diff --git a/fpga/lib/eth/README.md b/fpga/lib/eth/README.md
index 9e7a73fe1..ac882ebab 100644
--- a/fpga/lib/eth/README.md
+++ b/fpga/lib/eth/README.md
@@ -289,8 +289,8 @@ nanoseconds field.
 ### ptp_clock_cdc module
 
 PTP clock CDC module with PPS output.  Use this module to transfer and deskew a
-free-running PTP clock across clock domains.  Currently supports 96 bit
-timestamps.
+free-running PTP clock across clock domains.  Supports both 64 and 96 bit
+timestamp formats.
 
 ### ptp_ts_extract module
 
diff --git a/fpga/lib/eth/rtl/ptp_clock_cdc.v b/fpga/lib/eth/rtl/ptp_clock_cdc.v
index baac193a4..aa0a1395a 100644
--- a/fpga/lib/eth/rtl/ptp_clock_cdc.v
+++ b/fpga/lib/eth/rtl/ptp_clock_cdc.v
@@ -68,8 +68,8 @@ module ptp_clock_cdc #
 
 // bus width assertions
 initial begin
-    if (TS_WIDTH != 96) begin
-        $error("Error: Timestamp width must be 96");
+    if (TS_WIDTH != 64 && TS_WIDTH != 96) begin
+        $error("Error: Timestamp width must be 64 or 96");
         $finish;
     end
 end
@@ -330,7 +330,7 @@ reg sec_mismatch_reg = 1'b0;
 reg diff_valid_reg = 1'b0;
 reg diff_offset_valid_reg = 1'b0;
 
-reg [30:0] ts_ns_diff_reg = 31'd0;
+reg [TS_NS_WIDTH+1-1:0] ts_ns_diff_reg = 31'd0;
 reg [FNS_WIDTH-1:0] ts_fns_diff_reg = 16'd0;
 
 reg [48:0] time_err_int_reg = 32'd0;
@@ -342,45 +342,71 @@ always @(posedge output_clk) begin
     diff_offset_valid_reg <= 1'b0;
 
     // 96 bit timestamp
-    if (!ts_ns_ovf_reg[30]) begin
-        // if the overflow lookahead did not borrow, one second has elapsed
-        // increment seconds field, pre-compute both normal increment and overflow values
-        {ts_ns_inc_reg, ts_fns_inc_reg} <= {ts_ns_ovf_reg, ts_fns_ovf_reg} + {period_ns_reg, period_fns_reg};
-        {ts_ns_ovf_reg, ts_fns_ovf_reg} <= {ts_ns_ovf_reg, ts_fns_ovf_reg} + {period_ns_reg, period_fns_reg} - {31'd1_000_000_000, {FNS_WIDTH{1'b0}}};
-        {ts_ns_reg, ts_fns_reg} <= {ts_ns_ovf_reg, ts_fns_ovf_reg};
-        ts_s_reg <= ts_s_reg + 1;
-    end else begin
-        // no increment seconds field, pre-compute both normal increment and overflow values
-        {ts_ns_inc_reg, ts_fns_inc_reg} <= {ts_ns_inc_reg, ts_fns_inc_reg} + {period_ns_reg, period_fns_reg};
-        {ts_ns_ovf_reg, ts_fns_ovf_reg} <= {ts_ns_inc_reg, ts_fns_inc_reg} + {period_ns_reg, period_fns_reg} - {31'd1_000_000_000, {FNS_WIDTH{1'b0}}};
-        {ts_ns_reg, ts_fns_reg} <= {ts_ns_inc_reg, ts_fns_inc_reg};
-        ts_s_reg <= ts_s_reg;
+    if (TS_WIDTH == 96) begin
+        if (!ts_ns_ovf_reg[30]) begin
+            // if the overflow lookahead did not borrow, one second has elapsed
+            // increment seconds field, pre-compute both normal increment and overflow values
+            {ts_ns_inc_reg, ts_fns_inc_reg} <= {ts_ns_ovf_reg, ts_fns_ovf_reg} + {period_ns_reg, period_fns_reg};
+            {ts_ns_ovf_reg, ts_fns_ovf_reg} <= {ts_ns_ovf_reg, ts_fns_ovf_reg} + {period_ns_reg, period_fns_reg} - {31'd1_000_000_000, {FNS_WIDTH{1'b0}}};
+            {ts_ns_reg, ts_fns_reg} <= {ts_ns_ovf_reg, ts_fns_ovf_reg};
+            ts_s_reg <= ts_s_reg + 1;
+        end else begin
+            // no increment seconds field, pre-compute both normal increment and overflow values
+            {ts_ns_inc_reg, ts_fns_inc_reg} <= {ts_ns_inc_reg, ts_fns_inc_reg} + {period_ns_reg, period_fns_reg};
+            {ts_ns_ovf_reg, ts_fns_ovf_reg} <= {ts_ns_inc_reg, ts_fns_inc_reg} + {period_ns_reg, period_fns_reg} - {31'd1_000_000_000, {FNS_WIDTH{1'b0}}};
+            {ts_ns_reg, ts_fns_reg} <= {ts_ns_inc_reg, ts_fns_inc_reg};
+            ts_s_reg <= ts_s_reg;
+        end
+    end else if (TS_WIDTH == 64) begin
+        {ts_ns_reg, ts_fns_reg} <= {ts_ns_reg, ts_fns_reg} + {period_ns_reg, period_fns_reg};
     end
 
