Merge pull request #2227 from rgrr/ncm_device_new2

Rewrite of NCM device driver

3 files changed, 849 insertions, 395 deletions

diff --git a/src/class/net/ncm.h b/src/class/net/ncm.h
index 96ba11fbc..1b987fca0 100644
--- a/src/class/net/ncm.h
+++ b/src/class/net/ncm.h
@@ -2,6 +2,7 @@
  * The MIT License (MIT)
  *
  * Copyright (c) 2021, Ha Thach (tinyusb.org)
+ * Copyright (c) 2024, Hardy Griech
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -24,22 +25,58 @@
  * This file is part of the TinyUSB stack.
  */
 
-
 #ifndef _TUSB_NCM_H_
 #define _TUSB_NCM_H_
 
 #include "common/tusb_common.h"
 
-#ifdef __cplusplus
- extern "C" {
+// NTB buffers size for reception side, must be >> MTU to avoid TCP retransmission (driver issue ?)
+// Linux use 2048 as minimal size
+#ifndef CFG_TUD_NCM_OUT_NTB_MAX_SIZE
+  #define CFG_TUD_NCM_OUT_NTB_MAX_SIZE 3200
 #endif
 
-// Table 4.3 Data Class Interface Protocol Codes
-typedef enum
-{
-  NCM_DATA_PROTOCOL_NETWORK_TRANSFER_BLOCK = 0x01
-} ncm_data_interface_protocol_code_t;
+// NTB buffers size for reception side, must be > MTU
+// Linux use 2048 as minimal size
+#ifndef CFG_TUD_NCM_IN_NTB_MAX_SIZE
+  #define CFG_TUD_NCM_IN_NTB_MAX_SIZE 3200
+#endif
+
+// Number of NTB buffers for reception side
+// Depending on the configuration, this parameter could be increased with the cost of additional RAM requirements
+// On Full-Speed (RP2040) :
+//    1  - good performance
+//    2  - up to 30% more performance with iperf with small packets
+//    >2 - no performance gain
+// On High-Speed (STM32F7) :
+//    No performance gain
+#ifndef CFG_TUD_NCM_OUT_NTB_N
+  #define CFG_TUD_NCM_OUT_NTB_N 1
+#endif
 
+// Number of NTB buffers for transmission side
+// Depending on the configuration, this parameter could be increased with the cost of additional RAM requirements
+// On Full-Speed (RP2040) :
+//    1 - good performance but SystemView shows lost events (on load test)
+//    2 - up to 50% more performance with iperf with small packets, "tud_network_can_xmit: request blocked"
+//        happens from time to time with SystemView
+//    3 - "tud_network_can_xmit: request blocked" never happens
+//    >3 - no performance gain
+// On High-Speed (STM32F7) :
+//    No performance gain
+#ifndef CFG_TUD_NCM_IN_NTB_N
+  #define CFG_TUD_NCM_IN_NTB_N 1
+#endif
+
+// How many datagrams it is allowed to put into an NTB for transmission side
+#ifndef CFG_TUD_NCM_IN_MAX_DATAGRAMS_PER_NTB
+  #define CFG_TUD_NCM_IN_MAX_DATAGRAMS_PER_NTB 8
+#endif
+
+// This tells the host how many datagrams it is allowed to put into an NTB
+#ifndef CFG_TUD_NCM_OUT_MAX_DATAGRAMS_PER_NTB
+  #define CFG_TUD_NCM_OUT_MAX_DATAGRAMS_PER_NTB 6
+#endif
 
 // Table 6.2 Class-Specific Request Codes for Network Control Model subclass
 typedef enum
@@ -62,8 +99,65 @@ typedef enum
   NCM_SET_CRC_MODE                                 = 0x8A,
 } ncm_request_code_t;
 
