diff --git a/config_d/registers b/config_d/registers
index 752da7a..e108ec0 100755
--- a/config_d/registers
+++ b/config_d/registers
@@ -55,6 +55,10 @@ BLOCKS_COMPAT_VERSION = 0
     # frequency of 125 MHz will be reported and used.
     NOMINAL_CLOCK           24
 
+    # Hardware timestamps
+    PCAP_TS_SEC             25
+    PCAP_TS_NSEC            26
+
 
 # These registers are used by the kernel driver to read the data capture stream.
 # This block is not used by the server, but is here for documentation and other
diff --git a/server/data_server.c b/server/data_server.c
index 8e00644..8427677 100644
--- a/server/data_server.c
+++ b/server/data_server.c
@@ -101,6 +101,7 @@ static const struct data_capture *data_capture;
 static struct timespec pcap_arm_ts;
 /* PCAP becomes armed & enabled timestamp */
 static struct timespec pcap_start_ts;
+static int64_t pcap_hw_ts_offset;
 
 /* Data completion code at end of experiment. */
 static unsigned int completion_code;
@@ -108,6 +109,30 @@ static unsigned int completion_code;
 static uint64_t experiment_sample_count;
 
 
+/* Save start timestamp, either from hardware (if that timestamp is not 0), or
+ * from the driver (which was saved in the interrupt handler triggered by the
+ * start event) */
+static void update_start_timestamp(void)
+{
+    struct timespec pcap_drv_start_ts, pcap_hw_start_ts;
+    hw_get_start_ts(&pcap_drv_start_ts);
+    hw_get_hw_start_ts(&pcap_hw_start_ts);
+    if (pcap_hw_start_ts.tv_sec == 0 && pcap_hw_start_ts.tv_nsec == 0) {
+        pcap_start_ts = pcap_drv_start_ts;
+        pcap_hw_ts_offset = 0;
+    } else {
+        int64_t drv_ts_num =
+            (int64_t) pcap_drv_start_ts.tv_sec * 1000000000
+            + pcap_drv_start_ts.tv_nsec;
+        int64_t hw_ts_num =
+            (int64_t) pcap_hw_start_ts.tv_sec * 1000000000
+            + pcap_hw_start_ts.tv_nsec;
+        pcap_start_ts = pcap_hw_start_ts;
+        pcap_hw_ts_offset = drv_ts_num - hw_ts_num;
+    }
+}
+
+
 /* Performs a complete experiment capture: start data buffer, process the data
  * stream until hardware is complete, stop data buffer. */
 static void capture_experiment(void)
@@ -135,7 +160,7 @@ static void capture_experiment(void)
          * timestamp, that's how it goes. */
         if (!ts_captured)
         {
-            hw_get_start_ts(&pcap_start_ts);
+            update_start_timestamp();
             ts_captured = true;
         }
 
@@ -687,7 +712,7 @@ error__t process_data_socket(int scon)
                 ok = send_data_header(
                     captured_fields, data_capture,
                     &connection.options, connection.file, lost_samples,
-                    &pcap_arm_ts, &pcap_start_ts);
+                    &pcap_arm_ts, &pcap_start_ts, pcap_hw_ts_offset);
 
             uint64_t sent_samples = 0;
             if (ok)
diff --git a/server/hardware.c b/server/hardware.c
index 96c18d1..251c5e8 100644
--- a/server/hardware.c
+++ b/server/hardware.c
@@ -324,6 +324,13 @@ void hw_get_start_ts(struct timespec *ts)
     ts->tv_nsec = (typeof(ts->tv_nsec)) compat_ts.tv_nsec;
 }
 
+
+void hw_get_hw_start_ts(struct timespec *ts)
+{
+    ts->tv_sec = (time_t) read_named_register(PCAP_TS_SEC);
+    ts->tv_nsec = (typeof(ts->tv_nsec)) read_named_register(PCAP_TS_NSEC);
+}
+
 #endif
 
 
diff --git a/server/hardware.h b/server/hardware.h
index bf4d2a0..2ee761b 100644
--- a/server/hardware.h
+++ b/server/hardware.h
@@ -166,6 +166,8 @@ const char *hw_decode_completion(unsigned int completion);
 
 /* This function gets the timestamp when PCAP becomes armed and enabled */
 void hw_get_start_ts(struct timespec *ts);
+/* This one is latched in hardware instead of the driver */
+void hw_get_hw_start_ts(struct timespec *ts);
 
 /* This function controls the arm/disarm state of data capture.  Data capture is
  * armed by writing true with this function, after which hw_read_streamed_data()
diff --git a/server/prepare.c b/server/prepare.c
index 3496afa..f86f5ed 100644
--- a/server/prepare.c
+++ b/server/prepare.c
@@ -278,7 +278,7 @@ static void send_capture_info(
     struct buffered_file *file,
     const struct data_capture *capture, const struct data_options *options,
     uint64_t missed_samples, struct timespec *pcap_arm_tsp,
-    struct timespec *pcap_start_tsp)
+    struct timespec *pcap_start_tsp, int64_t pcap_hw_ts_offset)
 {
     static const char *data_format_strings[] = {
         [DATA_FORMAT_UNFRAMED] = "Unframed",
@@ -303,6 +303,7 @@ static void send_capture_info(
     format_timestamp_message(
         timestamp_message, MAX_RESULT_LENGTH, pcap_start_tsp);
     format_attribute(&element, "start_time", "%s", timestamp_message);
+    format_attribute(&element, "hw_time_offset", "%"PRIi64, pcap_hw_ts_offset);
     format_attribute(&element, "missed", "%"PRIu64, missed_samples);
     format_attribute(&element, "process", "%s", data_process);
     format_attribute(&element, "format", "%s", data_format);
@@ -377,13 +378,15 @@ bool send_data_header(
     const struct data_capture *capture,
     const struct data_options *options,
     struct buffered_file *file, uint64_t missed_samples,
-    struct timespec *pcap_arm_tsp, struct timespec *pcap_start_tsp)
+    struct timespec *pcap_arm_tsp, struct timespec *pcap_start_tsp,
+    int64_t pcap_hw_ts_offset)
 {
     struct xml_element header =
         start_element(file, "header", options->xml_header, true, true);
 
     send_capture_info(
-        file, capture, options, missed_samples, pcap_arm_tsp, pcap_start_tsp);
+        file, capture, options, missed_samples, pcap_arm_tsp, pcap_start_tsp,
+        pcap_hw_ts_offset);
 
     /* Format the field capture descriptions. */
     struct xml_element field_group =
diff --git a/server/prepare.h b/server/prepare.h
index b75c26d..6f5e36d 100644
--- a/server/prepare.h
+++ b/server/prepare.h
@@ -46,7 +46,8 @@ bool send_data_header(
     const struct data_capture *capture,
     const struct data_options *options,
     struct buffered_file *file, uint64_t lost_samples,
-    struct timespec *pcap_arm_tsp, struct timespec *pcap_start_tsp);
+    struct timespec *pcap_arm_tsp, struct timespec *pcap_start_tsp,
+    int64_t pcap_hw_ts_offset);
 
 
 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
diff --git a/server/sim_hardware.c b/server/sim_hardware.c
index 057a247..2450778 100644
--- a/server/sim_hardware.c
+++ b/server/sim_hardware.c
@@ -188,6 +188,13 @@ void hw_get_start_ts(struct timespec *ts)
 }
 
 
+void hw_get_hw_start_ts(struct timespec *ts)
+{
+    ts->tv_sec = 0;
+    ts->tv_nsec = 0;
+}
+
+
 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 /* Long table support. */