     // FIFO dequeue
     if (read) begin
         // dequeue from FIFO
-        if (mem_read_data_reg[95:48] != ts_s_reg) begin
-            // seconds field doesn't match
-            if (!sec_mismatch_reg) begin
-                // ignore the first time
-                sec_mismatch_reg <= 1'b1;
-            end else begin
-                // two seconds mismatches in a row; step the clock
-                sec_mismatch_reg <= 1'b0;
+        if (TS_WIDTH == 96) begin
+            if (mem_read_data_reg[95:48] != ts_s_reg) begin
+                // seconds field doesn't match
+                if (!sec_mismatch_reg) begin
+                    // ignore the first time
+                    sec_mismatch_reg <= 1'b1;
+                end else begin
+                    // two seconds mismatches in a row; step the clock
+                    sec_mismatch_reg <= 1'b0;
 
-                {ts_ns_inc_reg, ts_fns_inc_reg} <= (FNS_WIDTH > 16 ? mem_read_data_reg[45:0] << (FNS_WIDTH-16) : mem_read_data_reg[45:0] >> (16-FNS_WIDTH)) + {period_ns_reg, period_fns_reg};
-                {ts_ns_ovf_reg, ts_fns_ovf_reg} <= (FNS_WIDTH > 16 ? mem_read_data_reg[45:0] << (FNS_WIDTH-16) : mem_read_data_reg[45:0] >> (16-FNS_WIDTH)) + {period_ns_reg, period_fns_reg} - {31'd1_000_000_000, {FNS_WIDTH{1'b0}}};
-                ts_s_reg <= mem_read_data_reg[95:48];
-                ts_ns_reg <= mem_read_data_reg[45:16];
-                ts_fns_reg <= FNS_WIDTH > 16 ? mem_read_data_reg[15:0] << (FNS_WIDTH-16) : mem_read_data_reg[15:0] >> (16-FNS_WIDTH);
-                ts_step_reg <= 1;
+                    {ts_ns_inc_reg, ts_fns_inc_reg} <= (FNS_WIDTH > 16 ? mem_read_data_reg[45:0] << (FNS_WIDTH-16) : mem_read_data_reg[45:0] >> (16-FNS_WIDTH)) + {period_ns_reg, period_fns_reg};
+                    {ts_ns_ovf_reg, ts_fns_ovf_reg} <= (FNS_WIDTH > 16 ? mem_read_data_reg[45:0] << (FNS_WIDTH-16) : mem_read_data_reg[45:0] >> (16-FNS_WIDTH)) + {period_ns_reg, period_fns_reg} - {31'd1_000_000_000, {FNS_WIDTH{1'b0}}};
+                    ts_s_reg <= mem_read_data_reg[95:48];
+                    ts_ns_reg <= mem_read_data_reg[45:16];
+                    ts_fns_reg <= FNS_WIDTH > 16 ? mem_read_data_reg[15:0] << (FNS_WIDTH-16) : mem_read_data_reg[15:0] >> (16-FNS_WIDTH);
+                    ts_step_reg <= 1;
+                end
+            end else begin
+                // compute difference
+                sec_mismatch_reg <= 1'b0;
+                diff_valid_reg <= 1'b1;
+                {ts_ns_diff_reg, ts_fns_diff_reg} <= {ts_ns_reg, ts_fns_reg} - (FNS_WIDTH > 16 ? mem_read_data_reg[45:0] << (FNS_WIDTH-16) : mem_read_data_reg[45:0] >> (16-FNS_WIDTH));
+            end
+        end else if (TS_WIDTH == 64) begin
+            if (mem_read_data_reg[63:48] != ts_ns_reg[47:32]) begin
+                // high-order bits don't match
+                if (!sec_mismatch_reg) begin
+                    // ignore the first time
+                    sec_mismatch_reg <= 1'b1;
+                end else begin
+                    // two seconds mismatches in a row; step the clock
+                    sec_mismatch_reg <= 1'b0;
+
+                    ts_ns_reg <= mem_read_data_reg[63:16];
+                    ts_fns_reg <= FNS_WIDTH > 16 ? mem_read_data_reg[15:0] << (FNS_WIDTH-16) : mem_read_data_reg[15:0] >> (16-FNS_WIDTH);
+                    ts_step_reg <= 1;
+                end
+            end else begin
+                // compute difference
+                sec_mismatch_reg <= 1'b0;
+                diff_valid_reg <= 1'b1;
+                {ts_ns_diff_reg, ts_fns_diff_reg} <= {ts_ns_reg, ts_fns_reg} - (FNS_WIDTH > 16 ? mem_read_data_reg[63:0] << (FNS_WIDTH-16) : mem_read_data_reg[63:0] >> (16-FNS_WIDTH));
             end
-        end else begin
-            // compute difference
-            sec_mismatch_reg <= 1'b0;
-            diff_valid_reg <= 1'b1;
-            {ts_ns_diff_reg, ts_fns_diff_reg} <= {ts_ns_reg, ts_fns_reg} - (FNS_WIDTH > 16 ? mem_read_data_reg[45:0] << (FNS_WIDTH-16) : mem_read_data_reg[45:0] >> (16-FNS_WIDTH));
         end
     end else if (diff_valid_reg) begin
         // offset difference by FIFO delay
@@ -404,7 +430,11 @@ always @(posedge output_clk) begin
         end
     end
 