-#ifdef __cplusplus
- }
-#endif
+#define NTH16_SIGNATURE 0x484D434E
+#define NDP16_SIGNATURE_NCM0 0x304D434E
+#define NDP16_SIGNATURE_NCM1 0x314D434E
+
+typedef struct TU_ATTR_PACKED {
+  uint16_t wLength;
+  uint16_t bmNtbFormatsSupported;
+  uint32_t dwNtbInMaxSize;
+  uint16_t wNdbInDivisor;
+  uint16_t wNdbInPayloadRemainder;
+  uint16_t wNdbInAlignment;
+  uint16_t wReserved;
+  uint32_t dwNtbOutMaxSize;
+  uint16_t wNdbOutDivisor;
+  uint16_t wNdbOutPayloadRemainder;
+  uint16_t wNdbOutAlignment;
+  uint16_t wNtbOutMaxDatagrams;
+} ntb_parameters_t;
+
+typedef struct TU_ATTR_PACKED {
+  uint32_t dwSignature;
+  uint16_t wHeaderLength;
+  uint16_t wSequence;
+  uint16_t wBlockLength;
+  uint16_t wNdpIndex;
+} nth16_t;
+
+typedef struct TU_ATTR_PACKED {
+  uint16_t wDatagramIndex;
+  uint16_t wDatagramLength;
+} ndp16_datagram_t;
+
+typedef struct TU_ATTR_PACKED {
+  uint32_t dwSignature;
+  uint16_t wLength;
+  uint16_t wNextNdpIndex;
+  //ndp16_datagram_t datagram[];
+} ndp16_t;
+
+typedef union TU_ATTR_PACKED {
+  struct {
+    nth16_t nth;
+    ndp16_t ndp;
+    ndp16_datagram_t ndp_datagram[CFG_TUD_NCM_IN_MAX_DATAGRAMS_PER_NTB + 1];
+  };
+  uint8_t data[CFG_TUD_NCM_IN_NTB_MAX_SIZE];
+} xmit_ntb_t;
+
+typedef union TU_ATTR_PACKED {
+  struct {
+    nth16_t nth;
+    // only the header is at a guaranteed position
+  };
+  uint8_t data[CFG_TUD_NCM_OUT_NTB_MAX_SIZE];
+} recv_ntb_t;
+
+struct ncm_notify_t {
+  tusb_control_request_t header;
+  uint32_t downlink, uplink;
+};
 
 #endif
diff --git a/src/class/net/ncm_device.c b/src/class/net/ncm_device.c
index f84bd9f73..4b237e4cf 100644
--- a/src/class/net/ncm_device.c
+++ b/src/class/net/ncm_device.c
@@ -1,9 +1,8 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2020 Jacob Berg Potter
- * Copyright (c) 2020 Peter Lawrence
  * Copyright (c) 2019 Ha Thach (tinyusb.org)
+ * Copyright (c) 2024 Hardy Griech
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -26,12 +25,37 @@
  * This file is part of the TinyUSB stack.
  */
 
+/**
+ * Small Glossary (from the spec)
+ * --------------
+ * Datagram - A collection of bytes forming a single item of information, passed as a unit from source to destination.
+ * NCM      - Network Control Model
+ * NDP      - NCM Datagram Pointer: NTB structure that delineates Datagrams (typically Ethernet frames) within an NTB
+ * NTB      - NCM Transfer Block: a data structure for efficient USB encapsulation of one or more datagrams
+ *            Each NTB is designed to be a single USB transfer
+ * NTH      - NTB Header: a data structure at the front of each NTB, which provides the information needed to validate
+ *            the NTB and begin decoding
+ *
+ * Some explanations
+ * -----------------
+ * - rhport        is the USB port of the device, in most cases "0"
+ * - itf_data_alt  if != 0 -> data xmit/recv are allowed (see spec)
+ * - ep_in         IN endpoints take data from the device intended to go in to the host (the device transmits)
+ * - ep_out        OUT endpoints send data out of the host to the device (the device receives)
+ */
+
 #include "tusb_option.h"
 
-#if ( CFG_TUD_ENABLED && CFG_TUD_NCM )
+#if (CFG_TUD_ENABLED && CFG_TUD_NCM)
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
 
 #include "device/usbd.h"
 #include "device/usbd_pvt.h"
+
+#include "ncm.h"
 #include "net_device.h"
 
 // Level where CFG_TUSB_DEBUG must be at least for this driver is logged
@@ -41,482 +65,829 @@
 
 #define TU_LOG_DRV(...)   TU_LOG(CFG_TUD_NCM_LOG_LEVEL, __VA_ARGS__)
 
