
+      )
+   cdc_sys_fmc
+     (
+      .src_clk(sys_clk),
+      .src_din(sys_data_in),
+      .src_req(sys_req_dly[1]),
+
+      .dst_clk(fmc_clk),
+      .dst_dout(fmc_dout),
+      .dst_pulse(fmc_ack)
+      );
+
+endmodule
+
+//======================================================================
+// EOF fmc_arbiter_cdc.v
+//======================================================================
diff --git a/src/verilog/stm32_fmc/fmc_d_phy.v b/src/verilog/stm32_fmc/fmc_d_phy.v
new file mode 100644
index 0000000..ce643bb
--- /dev/null
+++ b/src/verilog/stm32_fmc/fmc_d_phy.v
@@ -0,0 +1,77 @@
+//======================================================================
+//
+// fmc_d_phy.v
+// ------------
+// IO buffer module for the FMC D port.
+//
+//
+// Author: Pavel Shatov
+// Copyright (c) 2015, NORDUnet A/S All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions
+// are met:
+// - Redistributions of source code must retain the above copyright
+//   notice, this list of conditions and the following disclaimer.
+//
+// - Redistributions in binary form must reproduce the above copyright
+//   notice, this list of conditions and the following disclaimer in the
+//   documentation and/or other materials provided with the distribution.
+//
+// - Neither the name of the NORDUnet nor the names of its contributors may
+//   be used to endorse or promote products derived from this software
+//   without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// HOLDER 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.
+//
+//======================================================================
+
+module fmc_d_phy
+  #(parameter BUS_WIDTH = 16)
+   (
+    inout wire [BUS_WIDTH-1:0]  buf_io, // connect directly to top-level pins
+    input wire [BUS_WIDTH-1:0]  buf_di, // drive input (value driven onto pins)
+    output wire [BUS_WIDTH-1:0] buf_ro, // receiver output (value read from pins)
+    input wire                  buf_t   // tristate control (driver is disabled during tristate)
+    );
+
+   //
+   // IOBUFs
+   //
+   genvar                       i;
+   generate
+      for (i = 0; i < BUS_WIDTH; i = i+1)
+        begin: fmc_d
+           //
+           IOBUF #
+               (
+                .IOSTANDARD("LVCMOS33"),
+                .DRIVE(8),
+                .SLEW("FAST")
+                )
+           IOBUF_inst
+               (
+                .IO(buf_io[i]),
+                .O(buf_ro[i]),
+                .I(buf_di[i]),
+                .T(buf_t)
+                );
+           //
+        end
+   endgenerate
+
+endmodule
+
+//======================================================================
+// EOF fmc_d_phy.v
+//======================================================================