-    pps_reg <= !ts_ns_ovf_reg[30];
+    if (TS_WIDTH == 96) begin
+        pps_reg <= !ts_ns_ovf_reg[30];
+    end else if (TS_WIDTH == 64) begin
+        pps_reg <= 1'b0; // not currently implemented for 64 bit timestamp format
+    end
 
     if (output_rst) begin
         period_ns_reg <= OUTPUT_PERIOD_NS;
@@ -414,7 +444,7 @@ always @(posedge output_clk) begin
         ts_fns_reg <= 0;
         ts_ns_inc_reg <= 0;
         ts_fns_inc_reg <= 0;
-        ts_ns_ovf_reg <= 31'h7fffffff;
+        ts_ns_ovf_reg <= {TS_NS_WIDTH{1'b1}};
         ts_fns_ovf_reg <= {FNS_WIDTH{1'b1}};
         ts_step_reg <= 0;
         pps_reg <= 0;
diff --git a/fpga/lib/eth/tb/test_ptp_clock_cdc_64.py b/fpga/lib/eth/tb/test_ptp_clock_cdc_64.py
new file mode 100755
index 000000000..79746c69a
--- /dev/null
+++ b/fpga/lib/eth/tb/test_ptp_clock_cdc_64.py
@@ -0,0 +1,246 @@
+#!/usr/bin/env python
+"""
+
+Copyright (c) 2019 Alex Forencich
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+
+"""
+
+from myhdl import *
+import os
+
+import ptp
+
+module = 'ptp_clock_cdc'
+testbench = 'test_%s_64' % module
+
+srcs = []
+
+srcs.append("../rtl/%s.v" % module)
+srcs.append("%s.v" % testbench)
+
+src = ' '.join(srcs)
+
+build_cmd = "iverilog -o %s.vvp %s" % (testbench, src)
+
+def bench():
+
+    # Parameters
+    TS_WIDTH = 64
+    NS_WIDTH = 4
+    FNS_WIDTH = 16
+    INPUT_PERIOD_NS = 0x6
+    INPUT_PERIOD_FNS = 0x6666
+    OUTPUT_PERIOD_NS = 0x6
+    OUTPUT_PERIOD_FNS = 0x6666
+    USE_SAMPLE_CLOCK = 1
+    LOG_FIFO_DEPTH = 3
+    LOG_RATE = 3
+
+    # Inputs
+    clk = Signal(bool(0))
+    rst = Signal(bool(0))
+    current_test = Signal(intbv(0)[8:])
+
+    input_clk = Signal(bool(0))
+    input_rst = Signal(bool(0))
+    output_clk = Signal(bool(0))
+    output_rst = Signal(bool(0))
+    sample_clk = Signal(bool(0))
+    input_ts = Signal(intbv(0)[96:])
+
+    # Outputs
+    output_ts = Signal(intbv(0)[96:])
+    output_ts_step = Signal(bool(0))
+    output_pps = Signal(bool(0))
+
+    # PTP clock
+    ptp_clock = ptp.PtpClock()
+
+    ptp_logic = ptp_clock.create_logic(
+        input_clk,
+        input_rst,
+        ts_64=input_ts
+    )
+
+    # DUT
+    if os.system(build_cmd):
+        raise Exception("Error running build command")
+
+    dut = Cosimulation(
+        "vvp -m myhdl %s.vvp -lxt2" % testbench,
+        clk=clk,
+        rst=rst,
+        current_test=current_test,
+        input_clk=input_clk,
+        input_rst=input_rst,
+        output_clk=output_clk,
+        output_rst=output_rst,
+        sample_clk=sample_clk,
+        input_ts=input_ts,
+        output_ts=output_ts,
+        output_ts_step=output_ts_step,
+        output_pps=output_pps
+    )
+
+    @always(delay(3200))
+    def clkgen():
