diff --git a/hw/ip/usbdev/rtl/usbdev.sv b/hw/ip/usbdev/rtl/usbdev.sv
index dbb7404..de36a30 100644
--- a/hw/ip/usbdev/rtl/usbdev.sv
+++ b/hw/ip/usbdev/rtl/usbdev.sv
@@ -136,7 +136,7 @@
   logic              usb_event_rx_bitstuff_err;
   logic              usb_event_in_err;
   logic              usb_event_out_err;
-  logic              usb_event_frame;
+  logic              usb_event_frame, usb_event_sof;
   logic              usb_link_active;
 
   logic              event_link_reset, event_link_suspend, event_link_resume;
@@ -585,6 +585,7 @@
     // status
     .frame_o              (usb_frame),
     .frame_start_o        (usb_event_frame),
+    .sof_valid_o          (usb_event_sof),
     .link_state_o         (usb_link_state),
     .link_disconnect_o    (usb_event_disconnect),
     .link_powered_o       (usb_event_powered),
@@ -1080,7 +1081,7 @@
   );
 
   // Directly forward the pulse unless disabled.
-  assign usb_ref_pulse_o = usb_ref_disable ? 1'b0 : usb_event_frame;
+  assign usb_ref_pulse_o = usb_ref_disable ? 1'b0 : usb_event_sof;
 
   // The first pulse is always ignored, but causes the valid to be asserted.
   // The valid signal is deasserted when:
diff --git a/hw/ip/usbdev/rtl/usbdev_linkstate.sv b/hw/ip/usbdev/rtl/usbdev_linkstate.sv
index 4108925..2b28f8b 100644
--- a/hw/ip/usbdev/rtl/usbdev_linkstate.sv
+++ b/hw/ip/usbdev/rtl/usbdev_linkstate.sv
@@ -28,6 +28,7 @@
   output logic link_suspend_o,     // level
   output logic link_resume_o,      // pulse
   output logic host_lost_o,        // level
+  output logic sof_missed_o,       // pulse
 
   output logic [2:0] link_state_o
 );
@@ -38,6 +39,10 @@
   // confuse the 2 *low-speed* bit times (1.33us) of SE0 that terminate resume
   // signaling. Use 3us here.
   localparam logic [2:0]  RESET_TIMEOUT   = 3'd3;
+  // Consider an SOF lost after 1.005 ms. The extra 5 us helps accommodate
+  // the worst case frequency difference between the host and device, due to a
+  // +/- 2500 ppm range around 12 MHz.
+  localparam logic [9:0]  SOF_TIMEOUT     = 10'd1005;
 
   typedef enum logic [2:0] {
     // No power and/or no pull-up connected state
@@ -349,24 +354,37 @@
     end
   end
 
-  /////////////////////////
-  // Host loss detection //
-  /////////////////////////
-  // host_lost if no sof in 4.096ms (supposed to be every 1ms)
-  // and the link is active
-  logic [12:0] host_presence_timer;
+  /////////////////////////////////////////
+  // Host loss and missing sof detection //
+  /////////////////////////////////////////
+  // sof_missed if no SOF was observed in 1.005ms and the link is active
+  // host_lost if 4 frames have gone by without observing a SOF
+  logic [2:0] missed_sof_count;
+  logic [9:0] missing_sof_timer;
 
-  assign host_lost_o = host_presence_timer[12];
+  assign host_lost_o = missed_sof_count[2];
   always_ff @(posedge clk_48mhz_i or negedge rst_ni) begin
     if (!rst_ni) begin
-      host_presence_timer <= '0;
+      missed_sof_count <= '0;
     end else begin
       if (sof_valid_i || !link_active_o || link_reset) begin
-        host_presence_timer <= '0;
-      end else if (us_tick_i && !host_lost_o) begin
-        host_presence_timer <= host_presence_timer + 1;
+        missed_sof_count <= '0;
+      end else if (sof_missed_o && !host_lost_o) begin
+        missed_sof_count <= missed_sof_count + '1;
       end
     end
   end
 
