From a7b8bdc06c20b9b8f741f7e3d88854ee804de995 Mon Sep 17 00:00:00 2001
From: Sebastian Holzapfel <me@sebholzapfel.com>
Date: Fri, 22 Mar 2024 21:16:54 +0100
Subject: [PATCH 1/7] gateware: swap clk_fs for more idiomatic strobe works on
 mirror core

---
 gateware/boards/icebreaker/sysmgr.v | 10 ----------
 gateware/cal/cal.sv                 |  9 ++-------
 gateware/cores/mirror.sv            |  2 +-
 gateware/drivers/ak4619.sv          | 26 ++++++++++----------------
 gateware/eurorack_pmod.sv           |  6 +++---
 gateware/top.sv                     | 17 +++++++++++++----
 6 files changed, 29 insertions(+), 41 deletions(-)

diff --git a/gateware/boards/icebreaker/sysmgr.v b/gateware/boards/icebreaker/sysmgr.v
index 70dd906..41580c0 100644
--- a/gateware/boards/icebreaker/sysmgr.v
+++ b/gateware/boards/icebreaker/sysmgr.v
@@ -8,7 +8,6 @@ module sysmgr (
     // but we leave all this PLL logic here as you might need to scale
     // the clock down to 12m on different boards.
 	output wire clk_256fs,
-	output wire clk_fs,
 	output wire rst_out
 );
 
@@ -22,12 +21,10 @@ module sysmgr (
 	wire rst_i;
 
 	reg [7:0] rst_cnt;
-	reg [7:0] clkdiv;
 
 	assign clk_256fs = clk_1x_i;
 	assign pll_reset_n = ~rst_in;
 	assign rst_i = rst_cnt[7];
-	assign clk_fs = clkdiv[7];
 
 	// PLL instance
 `ifndef COCOTB_SIM
@@ -69,13 +66,6 @@ module sysmgr (
 		else if (rst_cnt[7])
 			rst_cnt <= rst_cnt + 1;
 
-    always @(posedge clk_256fs)
-        if (rst_i)
-            clkdiv <= 8'h00;
-        else
-            clkdiv <= clkdiv + 1;
-
-
 `ifndef COCOTB_SIM
 `ifndef VERILATOR_LINT_ONLY
 	SB_GB rst_gbuf_I (
diff --git a/gateware/cal/cal.sv b/gateware/cal/cal.sv
index 44ea2b8..14bbec2 100644
--- a/gateware/cal/cal.sv
+++ b/gateware/cal/cal.sv
@@ -26,7 +26,7 @@ module cal #(
 )(
     input rst,
     input clk_256fs,
-    input clk_fs,
+    input strobe,
     input [7:0] jack,
     input signed [W-1:0] in0,
     input signed [W-1:0] in1,
@@ -64,7 +64,6 @@ logic signed [W-1:0]     cal_mem [0:(2*N_CHANNELS)-1];
 logic signed [(2*W)-1:0] out     [N_CHANNELS];
 logic        [2:0]       ch;
 logic        [2:0]       state;
-logic                    l_clk_fs;
 
 // Calibration memory for 8 channels stored as
 // 2 bytes shift, 2 bytes multiply * 8 channels.
@@ -73,7 +72,6 @@ initial $readmemh(CAL_MEM_FILE, cal_mem);
 always_ff @(posedge clk_256fs) begin
 
     if (rst) begin
-        l_clk_fs <= 0;
         ch <= 0;
         state <= CAL_ST_LATCH;
         out[0] <= 0;
@@ -86,10 +84,7 @@ always_ff @(posedge clk_256fs) begin
         out[7] <= 0;
     end else begin
 
-        l_clk_fs <= clk_fs;
-
-        // On rising clk_fs.
-        if (clk_fs && (l_clk_fs != clk_fs)) begin
+        if (strobe) begin
             state <= CAL_ST_LATCH;
             ch <= 0;
         end else begin
diff --git a/gateware/cores/mirror.sv b/gateware/cores/mirror.sv
index bbcf5cb..76f80cb 100644
--- a/gateware/cores/mirror.sv
+++ b/gateware/cores/mirror.sv
@@ -9,7 +9,7 @@ module mirror #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
diff --git a/gateware/drivers/ak4619.sv b/gateware/drivers/ak4619.sv
index 5596a55..1d64f51 100644
--- a/gateware/drivers/ak4619.sv
+++ b/gateware/drivers/ak4619.sv
@@ -1,12 +1,10 @@
 // Driver for AK4619 CODEC.
 //
 // Usage:
-// - `clk_256fs` and `clk_fs` determine the hardware sample rate.
+// - `clk_256fs` determines the hardware sample rate.
 // - Once CODEC is initialized over I2C, samples can be streamed.
-// - `sample_in` is latched on falling `clk_fs`.
-// - `sample_out` transitions on falling `clk_fs`.
-// - As a result, users of this core should latch sample_out (and transition
-// sample_in) on rising `clk_fs`.
+// - `sample_in` is latched on `strobe`.
+// - `sample_out` transitions on `strobe`.
 //
 // This core assumes the device is configured in the audio
 // interface mode specified in ak4619-cfg.hex. This happens
@@ -28,7 +26,7 @@ module ak4619 #(
 )(
     input  rst,
     input  clk_256fs,
-    input  clk_fs,
+    input  strobe,
 
     // Route these straight out to the CODEC pins.
     output pdn,
@@ -38,13 +36,13 @@ module ak4619 #(
     output reg sdin1,
     input  sdout1,
 
-    // Transitions on falling `clk_fs`.
+    // Transitions with `strobe`.
     output reg signed [W-1:0] sample_out0,
     output reg signed [W-1:0] sample_out1,
     output reg signed [W-1:0] sample_out2,
     output reg signed [W-1:0] sample_out3,
 
-    // Latches on falling `clk_fs`.
+    // Latches with `strobe`.
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
@@ -56,7 +54,6 @@ localparam int N_CHANNELS = 4;
 logic signed [(W*N_CHANNELS)-1:0] dac_words;
 logic signed [W-1:0] adc_words [N_CHANNELS];
 
-logic last_fs;
 logic [7:0] clkdiv;
 
 logic [1:0] channel;
@@ -74,16 +71,15 @@ assign bit_counter = clkdiv[5:1];
 
 always_ff @(posedge clk_256fs) begin
     if (rst) begin
-        last_fs <= 0;
         clkdiv <= 0;
         dac_words = 0;
         sample_out0 <= 0;
         sample_out1 <= 0;
         sample_out2 <= 0;
         sample_out3 <= 0;
-    end else if (last_fs && ~clk_fs) begin
-        // Synchronize clkdiv to the incoming sample clock, latching
-        // our inputs and outputs at the falling edge of clk_fs.
+    end else if (strobe) begin
+        // Synchronize clkdiv to the incoming sample strobe, latching
+        // our inputs and outputs in the clock cycle that `strobe` is high.
         clkdiv <= 8'h0;
         dac_words = {sample_in3, sample_in2,
                      sample_in1, sample_in0};
@@ -91,7 +87,7 @@ always_ff @(posedge clk_256fs) begin
         sample_out1  <= adc_words[1];
         sample_out2  <= adc_words[2];
         sample_out3  <= adc_words[3];
-        last_fs <= clk_fs;
+        sdin1 <= dac_words[(1*W)-1];
     end else if (bick) begin
         // BICK transition HI -> LO: Clock in W bits
         // On HI -> LO both SDIN and SDOUT do not transition.
@@ -100,7 +96,6 @@ always_ff @(posedge clk_256fs) begin
             adc_words[channel][W - bit_counter - 1] <= sdout1;
         end
         clkdiv <= clkdiv + 1;
-        last_fs <= clk_fs;
     end else begin // BICK: LO -> HI
         // BICK transition LO -> HI: Clock out W bits
         // On LO -> HI both SDIN and SDOUT transition.
@@ -115,7 +110,6 @@ always_ff @(posedge clk_256fs) begin
             sdin1 <= 0;
         end
         clkdiv <= clkdiv + 1;
-        last_fs <= clk_fs;
     end
 end
 
diff --git a/gateware/eurorack_pmod.sv b/gateware/eurorack_pmod.sv
index 3a240f6..33164b8 100644
--- a/gateware/eurorack_pmod.sv
+++ b/gateware/eurorack_pmod.sv
@@ -13,7 +13,7 @@ module eurorack_pmod #(
     parameter LED_CFG_FILE  = "drivers/pca9635-cfg.hex"
 )(
     input clk_256fs,
-    input clk_fs,
+    input strobe,
     input rst,
 