-//--------------------------------------------------------------------+
-// MACRO CONSTANT TYPEDEF
-//--------------------------------------------------------------------+
+// Alignment must be 4
+#define TUD_NCM_ALIGNMENT   4
+// calculate alignment of xmit datagrams within an NTB
+#define XMIT_ALIGN_OFFSET(x) ((TUD_NCM_ALIGNMENT - ((x) & (TUD_NCM_ALIGNMENT - 1))) & (TUD_NCM_ALIGNMENT - 1))
 
-#define NTH16_SIGNATURE      0x484D434E
-#define NDP16_SIGNATURE_NCM0 0x304D434E
-#define NDP16_SIGNATURE_NCM1 0x314D434E
+//-----------------------------------------------------------------------------
+//
+// Module global things
+//
+#define XMIT_NTB_N CFG_TUD_NCM_IN_NTB_N
+#define RECV_NTB_N CFG_TUD_NCM_OUT_NTB_N
 
-typedef struct TU_ATTR_PACKED
-{
-  uint16_t wLength;
-  uint16_t bmNtbFormatsSupported;
-  uint32_t dwNtbInMaxSize;
-  uint16_t wNdbInDivisor;
-  uint16_t wNdbInPayloadRemainder;
-  uint16_t wNdbInAlignment;
-  uint16_t wReserved;
-  uint32_t dwNtbOutMaxSize;
-  uint16_t wNdbOutDivisor;
-  uint16_t wNdbOutPayloadRemainder;
-  uint16_t wNdbOutAlignment;
-  uint16_t wNtbOutMaxDatagrams;
-} ntb_parameters_t;
+typedef struct {
+  // general
+  uint8_t ep_in;        // endpoint for outgoing datagrams (naming is a little bit confusing)
+  uint8_t ep_out;       // endpoint for incoming datagrams (naming is a little bit confusing)
+  uint8_t ep_notif;     // endpoint for notifications
+  uint8_t itf_num;      // interface number
+  uint8_t itf_data_alt; // ==0 -> no endpoints, i.e. no network traffic, ==1 -> normal operation with two endpoints (spec, chapter 5.3)
+  uint8_t rhport;       // storage of \a rhport because some callbacks are done without it
 
-typedef struct TU_ATTR_PACKED
-{
-  uint32_t dwSignature;
-  uint16_t wHeaderLength;
-  uint16_t wSequence;
-  uint16_t wBlockLength;
-  uint16_t wNdpIndex;
-} nth16_t;
+  // recv handling
+  CFG_TUSB_MEM_ALIGN recv_ntb_t recv_ntb[RECV_NTB_N];   // actual recv NTBs
+  recv_ntb_t *recv_free_ntb[RECV_NTB_N];                // free list of recv NTBs
+  recv_ntb_t *recv_ready_ntb[RECV_NTB_N];               // NTBs waiting for transmission to glue logic
+  recv_ntb_t *recv_tinyusb_ntb;                         // buffer for the running transfer TinyUSB -> driver
+  recv_ntb_t *recv_glue_ntb;                            // buffer for the running transfer driver -> glue logic
+  uint16_t recv_glue_ntb_datagram_ndx;                  // index into \a recv_glue_ntb_datagram
 
-typedef struct TU_ATTR_PACKED
-{
-  uint16_t wDatagramIndex;
-  uint16_t wDatagramLength;
-} ndp16_datagram_t;
+  // xmit handling
+  CFG_TUSB_MEM_ALIGN xmit_ntb_t xmit_ntb[XMIT_NTB_N];   // actual xmit NTBs
+  xmit_ntb_t *xmit_free_ntb[XMIT_NTB_N];                // free list of xmit NTBs
+  xmit_ntb_t *xmit_ready_ntb[XMIT_NTB_N];               // NTBs waiting for transmission to TinyUSB
+  xmit_ntb_t *xmit_tinyusb_ntb;                         // buffer for the running transfer driver -> TinyUSB
+  xmit_ntb_t *xmit_glue_ntb;                            // buffer for the running transfer glue logic -> driver
+  uint16_t xmit_sequence;                               // NTB sequence counter
+  uint16_t xmit_glue_ntb_datagram_ndx;                  // index into \a xmit_glue_ntb_datagram
 