+        clk.next = not clk
+        input_clk.next = not input_clk
+
+    output_clk_hp = Signal(int(3200))
+
+    @instance
+    def clkgen_output():
+        while True:
+            yield delay(int(output_clk_hp))
+            output_clk.next = not output_clk
+
+    @always(delay(5000))
+    def clkgen_sample():
+        sample_clk.next = not sample_clk
+
+    @instance
+    def check():
+        yield delay(100000)
+        yield clk.posedge
+        rst.next = 1
+        input_rst.next = 1
+        output_rst.next = 1
+        yield clk.posedge
+        yield clk.posedge
+        yield clk.posedge
+        input_rst.next = 0
+        output_rst.next = 0
+        yield clk.posedge
+        yield delay(100000)
+        yield clk.posedge
+
+        # testbench stimulus
+
+        yield clk.posedge
+        print("test 1: Same clock speed")
+        current_test.next = 1
+
+        yield clk.posedge
+
+        for i in range(20000):
+            yield clk.posedge
+
+        input_stop_ts = input_ts/2**16*1e-9
+        output_stop_ts = output_ts/2**16*1e-9
+
+        print(input_stop_ts-output_stop_ts)
+
+        assert abs(input_stop_ts-output_stop_ts) < 1e-8
+
+        yield delay(100000)
+
+        yield clk.posedge
+        print("test 2: Slightly faster")
+        current_test.next = 2
+
+        output_clk_hp.next = 3100
+
+        yield clk.posedge
+
+        for i in range(20000):
+            yield clk.posedge
+
+        input_stop_ts = input_ts/2**16*1e-9
+        output_stop_ts = output_ts/2**16*1e-9
+
+        print(input_stop_ts-output_stop_ts)
+
+        assert abs(input_stop_ts-output_stop_ts) < 1e-8
+
+        yield delay(100000)
+
+        yield clk.posedge
+        print("test 3: Slightly slower")
+        current_test.next = 3
+
+        output_clk_hp.next = 3300
+
+        yield clk.posedge
+
+        for i in range(20000):
+            yield clk.posedge
+
+        input_stop_ts = input_ts/2**16*1e-9
+        output_stop_ts = output_ts/2**16*1e-9
+
+        print(input_stop_ts-output_stop_ts)
+
+        assert abs(input_stop_ts-output_stop_ts) < 1e-8
+
+        yield delay(100000)
+
+        yield clk.posedge
+        print("test 4: Significantly faster")
+        current_test.next = 4
+
+        output_clk_hp.next = 2000
+
+        yield clk.posedge
+
+        for i in range(20000):
+            yield clk.posedge
+
+        input_stop_ts = input_ts/2**16*1e-9
+        output_stop_ts = output_ts/2**16*1e-9
+
+        print(input_stop_ts-output_stop_ts)
+
+        assert abs(input_stop_ts-output_stop_ts) < 1e-8
+
+        yield delay(100000)
+
+        yield clk.posedge
+        print("test 5: Significantly slower")
+        current_test.next = 5
+