     // Signals to/from eurorack-pmod hardware.
@@ -98,7 +98,7 @@ cal #(
 ) cal_instance (
     .rst(rst),
     .clk_256fs (clk_256fs),
-    .clk_fs (clk_fs),
+    .strobe (strobe),
     // Calibrated inputs are zeroed if jack is unplugged.
     .jack (jack),
     // Note: inputs samples are inverted by analog frontend
@@ -127,7 +127,7 @@ ak4619 #(
 ) ak4619_instance (
     .rst       (rst),
     .clk_256fs (clk_256fs),
-    .clk_fs    (clk_fs),
+    .strobe    (strobe),
 
     .pdn       (pdn),
     .mclk      (mclk),
diff --git a/gateware/top.sv b/gateware/top.sv
index 8a81131..a53a329 100644
--- a/gateware/top.sv
+++ b/gateware/top.sv
@@ -29,7 +29,17 @@ module top #(
 
 logic rst;
 logic clk_256fs;
-logic clk_fs; // FIXME: assign from PLL divider?
+logic strobe;
+logic [7:0] strobe_clkdiv;
+
+always_ff @(posedge clk_256fs) begin
+    if (rst) begin
+        strobe_clkdiv = 8'h0;
+    end else begin
+        strobe_clkdiv <= strobe_clkdiv + 1;
+    end
+    strobe <= (strobe_clkdiv == 8'h0);
+end
 
 // Button signal is used for resets, unless we are input calibration
 // mode in which case it is used for setting the output cal values.
@@ -90,7 +100,6 @@ sysmgr sysmgr_instance (
     .rst_in(1'b0),
 `endif
     .clk_256fs(clk_256fs),
-    .clk_fs(clk_fs),
     .rst_out(rst)
 );
 
@@ -101,7 +110,7 @@ sysmgr sysmgr_instance (
 ) dsp_core_instance (
       .rst         (rst)
     , .clk         (clk_256fs)
-    , .sample_clk  (clk_fs)
+    , .strobe      (strobe)
     , .sample_in0  (in0)
     , .sample_in1  (in1)
     , .sample_in2  (in2)
@@ -151,7 +160,7 @@ eurorack_pmod #(
     .W(W)
 ) eurorack_pmod1 (
     .clk_256fs(clk_256fs),
-    .clk_fs   (clk_fs),
+    .strobe   (strobe),
     .rst(rst),
 
     .i2c_scl_oe(i2c_scl_oe),

From 5cada7bad01a5e0639671c5fb16d198e5bcfa53e Mon Sep 17 00:00:00 2001
From: Sebastian Holzapfel <me@sebholzapfel.com>
Date: Sat, 23 Mar 2024 08:34:59 +0100
Subject: [PATCH 2/7] gateware: start updating some cores

---
 README.md                                     |  2 +-
 gateware/cores/bitcrush.sv                    | 12 ++++---
 gateware/cores/clkdiv.sv                      | 18 ++++++-----
 .../cores/{stereo_echo.sv => digital_echo.sv} | 32 ++++---------------
 gateware/cores/filter.sv                      |  4 +--
 gateware/cores/util/delayline.sv              | 19 ++++++-----
 gateware/cores/util/echo.sv                   | 14 +++++---
 .../util/filter/karlsen_lpf_pipelined.sv      |  7 ++--
 gateware/mk/common.mk                         |  2 +-
 9 files changed, 49 insertions(+), 61 deletions(-)
 rename gateware/cores/{stereo_echo.sv => digital_echo.sv} (50%)

diff --git a/README.md b/README.md
index 3803feb..2eb3795 100644
--- a/README.md
+++ b/README.md
@@ -51,7 +51,7 @@ This repository contains a bunch of example DSP cores which are continuously bei
 - `gateware/cores/clkdiv.sv` - Clock divider
 - `gateware/cores/sampler.sv` - .wav sampler
 - `gateware/cores/seqswitch.sv` - Sequential routing switch
-- `gateware/cores/stereo_echo.sv` - Echo / decimating delay effect
+- `gateware/cores/digital_echo.sv` - Echo / delay effect
 - `gateware/cores/vca.sv` - VCA (voltage controlled amplifier)
 - `gateware/cores/vco.sv` - VCO (voltage controlled oscillator)
 - `gateware/cores/bitcrush.sv` - Bitcrusher
diff --git a/gateware/cores/bitcrush.sv b/gateware/cores/bitcrush.sv
index b692808..f96fb26 100644
--- a/gateware/cores/bitcrush.sv
+++ b/gateware/cores/bitcrush.sv
@@ -14,7 +14,7 @@ module bitcrush #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
@@ -43,10 +43,12 @@ assign mask = (sample_in0 > 4*5000) ? 16'b1111111111111111 :
               (sample_in0 > 4* 500) ? 16'b1110000000000000 :
                                       16'b1100000000000000;
 
-always_ff @(posedge sample_clk) begin
-    out1 <= sample_in1 & mask;
-    out2 <= sample_in2 & mask;
-    out3 <= sample_in3 & mask;
+always_ff @(posedge clk) begin
+    if (strobe) begin
+        out1 <= sample_in1 & mask;
+        out2 <= sample_in2 & mask;
+        out3 <= sample_in3 & mask;
+    end
 end
 
 assign sample_out0 = sample_in0;
diff --git a/gateware/cores/clkdiv.sv b/gateware/cores/clkdiv.sv
index 757e973..ebc1e92 100644
--- a/gateware/cores/clkdiv.sv
+++ b/gateware/cores/clkdiv.sv
@@ -19,7 +19,7 @@ module clkdiv #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
@@ -46,13 +46,15 @@ localparam OUT_LO     = `FROM_MV(0);
 logic last_state_hi = 1'b0;
 logic [3:0] div = 0;
 
-always_ff @(posedge sample_clk) begin
-    if (sample_in0 > SCHMITT_HI && !last_state_hi) begin
-        last_state_hi <= 1'b1;
-        // Increment count on every rising edge.
-        div <= div + 1;
-    end else if (sample_in0 < SCHMITT_LO && last_state_hi) begin
-        last_state_hi <= 1'b0;
+always_ff @(posedge clk) begin
+    if (strobe) begin
+        if (sample_in0 > SCHMITT_HI && !last_state_hi) begin
+            last_state_hi <= 1'b1;
+            // Increment count on every rising edge.
+            div <= div + 1;
+        end else if (sample_in0 < SCHMITT_LO && last_state_hi) begin
+            last_state_hi <= 1'b0;
+        end
     end
 end
 
diff --git a/gateware/cores/stereo_echo.sv b/gateware/cores/digital_echo.sv
similarity index 50%
rename from gateware/cores/stereo_echo.sv
rename to gateware/cores/digital_echo.sv
index 64e0e42..ad1e217 100644
--- a/gateware/cores/stereo_echo.sv
+++ b/gateware/cores/digital_echo.sv
@@ -1,27 +1,20 @@
-// Dual digital echo effect.
+// Digital echo effect.
 //
 // Given input audio on input 0 / 1, apply a digital echo effect.
 //
 // Mapping:
 // - Input 0: Audio input 0
-// - Input 1: Audio input 1
 // - Output 0: Audio input 0 (mirrored)
 // - Output 1: Audio input 0 (echo)
-// - Output 2: Audio input 1 (mirrored)
-// - Output 3: Audio input 1 (echo)
 