-typedef struct TU_ATTR_PACKED
-{
-  uint32_t dwSignature;
-  uint16_t wLength;
-  uint16_t wNextNdpIndex;
-  ndp16_datagram_t datagram[];
-} ndp16_t;
+  // notification handling
+  enum {
+    NOTIFICATION_SPEED,
+    NOTIFICATION_CONNECTED,
+    NOTIFICATION_DONE
+  } notification_xmit_state;            // state of notification transmission
+  bool notification_xmit_is_running;    // notification is currently transmitted
+} ncm_interface_t;
 
-typedef union TU_ATTR_PACKED {
-  struct {
-    nth16_t nth;
-    ndp16_t ndp;
-  };
-  uint8_t data[CFG_TUD_NCM_IN_NTB_MAX_SIZE];
-} transmit_ntb_t;
+CFG_TUSB_MEM_SECTION CFG_TUSB_MEM_ALIGN tu_static ncm_interface_t ncm_interface;
 
-struct ecm_notify_struct
-{
-  tusb_control_request_t header;
-  uint32_t downlink, uplink;
+/**
+ * This is the NTB parameter structure
+ *
+ * \attention
+ *     We are lucky, that byte order is correct
+ */
+CFG_TUSB_MEM_SECTION CFG_TUSB_MEM_ALIGN tu_static const ntb_parameters_t ntb_parameters = {
+  .wLength                  = sizeof(ntb_parameters_t),
+  .bmNtbFormatsSupported    = 0x01,// 16-bit NTB supported
+  .dwNtbInMaxSize           = CFG_TUD_NCM_IN_NTB_MAX_SIZE,
+  .wNdbInDivisor            = 1,
+  .wNdbInPayloadRemainder   = 0,
+  .wNdbInAlignment          = TUD_NCM_ALIGNMENT,
+  .wReserved                = 0,
+  .dwNtbOutMaxSize          = CFG_TUD_NCM_OUT_NTB_MAX_SIZE,
+  .wNdbOutDivisor           = 1,
+  .wNdbOutPayloadRemainder  = 0,
+  .wNdbOutAlignment         = TUD_NCM_ALIGNMENT,
+  .wNtbOutMaxDatagrams      = CFG_TUD_NCM_OUT_MAX_DATAGRAMS_PER_NTB,
 };
 
-typedef struct
-{
-  uint8_t itf_num;      // Index number of Management Interface, +1 for Data Interface
-  uint8_t itf_data_alt; // Alternate setting of Data Interface. 0 : inactive, 1 : active
+// Some confusing remarks about wNtbOutMaxDatagrams...
+//      ==1 -> SystemView packets/s goes up to 2000 and events are lost during startup
+//      ==0 -> SystemView runs fine, iperf shows in wireshark a lot of error
+//      ==6 -> SystemView runs fine, iperf also
+//      >6  -> iperf starts to show errors
+//      -> 6 seems to be the best value.  Why?  Don't know, perhaps only on my system?
+//
+//      iperf:    for MSS in 100 200 400 800 1200 1450 1500; do iperf -c 192.168.14.1 -e -i 1 -M $MSS -l 8192 -P 1; sleep 2; done
+//      sysview:  SYSTICKS_PER_SEC=35000, IDLE_US=1000, PRINT_MOD=1000
+//
 
-  uint8_t ep_notif;
-  uint8_t ep_in;
-  uint8_t ep_out;
+//-----------------------------------------------------------------------------
+//
+// everything about notifications
+//
+tu_static struct ncm_notify_t ncm_notify_connected = {
+    .header = {
+        .bmRequestType_bit = {
+            .recipient = TUSB_REQ_RCPT_INTERFACE,
+            .type = TUSB_REQ_TYPE_CLASS,
+            .direction = TUSB_DIR_IN},
+        .bRequest = CDC_NOTIF_NETWORK_CONNECTION,
+        .wValue = 1 /* Connected */,
+        .wLength = 0,
+    },
+};
 
