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diff --git a/examples/device/cdc_msc_throughput/src/main.c b/examples/device/cdc_msc_throughput/src/main.c
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+++ b/examples/device/cdc_msc_throughput/src/main.c
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+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Ha Thach (tinyusb.org)
+ *
+ * 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.
+ *
+ */
+
+#include "bsp/board_api.h"
+#include "tusb.h"
+
+// cdc_msc_throughput: minimal CDC+MSC device aimed at measuring pure USB bulk throughput.
+// MSC read/write callbacks don't touch any backing storage - write discards the
+// data and read only zero-fills the low LBAs the host scans during enumeration
+// (partition table, GPT header). Higher LBAs return whatever is already in the
+// transfer buffer, so `dd` numbers reflect the USB/driver ceiling, not any
+// simulated storage or per-byte memset cost.
+// CDC path drains RX in tud_cdc_rx_cb and sources TX from a static filler in the
+// main loop so `dd` can target /dev/ttyACMx in either direction.
+
+static void cdc_throughput_task(void);
+
+//--------------------------------------------------------------------+
+// Main
+//--------------------------------------------------------------------+
+int main(void) {
+  board_init();
+
+  tusb_rhport_init_t dev_init = {.role = TUSB_ROLE_DEVICE, .speed = TUSB_SPEED_AUTO};
+  tusb_init(BOARD_TUD_RHPORT, &dev_init);
+
+  board_init_after_tusb();
+
+  while (1) {
+    tud_task();
+    cdc_throughput_task();
+  }
+}
+
+//--------------------------------------------------------------------+
+// CDC callbacks + tasks
+//--------------------------------------------------------------------+
+void tud_cdc_rx_cb(uint8_t itf) {
+  (void) itf;
+  tud_cdc_read_flush(); // Drain RX
+}
+
+static void cdc_throughput_task(void) {
+  if (!tud_cdc_connected()) return;
+
+  // Source TX: fill whatever write room is free.
+  static uint8_t const filler[CFG_TUD_CDC_TX_EPSIZE] = {0};
+  uint32_t room = tud_cdc_write_available();
+  while (room > 0) {
+    uint32_t n = tud_cdc_write(filler, tu_min32(room, sizeof(filler)));
+    if (n == 0) {
+      break;
+    }
+    room -= n;
+  }
+  tud_cdc_write_flush();
+}
+
+//--------------------------------------------------------------------+
+// MSC callbacks
+//--------------------------------------------------------------------+
+
+// 1 GiB logical capacity so `dd` can run long enough for stable numbers.
+// No real backing store - block content is synthesised on read, discarded on write.
+enum {
+  DISK_BLOCK_SIZE  = 512,
+  DISK_BLOCK_COUNT = 0x00200000u, // 2 Mi blocks = 1 GiB
+  // Kernel probes partition-table / filesystem-superblock locations near the
+  // start of the disk during enumeration. Zero-fill only this head range so the
+  // block layer sees "no partition, no filesystem" and leaves us alone; higher
+  // LBAs skip the memset so `dd` measures pure USB/driver throughput.
+  DISK_ZEROFILL_LBA = 64, // 32 KiB
+};
+
+void tud_msc_inquiry_cb(uint8_t lun, uint8_t vendor_id[8], uint8_t product_id[16], uint8_t product_rev[4]) {
+  (void) lun;
+  const char vid[] = "TinyUSB";
+  const char pid[] = "Mass Storage";
+  const char rev[] = "1.0";
+  (void) strncpy((char*) vendor_id, vid, 8);
+  (void) strncpy((char*) product_id, pid, 16);
+  (void) strncpy((char*) product_rev, rev, 4);
+}
+
+bool tud_msc_test_unit_ready_cb(uint8_t lun) {
+  (void) lun;
+  return true;
+}
+
+void tud_msc_capacity_cb(uint8_t lun, uint32_t *block_count, uint16_t *block_size) {
+  (void) lun;
+  *block_count = DISK_BLOCK_COUNT;
+  *block_size  = DISK_BLOCK_SIZE;
+}
+
+bool tud_msc_start_stop_cb(uint8_t lun, uint8_t power_condition, bool start, bool load_eject) {
+  (void) lun; (void) power_condition; (void) start; (void) load_eject;
+  return true;
+}
+
+bool tud_msc_is_writable_cb(uint8_t lun) {
+  (void) lun;
+  return true;
+}
+
+// READ10: zero-fill only the head range the kernel inspects, skip memset everywhere
+// else so we measure the USB / driver path rather than memset cost.
+int32_t tud_msc_read10_cb(uint8_t lun, uint32_t lba, uint32_t offset, void *buffer, uint32_t bufsize) {
+  (void) lun; (void) offset;
+  if (lba < DISK_ZEROFILL_LBA) {
+    memset(buffer, 0, bufsize);
+  } else {
+    (void) buffer;
+  }
+  return (int32_t) bufsize;
+}
+
+// WRITE10: discard the received data entirely - this is the pure USB-speed test.
+int32_t tud_msc_write10_cb(uint8_t lun, uint32_t lba, uint32_t offset, uint8_t *buffer, uint32_t bufsize) {
+  (void) lun; (void) lba; (void) offset; (void) buffer;
+  return (int32_t) bufsize;
+}
+
+// Unknown SCSI commands: stall with Invalid Command sense.
+int32_t tud_msc_scsi_cb(uint8_t lun, uint8_t const scsi_cmd[16], void *buffer, uint16_t bufsize) {
+  (void) scsi_cmd; (void) buffer; (void) bufsize;
+  tud_msc_set_sense(lun, SCSI_SENSE_ILLEGAL_REQUEST, 0x20, 0x00);
+  return -1;
+}