-module stereo_echo #(
+module digital_echo #(
     parameter W = 16,
     // Length of the echo buffers in samples.
-    parameter ECHO_LEN = 2048,
-    // Decimate samples - this allows you to get long echo times
-    // without using all the BRAM. Effectively you end up with:
-    // ECHO_LEN (effective) = ECHO_LEN * (2 << DECIMATE)
-    parameter DECIMATE = 2
+    parameter ECHO_LEN = 4096,
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
@@ -33,26 +26,13 @@ module stereo_echo #(
     input [7:0] jack
 );
 
-logic [15:0] decimate = 0;
-logic decimate_clk = decimate[DECIMATE];
-
-always_ff @(posedge sample_clk) begin
-    decimate <= decimate + 1;
-end
-
 echo #(W, ECHO_LEN) echo0(
-    .sample_clk(decimate_clk),
+    .clk(clk),
+    .strobe(strobe),
     .sample_in(sample_in0),
     .sample_out(sample_out1)
 );
 
-echo #(W, ECHO_LEN) echo1(
-    .sample_clk(decimate_clk),
-    .sample_in(sample_in1),
-    .sample_out(sample_out3)
-);
-
 assign sample_out0 = sample_in0;
-assign sample_out2 = sample_in1;
 
 endmodule
diff --git a/gateware/cores/filter.sv b/gateware/cores/filter.sv
index 68a8d91..c4c63c5 100644
--- a/gateware/cores/filter.sv
+++ b/gateware/cores/filter.sv
@@ -13,7 +13,7 @@ module filter #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
@@ -28,7 +28,7 @@ module filter #(
 karlsen_lpf_pipelined #(.W(W)) lpf_inst(
     .rst(rst),
     .clk(clk),
-    .sample_clk(sample_clk),
+    .strobe(strobe),
     .sample_in(sample_in0),
     .sample_out(sample_out0),
     .g(sample_in1),
diff --git a/gateware/cores/util/delayline.sv b/gateware/cores/util/delayline.sv
index c557ca8..ff7e6ba 100644
--- a/gateware/cores/util/delayline.sv
+++ b/gateware/cores/util/delayline.sv
@@ -6,7 +6,8 @@ module delayline #(
     parameter W = 16,
     parameter MAX_DELAY = 1024
 )(
-    input sample_clk,
+    input clk,
+    input strobe,
     input [$clog2(MAX_DELAY)-1:0] delay,
     input signed [W-1:0] in,
     output logic signed [W-1:0] out
@@ -17,13 +18,15 @@ logic [$clog2(MAX_DELAY)-1:0] waddr = 0;
 
 logic signed [W-1:0] bram[MAX_DELAY];
 
-always_ff @(posedge sample_clk) begin
-    waddr <= waddr + 1;
-    // This subtraction wraps correctly as long as MAX_DELAY is
-    // a power of 2.
-    raddr <= waddr - delay;
-    bram[waddr] <= in;
-    out <= bram[raddr];
+always_ff @(posedge clk) begin
+    if (strobe) begin
+        waddr <= waddr + 1;
+        // This subtraction wraps correctly as long as MAX_DELAY is
+        // a power of 2.
+        raddr <= waddr - delay;
+        bram[waddr] <= in;
+        out <= bram[raddr];
+    end
 end
 
 endmodule
diff --git a/gateware/cores/util/echo.sv b/gateware/cores/util/echo.sv
index ac9fc23..6b022fb 100644
--- a/gateware/cores/util/echo.sv
+++ b/gateware/cores/util/echo.sv
@@ -4,7 +4,8 @@ module echo #(
     parameter W = 16,
     parameter ECHO_MAX_SAMPLES = 1024
 )(
-    input sample_clk,
+    input clk,
+    input strobe,
     input signed [W-1:0] sample_in,
     output logic signed [W-1:0] sample_out
 );
@@ -18,15 +19,18 @@ logic signed [W-1:0] delay_in;
 logic signed [W-1:0] delay_out;
 
 delayline #(W, ECHO_MAX_SAMPLES) delay_0 (
-    .sample_clk(sample_clk),
+    .clk(clk),
+    .strobe(strobe),
     .delay(DELAY),
     .in(delay_in),
     .out(delay_out)
 );
 
-always_ff @(posedge sample_clk) begin
-    delay_in <= (sample_in >>> 1) + (delay_out >>> FEEDBACK_SHIFT);
-    sample_out <= delay_out;
+always_ff @(posedge clk) begin
+    if (strobe) begin
+        delay_in <= (sample_in >>> 1) + (delay_out >>> FEEDBACK_SHIFT);
+        sample_out <= delay_out;
+    end
 end
 
 endmodule
diff --git a/gateware/cores/util/filter/karlsen_lpf_pipelined.sv b/gateware/cores/util/filter/karlsen_lpf_pipelined.sv
index 33912f8..395371d 100644
--- a/gateware/cores/util/filter/karlsen_lpf_pipelined.sv
+++ b/gateware/cores/util/filter/karlsen_lpf_pipelined.sv
@@ -33,7 +33,7 @@ module karlsen_lpf_pipelined #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     // See header comment for what these parameters mean.
     input signed [W-1:0] g,
     input signed [W-1:0] resonance,
@@ -49,7 +49,6 @@ localparam WMULT = 18; // Width of multiplier input
 localparam signed [WMULT-1:0] MAX = (2**(W-1))-1;
 localparam signed [WMULT-1:0] MIN = -(2**(W-1));
 
-logic prev_sample_clk;
 logic [3:0] state;
 
 logic signed [WMULT-1:0] in_ex;
@@ -72,7 +71,6 @@ assign resonance_ex = `CLAMP_POSITIVE(resonance) <<< 2;
 smul_shift_18x18 multiplier(.a(smul_a), .b(smul_b), .scale(smul_scale), .o(smul_out));
 
 always_ff @(posedge clk) begin
-    prev_sample_clk <= sample_clk;
     if (rst) begin
         state <= 0;
         a1 <= 0;
@@ -80,9 +78,8 @@ always_ff @(posedge clk) begin
         a3 <= 0;
         a4 <= 0;
         sample_out <= 0;
-        prev_sample_clk <= 0;
     end else begin
-        if (sample_clk != prev_sample_clk) begin
+        if (strobe) begin
             state <= 0;
         end else begin
             if (state < 8)
diff --git a/gateware/mk/common.mk b/gateware/mk/common.mk
index 0686490..c4fda6c 100644
--- a/gateware/mk/common.mk
+++ b/gateware/mk/common.mk
@@ -13,7 +13,7 @@ SRC_COMMON = eurorack_pmod.sv \
 		     cores/vca.sv \
 		     cores/vco.sv \
 		     cores/pitch_shift.sv \
-		     cores/stereo_echo.sv \
+		     cores/digital_echo.sv \
 		     cores/filter.sv \
 		     cores/touch_cv.sv \
 		     cores/util/filter/karlsen_lpf_pipelined.sv \

From 4a3c1287173ea05f23249ad0e67f908f8191b56f Mon Sep 17 00:00:00 2001
From: Sebastian Holzapfel <me@sebholzapfel.com>
Date: Sat, 23 Mar 2024 08:35:30 +0100
Subject: [PATCH 3/7] hacks for testing

