From a1539a62b752bc4f494c2395a5e40ffe04dd4f15 Mon Sep 17 00:00:00 2001
From: Istvan Csomortani <istvan.csomortani@analog.com>
Date: Mon, 15 May 2017 12:36:43 +0300
Subject: [PATCH] avl_dacfifo: Integrate util_delay into dac_xfer_out path

The ad_mem_asym memory read interface has a 3 clock cycle delay, from the
moment of the address change until a valid data arrives on the bus;
because the dac_xfer_out is going to validate the outgoing samples (in conjunction
with the DAC VALID, which is free a running signal), this module will compensate
this delay, to prevent duplicated samples in the beginning of the
transaction.
---
 library/altera/avl_dacfifo/avl_dacfifo.v      | 22 ++++++++++++++++---
 library/altera/avl_dacfifo/avl_dacfifo_hw.tcl |  1 +
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/library/altera/avl_dacfifo/avl_dacfifo.v b/library/altera/avl_dacfifo/avl_dacfifo.v
index c22a9aee4..de2e2c0d1 100644
--- a/library/altera/avl_dacfifo/avl_dacfifo.v
+++ b/library/altera/avl_dacfifo/avl_dacfifo.v
@@ -49,7 +49,7 @@ module avl_dacfifo #(
   input                                 dac_valid,
   output  reg [(DAC_DATA_WIDTH-1):0]    dac_data,
   output  reg                           dac_dunf,
-  output  reg                           dac_xfer_out,
+  output                                dac_xfer_out,
 
   input                                 bypass,
 
@@ -77,6 +77,7 @@ module avl_dacfifo #(
   reg                                   dac_bypass_m1 = 1'b0;
   reg                                   dac_bypass = 1'b0;
   reg                                   dac_xfer_out_m1 = 1'b0;
+  reg                                   dac_xfer_out_int = 1'b0;
   reg                                   dac_xfer_out_bypass = 1'b0;
   reg                                   avl_xfer_wren = 1'b0;
   reg                                   avl_dma_xfer_req = 1'b0;
@@ -238,7 +239,7 @@ module avl_dacfifo #(
       if (dac_valid) begin
         dac_data <= (dac_bypass) ? dac_data_bypass_s : dac_data_fifo_s;
       end
-      dac_xfer_out <= (dac_bypass) ? dac_xfer_out_bypass : dac_xfer_fifo_out_s;
+      dac_xfer_out_int <= (dac_bypass) ? dac_xfer_out_bypass : dac_xfer_fifo_out_s;
       dac_dunf <= (dac_bypass) ? dac_dunf_bypass_s : dac_dunf_fifo_s;
     end
 
@@ -251,13 +252,28 @@ module avl_dacfifo #(
       if (dac_valid) begin
         dac_data <= dac_data_fifo_s;
       end
-      dac_xfer_out <= dac_xfer_fifo_out_s;
+      dac_xfer_out_int <= dac_xfer_fifo_out_s;
       dac_dunf <= dac_dunf_fifo_s;
     end
 
   end
   endgenerate
 
+  // the ad_mem_asym memory read interface has a 3 clock cycle delay, from the
+  // moment of the address change until a valid data arrives on the bus;
+  // because the dac_xfer_out is going to validate the outgoing samples (in conjunction
+  // with the DAC VALID, which is free a running signal), this module will compensate
+  // this delay, to prevent duplicated samples in the beginning of the
+  // transaction
+
+  util_delay #(
+    .DATA_WIDTH(1),
+    .DELAY_CYCLES(3)
+  ) i_delay (
+    .clk(dac_clk),
+    .reset(dac_reset),
+    .din(dac_xfer_out_int),
+    .dout(dac_xfer_out));
 
 endmodule
 
diff --git a/library/altera/avl_dacfifo/avl_dacfifo_hw.tcl b/library/altera/avl_dacfifo/avl_dacfifo_hw.tcl
index 653568a3c..257bd4dee 100644
--- a/library/altera/avl_dacfifo/avl_dacfifo_hw.tcl
+++ b/library/altera/avl_dacfifo/avl_dacfifo_hw.tcl
@@ -7,6 +7,7 @@ ad_ip_create avl_dacfifo {Avalon DDR DAC Fifo}
 ad_ip_files avl_dacfifo [list\
   $ad_hdl_dir/library/altera/common/ad_mem_asym.v \
   $ad_hdl_dir/library/common/util_dacfifo_bypass.v \
+  $ad_hdl_dir/library/common/util_delay.v \
   avl_dacfifo_wr.v \
   avl_dacfifo_rd.v \
   avl_dacfifo.v \