+        output_clk_hp.next = 5000
+
+        yield clk.posedge
+
+        for i in range(30000):
+            yield clk.posedge
+
+        input_stop_ts = input_ts/2**16*1e-9
+        output_stop_ts = output_ts/2**16*1e-9
+
+        print(input_stop_ts-output_stop_ts)
+
+        assert abs(input_stop_ts-output_stop_ts) < 1e-8
+
+        yield delay(100000)
+
+        raise StopSimulation
+
+    return instances()
+
+def test_bench():
+    sim = Simulation(bench())
+    sim.run()
+
+if __name__ == '__main__':
+    print("Running test...")
+    test_bench()
diff --git a/fpga/lib/eth/tb/test_ptp_clock_cdc_64.v b/fpga/lib/eth/tb/test_ptp_clock_cdc_64.v
new file mode 100644
index 000000000..777d12cd8
--- /dev/null
+++ b/fpga/lib/eth/tb/test_ptp_clock_cdc_64.v
@@ -0,0 +1,111 @@
+/*
+
+Copyright (c) 2019 Alex Forencich
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+
+*/
+
+// Language: Verilog 2001
+
+`timescale 1ps / 1fs
+
+/*
+ * Testbench for ptp_clock_cdc
+ */
+module test_ptp_clock_cdc_64;
+
+// Parameters
+parameter TS_WIDTH = 64;
+parameter NS_WIDTH = 4;
+parameter FNS_WIDTH = 16;
+parameter INPUT_PERIOD_NS = 4'h6;
+parameter INPUT_PERIOD_FNS = 16'h6666;
+parameter OUTPUT_PERIOD_NS = 4'h6;
+parameter OUTPUT_PERIOD_FNS = 16'h6666;
+parameter USE_SAMPLE_CLOCK = 1;
+parameter LOG_FIFO_DEPTH = 3;
+parameter LOG_RATE = 3;
+
+// Inputs
+reg clk = 0;
+reg rst = 0;
+reg [7:0] current_test = 0;
+
+reg input_clk = 0;
+reg input_rst = 0;
+reg output_clk = 0;
+reg output_rst = 0;
+reg sample_clk = 0;
+reg [TS_WIDTH-1:0] input_ts = 0;
+
+// Outputs
+wire [TS_WIDTH-1:0] output_ts;
+wire output_ts_step;
+wire output_pps;
+
+initial begin
+    // myhdl integration
+    $from_myhdl(
+        clk,
+        rst,
+        current_test,
+        input_clk,
+        input_rst,
+        output_clk,
+        output_rst,
+        sample_clk,
+        input_ts
+    );
+    $to_myhdl(
+        output_ts,
+        output_ts_step,
+        output_pps
+    );
+
+    // dump file
+    $dumpfile("test_ptp_clock_cdc_64.lxt");
+    $dumpvars(0, test_ptp_clock_cdc_64);
+end
+
+ptp_clock_cdc #(
+    .TS_WIDTH(TS_WIDTH),
+    .NS_WIDTH(NS_WIDTH),
+    .FNS_WIDTH(FNS_WIDTH),
+    .INPUT_PERIOD_NS(INPUT_PERIOD_NS),
+    .INPUT_PERIOD_FNS(INPUT_PERIOD_FNS),
+    .OUTPUT_PERIOD_NS(OUTPUT_PERIOD_NS),
+    .OUTPUT_PERIOD_FNS(OUTPUT_PERIOD_FNS),
+    .USE_SAMPLE_CLOCK(USE_SAMPLE_CLOCK),
+    .LOG_FIFO_DEPTH(LOG_FIFO_DEPTH),
+    .LOG_RATE(LOG_RATE)
+)
+UUT (
+    .input_clk(input_clk),
+    .input_rst(input_rst),
+    .output_clk(output_clk),
+    .output_rst(output_rst),
+    .sample_clk(sample_clk),
+    .input_ts(input_ts),
+    .output_ts(output_ts),
+    .output_ts_step(output_ts_step),
+    .output_pps(output_pps)
+);
+
+endmodule