---
 gateware/cal/cal_mem_default_r31.hex       |  4 ++--
 gateware/sim/ak4619/tb_ak4619.py           | 27 +++++++++++++---------
 gateware/sim/integration/tb_integration.py |  5 +++-
 3 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/gateware/cal/cal_mem_default_r31.hex b/gateware/cal/cal_mem_default_r31.hex
index ea8c880..3dd92ec 100644
--- a/gateware/cal/cal_mem_default_r31.hex
+++ b/gateware/cal/cal_mem_default_r31.hex
@@ -1,4 +1,4 @@
 // Input calibration constants
-@00000000 11c0 650 10b2 64f 114a 650 1134 64f
+@00000000 0 400 0 400 0 400 0 400
 // Output calibration constants
-@00000008 f6e 3ed e53 3ef f3d 3ee fa0 3ef
+@00000008 0 400 0 400 0 400 0 400
diff --git a/gateware/sim/ak4619/tb_ak4619.py b/gateware/sim/ak4619/tb_ak4619.py
index ac01ebe..fc229ce 100644
--- a/gateware/sim/ak4619/tb_ak4619.py
+++ b/gateware/sim/ak4619/tb_ak4619.py
@@ -11,33 +11,38 @@
 @cocotb.test()
 async def test_ak4619_00(dut):
 
-    clk_256fs = Clock(dut.clk_256fs, 83, units='ns')
-    clk_fs = Clock(dut.clk_fs, 83*256, units='ns')
-    cocotb.start_soon(clk_256fs.start())
-    cocotb.start_soon(clk_fs.start(start_high=False))
-
     TEST_L0 = 0xFC140000
     TEST_R0 = 0xAD0F0000
     TEST_L1 = 0xDEAD0000
     TEST_R1 = 0xBEEF0000
 
-    dut.sdout1.value = 0
+    clk_256fs = Clock(dut.clk_256fs, 83, units='ns')
+    cocotb.start_soon(clk_256fs.start())
 
+    dut.strobe.value = 0
+    dut.sdout1.value = 0
     dut.rst.value = 1
+
+    async def strobe():
+        while True:
+            dut.strobe.value = 1
+            await ClockCycles(dut.clk_256fs, 1)
+            dut.strobe.value = 0
+            await ClockCycles(dut.clk_256fs, 255)
+
     await RisingEdge(dut.clk_256fs)
     await RisingEdge(dut.clk_256fs)
     dut.rst.value = 0
 
-    await FallingEdge(dut.lrck)
-    await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_L0)
-    await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_R0)
+    cocotb.start_soon(strobe())
     await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_L1)
     await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_R1)
+    await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_L0)
+    await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_R0)
 
     # Note: this edge is also where dac_words <= sample_in (sample.sv)
 
-    await RisingEdge(dut.clk_fs)
-    await FallingEdge(dut.clk_fs)
+    await RisingEdge(dut.clk_256fs)
     print("Data clocked from sdout1 present at sample_outX:")
     print(hex(dut.sample_out0.value.integer))
     print(hex(dut.sample_out1.value.integer))
diff --git a/gateware/sim/integration/tb_integration.py b/gateware/sim/integration/tb_integration.py
index df36e95..a9666c5 100644
--- a/gateware/sim/integration/tb_integration.py
+++ b/gateware/sim/integration/tb_integration.py
@@ -29,13 +29,16 @@ async def test_integration_00(dut):
     await RisingEdge(dut.clk_256fs)
     dut.sysmgr_instance.pll_lock.value = 1
 
+    await FallingEdge(dut.strobe)
+    await FallingEdge(dut.strobe)
+
     ak4619 = dut.eurorack_pmod1.ak4619_instance
 
     N = 20
 
     for i in range(N):
 
-        v = bits_from_signed(int(16000*math.sin((2*math.pi*i)/N)), sample_width)
+        v = bits_from_signed(0x00FF, sample_width)#int(16000*math.sin((2*math.pi*i)/N)), sample_width)
 
         await FallingEdge(ak4619.lrck)
 

From 0eee31d66ace3e760de19392ce1d0f805ea3eab8 Mon Sep 17 00:00:00 2001
From: Sebastian Holzapfel <me@sebholzapfel.com>
Date: Wed, 12 Jun 2024 16:12:13 +0200
Subject: [PATCH 4/7] cores: verify all cores work on icebreaker

---
 gateware/cores/bitcrush.sv           |  4 +-
 gateware/cores/pitch_shift.sv        |  5 +-
 gateware/cores/sampler.sv            | 34 +++++++-------
 gateware/cores/seqswitch.sv          | 69 ++++++++++++++--------------
 gateware/cores/touch_cv.sv           |  2 +-
 gateware/cores/util/transpose.sv     | 51 ++++++++++----------
 gateware/cores/util/wavetable_osc.sv | 19 ++++----
 gateware/cores/vca.sv                |  2 +-
 gateware/cores/vco.sv                | 23 ++++++----
 gateware/top.sv                      |  2 +-
 10 files changed, 114 insertions(+), 97 deletions(-)

diff --git a/gateware/cores/bitcrush.sv b/gateware/cores/bitcrush.sv
index f96fb26..acc9366 100644
--- a/gateware/cores/bitcrush.sv
+++ b/gateware/cores/bitcrush.sv
@@ -27,6 +27,7 @@ module bitcrush #(
 );
 
 logic signed [W-1:0] mask;
+logic signed [W-1:0] out0;
 logic signed [W-1:0] out1;
 logic signed [W-1:0] out2;
 logic signed [W-1:0] out3;
@@ -45,13 +46,14 @@ assign mask = (sample_in0 > 4*5000) ? 16'b1111111111111111 :
 
 always_ff @(posedge clk) begin
     if (strobe) begin
+        out0 <= sample_in0;
         out1 <= sample_in1 & mask;
         out2 <= sample_in2 & mask;
         out3 <= sample_in3 & mask;
     end
 end
 
-assign sample_out0 = sample_in0;
+assign sample_out0 = out0;
 assign sample_out1 = out1;
 assign sample_out2 = out2;
 assign sample_out3 = out3;
diff --git a/gateware/cores/pitch_shift.sv b/gateware/cores/pitch_shift.sv
index 6d22b99..b576308 100644
--- a/gateware/cores/pitch_shift.sv
+++ b/gateware/cores/pitch_shift.sv
@@ -14,7 +14,7 @@ module pitch_shift #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
@@ -29,7 +29,8 @@ module pitch_shift #(
 transpose #(
     .W(W)
 ) transpose_instance (
-    .sample_clk(sample_clk),
+    .clk,
+    .strobe,
     .pitch(sample_in1),
     .sample_in(sample_in0),
     .sample_out(sample_out1)
diff --git a/gateware/cores/sampler.sv b/gateware/cores/sampler.sv
index d430a13..7712e5a 100644
--- a/gateware/cores/sampler.sv
+++ b/gateware/cores/sampler.sv
@@ -18,7 +18,7 @@ module sampler #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
@@ -46,21 +46,23 @@ logic [$clog2(N_SAMPLES):0] sample_pos = 0;
 // Value of the last sample at sample_pos, synchronized to sample_clk.
 logic [W-1:0] cur_sample = 16'h0;
 
-always_ff @(posedge sample_clk) begin
-    sclkdiv <= sclkdiv + 1;
-    if (sclkdiv % 2 == 0 && sample_pos <= N_SAMPLES) begin
-        sample_pos <= sample_pos + 1;
-    end
-    if (sample_in0 < TRIGGER_HI) begin
-        // Hold first sample as long as we have no trigger. As
-        // soon as it goes high, we 'allow' playback.
-        sample_pos <= 0;
-    end
-    if (sample_pos < N_SAMPLES) begin
-        cur_sample <= wav_samples[sample_pos[$clog2(N_SAMPLES)-1:0]];
-    end else begin
-        // If we go past the end of the sample, hold 0V at the output.
-        cur_sample <= 16'h0;
+always_ff @(posedge clk) begin
+    if (strobe) begin
+        sclkdiv <= sclkdiv + 1;
+        if (sclkdiv % 2 == 0 && sample_pos <= N_SAMPLES) begin
+            sample_pos <= sample_pos + 1;
+        end
+        if (sample_in0 < TRIGGER_HI) begin
+            // Hold first sample as long as we have no trigger. As
+            // soon as it goes high, we 'allow' playback.
+            sample_pos <= 0;
+        end
+        if (sample_pos < N_SAMPLES) begin
+            cur_sample <= wav_samples[sample_pos[$clog2(N_SAMPLES)-1:0]];
+        end else begin
+            // If we go past the end of the sample, hold 0V at the output.
+            cur_sample <= 16'h0;
+        end
     end
 end
 
diff --git a/gateware/cores/seqswitch.sv b/gateware/cores/seqswitch.sv
index ee86c64..aa78e44 100644
--- a/gateware/cores/seqswitch.sv
+++ b/gateware/cores/seqswitch.sv
@@ -18,7 +18,7 @@ module seqswitch #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
@@ -43,43 +43,44 @@ logic last_state_hi = 1'b0;
 // Current routing state of the sequential switch.
 logic [1:0] switch_state = 2'b00;
 
