diff --git a/firmware/include/ring_buffer.h b/firmware/include/ring_buffer.h
index 6070c05..01e820c 100644
--- a/firmware/include/ring_buffer.h
+++ b/firmware/include/ring_buffer.h
@@ -13,15 +13,17 @@ struct ring_buffer {
     uint16_t free() const { return N - used(); }
     bool empty() const { return head == tail; }
 
-    void push(std::span<const T> src) {
-        if (src.size() > free()) return;
+    bool push(std::span<const T> src) {
+        if (src.size() > free()) return false;
         for (auto& v : src)
             data[(tail++) % N] = v;
+        return true;
     }
 
-    void push(const T& v) {
-        if (free() == 0) return;
+    bool push(const T& v) {
+        if (free() == 0) return false;
         data[(tail++) % N] = v;
+        return true;
     }
 
     void push_overwrite(const T& v) {
diff --git a/firmware/include/usb_cdc.h b/firmware/include/usb_cdc.h
index cd82a16..bf75333 100644
--- a/firmware/include/usb_cdc.h
+++ b/firmware/include/usb_cdc.h
@@ -8,9 +8,10 @@
 struct usb_cdc {
     ring_buffer<uint8_t, 8192> tx;
 
-    void send(std::span<const uint8_t> data) {
-        tx.push(data);
+    bool send(std::span<const uint8_t> data) {
+        if (!tx.push(data)) return false;
         drain();
+        return true;
     }
 
     void send(const std::vector<uint8_t>& data) {
diff --git a/firmware/lib/dispatch.cpp b/firmware/lib/dispatch.cpp
index 3a11861..e2a5206 100644
--- a/firmware/lib/dispatch.cpp
+++ b/firmware/lib/dispatch.cpp
@@ -26,7 +26,9 @@ void dispatch_init() {
 }
 
 timer_handle dispatch_schedule_ms(uint32_t ms, std::function<void()> fn) {
-    return timers.schedule_ms(ms, std::move(fn));
+    auto h = timers.schedule_ms(ms, std::move(fn));
+    if (!h) dlogf("timer alloc failed: %lu ms", static_cast<unsigned long>(ms));
+    return h;
 }
 
 bool dispatch_cancel_timer(timer_handle h) {
@@ -45,7 +47,10 @@ bool dispatch_cancel_timer(timer_handle h) {
 
     auto dispatch_msg = [&](const DecodedMessage& msg, std::function<void(std::span<const uint8_t>)> send) {
         auto it = handler_map.find(msg.type_id);
-        if (it == handler_map.end()) return;
+        if (it == handler_map.end()) {
+            dlogf("dispatch: unknown type_id %d", msg.type_id);
+            return;
+        }
         responder resp{msg.message_id, std::move(send)};
         it->second(resp, msg.payload);
     };
@@ -79,8 +84,10 @@ bool dispatch_cancel_timer(timer_handle h) {
 
             dispatch_msg(*msg, [&](std::span<const uint8_t> data) {
                 if (data.size() <= usb.tx.free()) {
-                    usb.send(data);
+                    if (!usb.send(data))
+                        dlogf("usb send failed: %zu bytes, %u free", data.size(), usb.tx.free());
                 } else {
+                    dlogf("usb response too large: %zu bytes, %u free", data.size(), usb.tx.free());
                     uint8_t err_buf[256];
                     span_writer err_out(err_buf, sizeof(err_buf));
                     auto err = encode_response_into(err_out, msg->message_id,
diff --git a/firmware/lib/net.cpp b/firmware/lib/net.cpp
index fa76346..2583c0e 100644
--- a/firmware/lib/net.cpp
+++ b/firmware/lib/net.cpp
@@ -22,7 +22,10 @@ static std::vector<net_frame_callback> frame_callbacks;
 
 void net_send_raw(std::span<const uint8_t> data) {
     dlog_if_slow("net_send_raw", 1000, [&]{
-        w6300::send(raw_socket, data);
+        auto result = w6300::send(raw_socket, data);
+        if (!result)
+            dlogf("w6300 send failed: %zu bytes, err %d",
+                  data.size(), static_cast<int>(result.error()));
     });
 }
 
diff --git a/firmware/lib/test_handlers.cpp b/firmware/lib/test_handlers.cpp
index 01cd67d..625db72 100644
--- a/firmware/lib/test_handlers.cpp
+++ b/firmware/lib/test_handlers.cpp
@@ -254,7 +254,7 @@ static void start_ping_rate(const responder& resp, uint16_t target,
                 ping_rate_send_one(st);
             net_add_frame_callback(*cb);
 
-            st->timer = dispatch_schedule_ms(60000, [st]() {
+            st->timer = dispatch_schedule_ms(10000, [st]() {
                 uint32_t elapsed_us = time_us_32() - st->start_us;
                 char msg[64];
                 snprintf(msg, sizeof(msg), "timeout after %u/%u rt in %lu ms",