+  assign sof_missed_o = (missing_sof_timer == SOF_TIMEOUT);
+  always_ff @(posedge clk_48mhz_i or negedge rst_ni) begin
+    if (!rst_ni) begin
+      missing_sof_timer <= '0;
+    end else begin
+      if (sof_missed_o || sof_valid_i || !link_active_o || link_reset) begin
+        missing_sof_timer <= '0;
+      end else if (us_tick_i) begin
+        missing_sof_timer <= missing_sof_timer + 1;
+      end
+    end
+  end
 endmodule
diff --git a/hw/ip/usbdev/rtl/usbdev_usbif.sv b/hw/ip/usbdev/rtl/usbdev_usbif.sv
index e1eca63..790cc4d 100644
--- a/hw/ip/usbdev/rtl/usbdev_usbif.sv
+++ b/hw/ip/usbdev/rtl/usbdev_usbif.sv
@@ -82,8 +82,10 @@
   input  logic                     resume_link_active_i, // Jump from LinkPowered to LinkResuming
 
   // status
-  output logic                     frame_start_o,
+  output logic                     frame_start_o, // Pulses with host-generated and internal SOF
   output logic [10:0]              frame_o,
+  output logic                     sof_valid_o, // Pulses with only host-generated SOF.
+                                                // Used for clock sync.
   output logic [2:0]               link_state_o,
   output logic                     link_disconnect_o,
   output logic                     link_powered_o,
@@ -116,7 +118,6 @@
   logic                              mem_read;
   logic [SramAw-1:0]                 mem_waddr, mem_raddr;
   logic                              link_reset;
-  logic                              sof_valid;
 
   // Make sure out_endpoint_o can safely be used to index signals of NEndpoints width.
   assign out_endpoint_val_o = int'(out_ep_current) < NEndpoints;
@@ -124,7 +125,6 @@
 
   assign link_reset_o   = link_reset;
   assign clr_devaddr_o  = ~enable_i | link_reset;
-  assign frame_start_o  = sof_valid;
   assign link_out_err_o = out_ep_rollback;
 
   always_comb begin
@@ -329,13 +329,14 @@
     .rx_bitstuff_err_o     (rx_bitstuff_err_o),
 
     // sof interface
-    .sof_valid_o           (sof_valid),
+    .sof_valid_o           (sof_valid_o),
     .frame_index_o         (frame_index_raw)
   );
 
   // us_tick ticks for one cycle every us
   logic [5:0]   ns_cnt;
   logic         us_tick;
+  logic         do_internal_sof;
 
   assign us_tick = (ns_cnt == 6'd48);
   always_ff @(posedge clk_48mhz_i or negedge rst_ni) begin
@@ -350,15 +351,27 @@
     end
   end
 
-  // Capture frame number (host sends evert 1ms)
-  // TODO(#10678): Handle missing SOF packets
+  // Capture frame number (host sends every 1ms)
+  // Generate an internal SOF if the host's is missing.
+  logic [10:0] frame_d, frame_q;
+
+  assign frame_o = frame_q;
+  assign frame_start_o = (frame_q != frame_d);
+
+  always_comb begin
+    frame_d = frame_q;
+    if (sof_valid_o) begin
+      frame_d = frame_index_raw;
+    end else if (do_internal_sof) begin
+      frame_d = frame_q + 1;
+    end
+  end
+
   always_ff @(posedge clk_48mhz_i or negedge rst_ni) begin
     if (!rst_ni) begin
-      frame_o <= '0;
+      frame_q <= '0;
     end else begin
-      if (sof_valid) begin
-        frame_o <= frame_index_raw;
-      end
+      frame_q <= frame_d;
     end
   end
 
@@ -373,7 +386,7 @@
     .usb_pullup_en_i       (enable_i),
     .rx_jjj_det_i          (rx_jjj_det),
     .rx_j_det_i            (rx_j_det),
-    .sof_valid_i           (sof_valid),
+    .sof_valid_i           (sof_valid_o),
     .resume_link_active_i  (resume_link_active_i),
     .link_disconnect_o     (link_disconnect_o),
     .link_powered_o        (link_powered_o),
@@ -382,7 +395,8 @@
     .link_suspend_o        (link_suspend_o),
     .link_resume_o         (link_resume_o),
     .link_state_o          (link_state_o),
-    .host_lost_o           (host_lost_o)
+    .host_lost_o           (host_lost_o),
+    .sof_missed_o          (do_internal_sof)
   );
 
   ////////////////