-always_ff @(posedge sample_clk) begin
+always_ff @(posedge clk) begin
+    if (strobe) begin
+        // Rising edge of clock.
+        if (sample_in0 > SCHMITT_HI && !last_state_hi) begin
+            last_state_hi <= 1'b1;
 
-    // Rising edge of clock.
-    if (sample_in0 > SCHMITT_HI && !last_state_hi) begin
-        last_state_hi <= 1'b1;
+            // Update switch routing on a rising edge.
+            if (switch_state == 2'b10) switch_state <= 2'b00;
+            else switch_state <= switch_state + 1;
+        end
 
-        // Update switch routing on a rising edge.
-        if (switch_state == 2'b10) switch_state <= 2'b00;
-        else switch_state <= switch_state + 1;
-    end
+        // Falling edge of clock.
+        if (sample_in0 < SCHMITT_LO && last_state_hi) begin
+            last_state_hi <= 1'b0;
+        end
 
-    // Falling edge of clock.
-    if (sample_in0 < SCHMITT_LO && last_state_hi) begin
-        last_state_hi <= 1'b0;
+        // Samples mirrored at audio rate based on current routing.
+        case (switch_state)
+            2'b00: begin
+                sample_out1 <= sample_in1;
+                sample_out2 <= sample_in2;
+                sample_out3 <= sample_in3;
+            end
+            2'b01: begin
+                sample_out1 <= sample_in2;
+                sample_out2 <= sample_in3;
+                sample_out3 <= sample_in1;
+            end
+            2'b10: begin
+                sample_out1 <= sample_in3;
+                sample_out2 <= sample_in1;
+                sample_out3 <= sample_in2;
+            end
+            default: begin
+                // State is never entered
+            end
+        endcase
     end
-
-    // Samples mirrored at audio rate based on current routing.
-    case (switch_state)
-        2'b00: begin
-            sample_out1 <= sample_in1;
-            sample_out2 <= sample_in2;
-            sample_out3 <= sample_in3;
-        end
-        2'b01: begin
-            sample_out1 <= sample_in2;
-            sample_out2 <= sample_in3;
-            sample_out3 <= sample_in1;
-        end
-        2'b10: begin
-            sample_out1 <= sample_in3;
-            sample_out2 <= sample_in1;
-            sample_out3 <= sample_in2;
-        end
-        default: begin
-            // State is never entered
-        end
-    endcase
 end
 
 assign sample_out0 = sample_in0;
diff --git a/gateware/cores/touch_cv.sv b/gateware/cores/touch_cv.sv
index 5662176..e8044df 100644
--- a/gateware/cores/touch_cv.sv
+++ b/gateware/cores/touch_cv.sv
@@ -15,7 +15,7 @@ module touch_cv #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
diff --git a/gateware/cores/util/transpose.sv b/gateware/cores/util/transpose.sv
index e1feed5..84b2efd 100644
--- a/gateware/cores/util/transpose.sv
+++ b/gateware/cores/util/transpose.sv
@@ -13,7 +13,8 @@ module transpose #(
     parameter WINDOW = 512,
     parameter XFADE = 128
 )(
-    input sample_clk,
+    input clk,
+    input strobe,
     input signed [W-1:0] pitch,
     input signed [W-1:0] sample_in,
     output logic signed [W-1:0] sample_out
@@ -43,42 +44,46 @@ logic signed [XFADE_BITS:0] env1_reg;
 // have no interpolation between integer delay line steps.
 
 delayline #(W, DELAYLINE_LEN) delay_0 (
-    .sample_clk(sample_clk),
+    .clk,
+    .strobe,
     .delay({1'b0, delay_int}),
     .in(sample_in),
     .out(delay_out0)
 );
 
 delayline #(W, DELAYLINE_LEN) delay_1(
-    .sample_clk(sample_clk),
+    .clk,
+    .strobe,
     .delay({1'b0, delay_int}+WINDOW),
     .in(sample_in),
     .out(delay_out1)
 );
 
-always_ff @(posedge sample_clk) begin
-    // The value we increment `d` by here is actually the 'pitch shift' amount.
-    // walking up the delay lines some amount faster or slower than usual.
-    //
-    // TODO: Make this track 1V/oct.
-    delay_frac <= delay_frac + (pitch >>> 8);
+always_ff @(posedge clk) begin
+    if (strobe) begin
+        // The value we increment `d` by here is actually the 'pitch shift' amount.
+        // walking up the delay lines some amount faster or slower than usual.
+        //
+        // TODO: Make this track 1V/oct.
+        delay_frac <= delay_frac + (pitch >>> 8);
 
-    if (delay_int < XFADE) begin
-        env0 <= delay_int[XFADE_BITS:0];
-        env1 <= (XFADE-1) - delay_int[XFADE_BITS:0];
-    end else begin
-        env0 <= XFADE-1;
-        env1 <= 0;
-    end
+        if (delay_int < XFADE) begin
+            env0 <= delay_int[XFADE_BITS:0];
+            env1 <= (XFADE-1) - delay_int[XFADE_BITS:0];
+        end else begin
+            env0 <= XFADE-1;
+            env1 <= 0;
+        end
 
-    // Envelopes need to be delayed by 1 sample to avoid discontinuity as we
-    // swap between the 2 delay line feeds.
-    env0_reg <= env0;
-    env1_reg <= env1;
+        // Envelopes need to be delayed by 1 sample to avoid discontinuity as we
+        // swap between the 2 delay line feeds.
+        env0_reg <= env0;
+        env1_reg <= env1;
 
-    // TODO: pipeline these multiplies.
-    sample_out <= W'(((W+XFADE_BITS)'(delay_out0) * (W+XFADE_BITS)'(env0_reg)) >>> XFADE_BITS) +
-                  W'(((W+XFADE_BITS)'(delay_out1) * (W+XFADE_BITS)'(env1_reg)) >>> XFADE_BITS);
+        // TODO: pipeline these multiplies.
+        sample_out <= W'(((W+XFADE_BITS)'(delay_out0) * (W+XFADE_BITS)'(env0_reg)) >>> XFADE_BITS) +
+                      W'(((W+XFADE_BITS)'(delay_out1) * (W+XFADE_BITS)'(env1_reg)) >>> XFADE_BITS);
+    end
 end
 
 endmodule
diff --git a/gateware/cores/util/wavetable_osc.sv b/gateware/cores/util/wavetable_osc.sv
index e570b5f..134b130 100644
--- a/gateware/cores/util/wavetable_osc.sv
+++ b/gateware/cores/util/wavetable_osc.sv
@@ -5,7 +5,8 @@ module wavetable_osc #(
     parameter WAVETABLE_SIZE = 256
 )(
     input rst,
-    input sample_clk,
+    input clk,
+    input strobe,
     input [31:0] wavetable_inc,
     output logic signed [W-1:0] out
 );
@@ -16,13 +17,15 @@ initial $readmemh(WAVETABLE_PATH, wavetable);
 // Position in wavetable - N.F fixed-point where BIT_START is size of F.
 logic [31:0] wavetable_pos = 0;
 
-always_ff @(posedge sample_clk) begin
-    if (rst) begin
-        wavetable_pos <= 0;
-    end else begin
-        wavetable_pos <= wavetable_pos + wavetable_inc;
-        // Take top N bits of wavetable_pos as output.
-        out <= wavetable[wavetable_pos[FRAC_BITS+$clog2(WAVETABLE_SIZE)-1:FRAC_BITS]];
+always_ff @(posedge clk) begin
+    if (strobe) begin
+        if (rst) begin
+            wavetable_pos <= 0;
+        end else begin
+            wavetable_pos <= wavetable_pos + wavetable_inc;
+            // Take top N bits of wavetable_pos as output.
+            out <= wavetable[wavetable_pos[FRAC_BITS+$clog2(WAVETABLE_SIZE)-1:FRAC_BITS]];
+        end
     end
 end
 
diff --git a/gateware/cores/vca.sv b/gateware/cores/vca.sv
index 647cdce..1435139 100644
--- a/gateware/cores/vca.sv
+++ b/gateware/cores/vca.sv
@@ -19,7 +19,7 @@ module vca #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
diff --git a/gateware/cores/vco.sv b/gateware/cores/vco.sv
index 0fab58b..7ac914b 100644
--- a/gateware/cores/vco.sv
+++ b/gateware/cores/vco.sv
@@ -15,7 +15,7 @@ module vco #(
 )(
     input rst,
     input clk,
-    input sample_clk,
+    input strobe,
     input signed [W-1:0] sample_in0,
     input signed [W-1:0] sample_in1,
     input signed [W-1:0] sample_in2,
@@ -39,13 +39,15 @@ initial $readmemh(V_OCT_LUT_PATH, v_oct_lut);
 logic signed [W-1:0] lut_index = 0;
 logic signed [W-1:0] lut_index_clamp_lo = 0;
 
-always_ff @(posedge sample_clk) begin
-    if (rst) begin
-        lut_index <= 0;
-        lut_index_clamp_lo <= 0;
-    end else begin
-        lut_index <= sample_in0 >>> 6;
-        lut_index_clamp_lo <= lut_index < 0 ? 0 : lut_index;
+always_ff @(posedge clk) begin
+    if (strobe) begin
+        if (rst) begin
+            lut_index <= 0;
+            lut_index_clamp_lo <= 0;
+        end else begin
+            lut_index <= sample_in0 >>> 6;
+            lut_index_clamp_lo <= lut_index < 0 ? 0 : lut_index;
+        end
     end
 end
 
@@ -55,8 +57,9 @@ wavetable_osc #(
     .WAVETABLE_PATH(WAVETABLE_PATH),
     .WAVETABLE_SIZE(WAVETABLE_SIZE)
 ) osc_0 (
-    .rst(rst),
-    .sample_clk(sample_clk),
+    .rst,
+    .clk,
+    .strobe,
     .wavetable_inc(32'(v_oct_lut[$clog2(V_OCT_LUT_SIZE)'(lut_index_clamp_lo)])),
     .out(sample_out0)
 );
diff --git a/gateware/top.sv b/gateware/top.sv
index a53a329..2ff10f4 100644
--- a/gateware/top.sv
+++ b/gateware/top.sv
@@ -34,7 +34,7 @@ logic [7:0] strobe_clkdiv;
 
 always_ff @(posedge clk_256fs) begin
     if (rst) begin
-        strobe_clkdiv = 8'h0;
+        strobe_clkdiv <= 8'h0;
     end else begin
         strobe_clkdiv <= strobe_clkdiv + 1;
     end

From a74dcf7a2c0bc73ff4828c203d0b31df3dc0d769 Mon Sep 17 00:00:00 2001
From: Sebastian Holzapfel <me@sebholzapfel.com>
Date: Wed, 12 Jun 2024 16:21:04 +0200
Subject: [PATCH 5/7] gateware: switch from clk_fs to strobe on all boards.
 verify ecpix also works

---
 gateware/boards/colorlight_i5/sysmgr.v | 9 ---------
 gateware/boards/ecpix5/sysmgr.v        | 9 ---------
 gateware/boards/gatemate_evb/sysmgr.v  | 9 ---------
 gateware/boards/pico_ice/sysmgr.v      | 9 ---------
 gateware/cores/digital_echo.sv         | 2 +-
 gateware/scripts/verilator_lint.sh     | 2 +-
 6 files changed, 2 insertions(+), 38 deletions(-)

diff --git a/gateware/boards/colorlight_i5/sysmgr.v b/gateware/boards/colorlight_i5/sysmgr.v
index fd194ba..40418ba 100644
--- a/gateware/boards/colorlight_i5/sysmgr.v
+++ b/gateware/boards/colorlight_i5/sysmgr.v
@@ -5,7 +5,6 @@ module sysmgr (
 	input  wire clk_in,
 	input  wire rst_in,
 	output wire clk_256fs,
-	output wire clk_fs,
 	output wire rst_out
 );
 
@@ -15,12 +14,10 @@ wire pll_reset;
 wire rst_i;
 
 reg [7:0] rst_cnt;
-reg [7:0] clkdiv;
 
 assign pll_reset = rst_in;
 assign rst_i = ~rst_cnt[7];
 assign rst_out = rst_i;
-assign clk_fs = clkdiv[7];
 
 `ifndef VERILATOR_LINT_ONLY
 
@@ -75,10 +72,4 @@ always @(posedge clk_in)
     else if (~rst_cnt[7])
         rst_cnt <= rst_cnt + 1;
 
-always @(posedge clk_256fs)
-    if (rst_i)
-        clkdiv <= 8'h00;
-    else
-        clkdiv <= clkdiv + 1;
-
 endmodule // sysmgr
diff --git a/gateware/boards/ecpix5/sysmgr.v b/gateware/boards/ecpix5/sysmgr.v
index c9c3340..02954ef 100644
--- a/gateware/boards/ecpix5/sysmgr.v
+++ b/gateware/boards/ecpix5/sysmgr.v
@@ -5,7 +5,6 @@ module sysmgr (
 	input  wire clk_in,
 	input  wire rst_in,
 	output wire clk_256fs,
-	output wire clk_fs,
 	output wire rst_out
 );
 
@@ -15,12 +14,10 @@ wire pll_reset;
 wire rst_i;
 
 reg [7:0] rst_cnt;
-reg [7:0] clkdiv;
 
 assign rst_i = ~rst_cnt[7];
 assign rst_out = rst_i;
 assign pll_reset = rst_in;
-assign clk_fs = clkdiv[7];
 
 `ifndef VERILATOR_LINT_ONLY
 
@@ -71,10 +68,4 @@ always @(posedge clk_in)
     else if (~rst_cnt[7])
         rst_cnt <= rst_cnt + 1;
 
-always @(posedge clk_256fs)
-    if (rst_i)
-        clkdiv <= 8'h00;
-    else
-        clkdiv <= clkdiv + 1;
-
 endmodule // sysmgr
diff --git a/gateware/boards/gatemate_evb/sysmgr.v b/gateware/boards/gatemate_evb/sysmgr.v
index 1117e04..7615e0e 100644
--- a/gateware/boards/gatemate_evb/sysmgr.v
+++ b/gateware/boards/gatemate_evb/sysmgr.v
@@ -4,7 +4,6 @@ module sysmgr (
 	input  wire clk_in,
 	input  wire rst_in,
 	output wire clk_256fs,
-	output wire clk_fs,
 	output wire rst_out
 );
 
@@ -14,12 +13,10 @@ wire pll_reset;
 wire rst_i;
 
 reg [7:0] rst_cnt;
-reg [7:0] clkdiv;
 
 assign pll_reset = rst_in;
 assign rst_i = ~rst_cnt[7];
 assign rst_out = rst_i;
-assign clk_fs = clkdiv[7];
 
 `ifndef VERILATOR_LINT_ONLY
 
@@ -46,10 +43,4 @@ always @(posedge clk_in)
     else if (~rst_cnt[7])
         rst_cnt <= rst_cnt + 1;
 
-always @(posedge clk_256fs)
-    if (rst_i)
-        clkdiv <= 8'h00;
-    else
-        clkdiv <= clkdiv + 1;
-
 endmodule // sysmgr
diff --git a/gateware/boards/pico_ice/sysmgr.v b/gateware/boards/pico_ice/sysmgr.v
index 83cbeed..09a6b57 100644
--- a/gateware/boards/pico_ice/sysmgr.v
+++ b/gateware/boards/pico_ice/sysmgr.v
@@ -3,7 +3,6 @@
 module sysmgr (
 	input  wire rst_in,
 	output wire clk_256fs,
-	output wire clk_fs,
 	output wire rst_out
 );
 
@@ -11,10 +10,8 @@ module sysmgr (
 	wire rst_i;
 
 	reg [7:0] rst_cnt = 8'h80;
-    reg [7:0] clkdiv;
 
     assign clk_256fs = clk_12m;
-    assign clk_fs = clkdiv[7];
 	assign rst_i = rst_cnt[7];
 
 `ifndef VERILATOR_LINT_ONLY
@@ -35,12 +32,6 @@ module sysmgr (
 		else if (rst_cnt[7])
 			rst_cnt <= rst_cnt + 1;
 
-    always @(posedge clk_256fs)
-        if (rst_i)
-            clkdiv <= 8'h00;
-        else
-            clkdiv <= clkdiv + 1;
-
 `ifndef VERILATOR_LINT_ONLY
 	SB_GB rst_gbuf_I (
 		.USER_SIGNAL_TO_GLOBAL_BUFFER(rst_i),
diff --git a/gateware/cores/digital_echo.sv b/gateware/cores/digital_echo.sv
index ad1e217..80d650d 100644
--- a/gateware/cores/digital_echo.sv
+++ b/gateware/cores/digital_echo.sv
@@ -10,7 +10,7 @@
 module digital_echo #(
     parameter W = 16,
     // Length of the echo buffers in samples.
-    parameter ECHO_LEN = 4096,
+    parameter ECHO_LEN = 4096
 )(
     input rst,
     input clk,
diff --git a/gateware/scripts/verilator_lint.sh b/gateware/scripts/verilator_lint.sh
index 2c63734..5416ee1 100755
--- a/gateware/scripts/verilator_lint.sh
+++ b/gateware/scripts/verilator_lint.sh
@@ -56,6 +56,6 @@ verilator --lint-only cores/util/filter/karlsen_lpf.sv
 verilator --lint-only cores/util/filter/karlsen_lpf_pipelined.sv
 verilator --lint-only -Icores -Icores/util/filter filter.sv
 verilator --lint-only -Icores -Icores/util pitch_shift.sv
-verilator --lint-only -Icores -Icores/util stereo_echo.sv
+verilator --lint-only -Icores -Icores/util digital_echo.sv
 verilator --lint-only -Icores -Icores/util dc_block.sv
 verilator --lint-only -Icores -Icores/util wavetable_osc.sv

From 4f8faa60cb312e32d1158ee728602d86a1090743 Mon Sep 17 00:00:00 2001
From: Sebastian Holzapfel <me@sebholzapfel.com>
Date: Wed, 12 Jun 2024 17:43:52 +0200
Subject: [PATCH 6/7] gateware/sim: update testbenches for s/clk_fs/strobe

---
 gateware/drivers/ak4619.sv                 | 15 +++++------
 gateware/sim/ak4619/tb_ak4619.py           | 29 +++++++++-------------
 gateware/sim/cal/tb_cal.py                 | 21 +++++++++++-----
 gateware/sim/integration/tb_integration.py |  9 +++----
 gateware/sim/transpose/tb_transpose.py     | 22 ++++++++++------
 gateware/sim/vca/tb_vca.py                 | 20 ++++++++++-----
 6 files changed, 66 insertions(+), 50 deletions(-)

diff --git a/gateware/drivers/ak4619.sv b/gateware/drivers/ak4619.sv
index 1d64f51..56fcfef 100644
--- a/gateware/drivers/ak4619.sv
+++ b/gateware/drivers/ak4619.sv
@@ -71,18 +71,19 @@ assign bit_counter = clkdiv[5:1];
 
 always_ff @(posedge clk_256fs) begin
     if (rst) begin
+        sdin1 <= 0;
         clkdiv <= 0;
-        dac_words = 0;
-        sample_out0 <= 0;
-        sample_out1 <= 0;
-        sample_out2 <= 0;
-        sample_out3 <= 0;
+        adc_words[0] <= 0;
+        adc_words[1] <= 0;
+        adc_words[2] <= 0;
+        adc_words[3] <= 0;
+        dac_words <= 0;
     end else if (strobe) begin
         // Synchronize clkdiv to the incoming sample strobe, latching
         // our inputs and outputs in the clock cycle that `strobe` is high.
         clkdiv <= 8'h0;
-        dac_words = {sample_in3, sample_in2,
-                     sample_in1, sample_in0};
+        dac_words <= {sample_in3, sample_in2,
+                      sample_in1, sample_in0};
         sample_out0  <= adc_words[0];
         sample_out1  <= adc_words[1];
         sample_out2  <= adc_words[2];
diff --git a/gateware/sim/ak4619/tb_ak4619.py b/gateware/sim/ak4619/tb_ak4619.py
index fc229ce..7e18e34 100644
--- a/gateware/sim/ak4619/tb_ak4619.py
+++ b/gateware/sim/ak4619/tb_ak4619.py
@@ -19,6 +19,10 @@ async def test_ak4619_00(dut):
     clk_256fs = Clock(dut.clk_256fs, 83, units='ns')
     cocotb.start_soon(clk_256fs.start())
 
+    dut.sample_in0.value = Force(0)
+    dut.sample_in1.value = Force(0)
+    dut.sample_in2.value = Force(0)
+    dut.sample_in3.value = Force(0)
     dut.strobe.value = 0
     dut.sdout1.value = 0
     dut.rst.value = 1
@@ -35,14 +39,13 @@ async def strobe():
     dut.rst.value = 0
 
     cocotb.start_soon(strobe())
-    await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_L1)
-    await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_R1)
     await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_L0)
     await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_R0)
+    await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_L1)
+    await i2s_clock_out_u32(dut.bick, dut.sdout1, TEST_R1)
 
-    # Note: this edge is also where dac_words <= sample_in (sample.sv)
+    await FallingEdge(dut.strobe)
 
-    await RisingEdge(dut.clk_256fs)
     print("Data clocked from sdout1 present at sample_outX:")
     print(hex(dut.sample_out0.value.integer))
     print(hex(dut.sample_out1.value.integer))
@@ -59,8 +62,7 @@ async def strobe():
     dut.sample_in2.value = Force(TEST_L1 >> 16)
     dut.sample_in3.value = Force(TEST_R1 >> 16)
 
-    await FallingEdge(dut.lrck)
-    await FallingEdge(dut.lrck)
+    await RisingEdge(dut.strobe)
 
     result_l0 = await i2s_clock_in_u32(dut.bick, dut.sdin1)
     result_r0 = await i2s_clock_in_u32(dut.bick, dut.sdin1)
@@ -73,14 +75,7 @@ async def strobe():
     print(hex(result_l1))
     print(hex(result_r1))
 
-    assert result_l0 == TEST_L0
-    assert result_r0 == TEST_R0
-    assert result_l1 == TEST_L1
-    assert result_r1 == TEST_R1
-
-    dut.sample_in0.value = Release()
-    dut.sample_in1.value = Release()
-    dut.sample_in2.value = Release()
-    dut.sample_in3.value = Release()
-
-    await FallingEdge(dut.clk_fs)
+    assert result_l0 & 0xFFFFFF00 == TEST_L0
+    assert result_r0 & 0xFFFFFF00 == TEST_R0
+    assert result_l1 & 0xFFFFFF00 == TEST_L1
+    assert result_r1 & 0xFFFFFF00 == TEST_R1
diff --git a/gateware/sim/cal/tb_cal.py b/gateware/sim/cal/tb_cal.py
index 0efccfb..c055c0a 100644
--- a/gateware/sim/cal/tb_cal.py
+++ b/gateware/sim/cal/tb_cal.py
@@ -14,13 +14,24 @@ async def test_cal_00(dut):
     sample_width = 16
 
     clk_256fs = Clock(dut.clk_256fs, 83, units='ns')
-    clk_fs = Clock(dut.clk_fs, 83*256, units='ns')
     cocotb.start_soon(clk_256fs.start())
-    cocotb.start_soon(clk_fs.start(start_high=False))
 
     # Simulate all jacks connected so the cal core doesn't zero them
     dut.jack.value = Force(0xFF)
 
+    # Add 1/256 sample strobe
+    dut.strobe.value = 0
+    async def strobe():
+        while True:
+            dut.strobe.value = 1
+            await ClockCycles(dut.clk_256fs, 1)
+            dut.strobe.value = 0
+            await ClockCycles(dut.clk_256fs, 255)
+    await RisingEdge(dut.clk_256fs)
+    await RisingEdge(dut.clk_256fs)
+    dut.rst.value = 0
+    cocotb.start_soon(strobe())
+
     clampl = -2**(sample_width-1) + 1
     clamph =  2**(sample_width-1) - 1;
 
@@ -65,10 +76,8 @@ async def test_cal_00(dut):
             if expect >  clamph: expect = clamph
             if expect < clampl: expect = clampl
             print(f"ch={channel}\t{int(value):6d}\t", end="")
-            await FallingEdge(dut.clk_fs)
-            await RisingEdge(dut.clk_fs)
-            await RisingEdge(dut.clk_fs)
-            await RisingEdge(dut.clk_fs)
+            await RisingEdge(dut.strobe)
+            await RisingEdge(dut.strobe)
             output = signed_from_bits(cal_outx.value, sample_width)
             print(f"=>\t{int(output):6d}\t(expect={expect})")
             cal_inx.value = Release()
diff --git a/gateware/sim/integration/tb_integration.py b/gateware/sim/integration/tb_integration.py
index a9666c5..c9d39a7 100644
--- a/gateware/sim/integration/tb_integration.py
+++ b/gateware/sim/integration/tb_integration.py
@@ -29,18 +29,15 @@ async def test_integration_00(dut):
     await RisingEdge(dut.clk_256fs)
     dut.sysmgr_instance.pll_lock.value = 1
 
-    await FallingEdge(dut.strobe)
-    await FallingEdge(dut.strobe)
-
     ak4619 = dut.eurorack_pmod1.ak4619_instance
 
+    await FallingEdge(dut.strobe)
+
     N = 20
 
     for i in range(N):
 
-        v = bits_from_signed(0x00FF, sample_width)#int(16000*math.sin((2*math.pi*i)/N)), sample_width)
-
-        await FallingEdge(ak4619.lrck)
+        v = bits_from_signed(int(16000*math.sin((2*math.pi*i)/N)), sample_width)
 
         await i2s_clock_out_u32(ak4619.bick, ak4619.sdout1, v << 16)
         await i2s_clock_out_u32(ak4619.bick, ak4619.sdout1, v << 16)
diff --git a/gateware/sim/transpose/tb_transpose.py b/gateware/sim/transpose/tb_transpose.py
index 253caf6..80fa743 100644
--- a/gateware/sim/transpose/tb_transpose.py
+++ b/gateware/sim/transpose/tb_transpose.py
@@ -16,12 +16,18 @@ async def test_transpose_00(dut):
 
     sample_width = 16
 
-    clock = Clock(dut.sample_clk, 5, units='us')
-    cocotb.start_soon(clock.start())
-
-    # Not needed at the moment as we aren't pipelining things
-    #clock = Clock(dut.clk, 83, units='ns')
-    #cocotb.start_soon(clock.start())
+    clk_256fs = Clock(dut.clk, 83, units='ns')
+    cocotb.start_soon(clk_256fs.start())
+
+    # Add 1/256 sample strobe
+    dut.strobe.value = 0
+    async def strobe():
+        while True:
+            dut.strobe.value = 1
+            await ClockCycles(dut.clk, 1)
+            dut.strobe.value = 0
+            await ClockCycles(dut.clk, 255)
+    cocotb.start_soon(strobe())
 
     dut.sample_in.value = 0
     dut.pitch.value = 5000*4
@@ -29,7 +35,7 @@ async def test_transpose_00(dut):
     # Clock in some zeroes so the delay lines are full of zeroes.
 
     for i in range(1024):
-        await RisingEdge(dut.sample_clk)
+        await RisingEdge(dut.strobe)
 
     # Stimulate the pitch shifter with a sine wave and make sure
     # the output does not have any discontinuities
@@ -38,7 +44,7 @@ async def test_transpose_00(dut):
     breaknext = False
 
     for i in range(2048):
-        await RisingEdge(dut.sample_clk)
+        await RisingEdge(dut.strobe)
 
         data_in = int(1000*math.sin(i / 100))
 
diff --git a/gateware/sim/vca/tb_vca.py b/gateware/sim/vca/tb_vca.py
index 6afcc48..8937da4 100644
--- a/gateware/sim/vca/tb_vca.py
+++ b/gateware/sim/vca/tb_vca.py
@@ -14,17 +14,25 @@ async def test_vca_00(dut):
 
     sample_width=16
 
-    clock = Clock(dut.sample_clk, 5, units='us')
-    cocotb.start_soon(clock.start())
-    clock = Clock(dut.clk, 83, units='ns')
-    cocotb.start_soon(clock.start())
+    clk_256fs = Clock(dut.clk, 83, units='ns')
+    cocotb.start_soon(clk_256fs.start())
+
+    # Add 1/256 sample strobe
+    dut.strobe.value = 0
+    async def strobe():
+        while True:
+            dut.strobe.value = 1
+            await ClockCycles(dut.clk, 1)
+            dut.strobe.value = 0
+            await ClockCycles(dut.clk, 255)
+    cocotb.start_soon(strobe())
 
     ins  = [dut.sample_in0,  dut.sample_in1,  dut.sample_in2,  dut.sample_in3]
     outs = [dut.sample_out0, dut.sample_out1, dut.sample_out2, dut.sample_out3]
 
     for i in range(10):
 
-        await RisingEdge(dut.sample_clk)
+        await RisingEdge(dut.strobe)
 
         data_in = []
         for inx in ins:
@@ -32,7 +40,7 @@ async def test_vca_00(dut):
             data_in.append(random_sample)
             inx.value = bits_from_signed(random_sample, sample_width)
 
-        await RisingEdge(dut.sample_clk)
+        await RisingEdge(dut.strobe)
 
         data_out = [signed_from_bits(out.value, sample_width) for out in outs]
 

From a5b88e6b725a2c320f89abdda8770f9b6798d9fb Mon Sep 17 00:00:00 2001
From: Sebastian Holzapfel <me@sebholzapfel.com>
Date: Wed, 12 Jun 2024 17:47:07 +0200
Subject: [PATCH 7/7] gateware/cal: revert r31 cal_mem change

---
 gateware/cal/cal_mem_default_r31.hex | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gateware/cal/cal_mem_default_r31.hex b/gateware/cal/cal_mem_default_r31.hex
index 3dd92ec..ea8c880 100644
--- a/gateware/cal/cal_mem_default_r31.hex
+++ b/gateware/cal/cal_mem_default_r31.hex
@@ -1,4 +1,4 @@
 // Input calibration constants
-@00000000 0 400 0 400 0 400 0 400
+@00000000 11c0 650 10b2 64f 114a 650 1134 64f
 // Output calibration constants
-@00000008 0 400 0 400 0 400 0 400
+@00000008 f6e 3ed e53 3ef f3d 3ee fa0 3ef