-  const ndp16_t *ndp;
-  uint8_t num_datagrams, current_datagram_index;
+tu_static struct ncm_notify_t ncm_notify_speed_change = {
+    .header = {
+        .bmRequestType_bit = {
+            .recipient = TUSB_REQ_RCPT_INTERFACE,
+            .type = TUSB_REQ_TYPE_CLASS,
+            .direction = TUSB_DIR_IN},
+        .bRequest = CDC_NOTIF_CONNECTION_SPEED_CHANGE,
+        .wLength = 8,
+    },
+    .downlink = TUD_OPT_HIGH_SPEED ? 480000000 : 12000000,
+    .uplink = TUD_OPT_HIGH_SPEED ? 480000000 : 12000000,
+};
 
-  enum {
-    REPORT_SPEED,
-    REPORT_CONNECTED,
-    REPORT_DONE
-  } report_state;
-  bool report_pending;
+/**
+ * Transmit next notification to the host (if appropriate).
+ * Notifications are transferred to the host once during connection setup.
+ */
+static void notification_xmit(uint8_t rhport, bool force_next) {
+  TU_LOG_DRV("notification_xmit(%d, %d) - %d %d\n", force_next, rhport, ncm_interface.notification_xmit_state, ncm_interface.notification_xmit_is_running);
 
-  uint8_t  current_ntb;           // Index in transmit_ntb[] that is currently being filled with datagrams
-  uint8_t  datagram_count;        // Number of datagrams in transmit_ntb[current_ntb]
-  uint16_t next_datagram_offset;  // Offset in transmit_ntb[current_ntb].data to place the next datagram
-  uint16_t ntb_in_size;           // Maximum size of transmitted (IN to host) NTBs; initially CFG_TUD_NCM_IN_NTB_MAX_SIZE
-  uint8_t  max_datagrams_per_ntb; // Maximum number of datagrams per NTB; initially CFG_TUD_NCM_MAX_DATAGRAMS_PER_NTB
+  if (!force_next && ncm_interface.notification_xmit_is_running) {
+    return;
+  }
 
-  uint16_t nth_sequence;          // Sequence number counter for transmitted NTBs
+  if (ncm_interface.notification_xmit_state == NOTIFICATION_SPEED) {
+    TU_LOG_DRV("  NOTIFICATION_SPEED\n");
+    ncm_notify_speed_change.header.wIndex = ncm_interface.itf_num;
+    usbd_edpt_xfer(rhport, ncm_interface.ep_notif, (uint8_t *) &ncm_notify_speed_change, sizeof(ncm_notify_speed_change));
+    ncm_interface.notification_xmit_state = NOTIFICATION_CONNECTED;
+    ncm_interface.notification_xmit_is_running = true;
+  } else if (ncm_interface.notification_xmit_state == NOTIFICATION_CONNECTED) {
+    TU_LOG_DRV("  NOTIFICATION_CONNECTED\n");
+    ncm_notify_connected.header.wIndex = ncm_interface.itf_num;
+    usbd_edpt_xfer(rhport, ncm_interface.ep_notif, (uint8_t *) &ncm_notify_connected, sizeof(ncm_notify_connected));
+    ncm_interface.notification_xmit_state = NOTIFICATION_DONE;
+    ncm_interface.notification_xmit_is_running = true;
+  } else {
+    TU_LOG_DRV("  NOTIFICATION_FINISHED\n");
+  }
+} // notification_xmit
 
-  bool transferring;
+//-----------------------------------------------------------------------------
+//
+// everything about packet transmission (driver -> TinyUSB)
+//
 
-} ncm_interface_t;
+/**
+ * Put NTB into the transmitter free list.
+ */
+static void xmit_put_ntb_into_free_list(xmit_ntb_t *free_ntb) {
+  TU_LOG_DRV("xmit_put_ntb_into_free_list() - %p\n", ncm_interface.xmit_tinyusb_ntb);
 
-//--------------------------------------------------------------------+
-// INTERNAL OBJECT & FUNCTION DECLARATION
-//--------------------------------------------------------------------+
+  if (free_ntb == NULL) { // can happen due to ZLPs
+    return;
+  }
 
-CFG_TUD_MEM_SECTION CFG_TUSB_MEM_ALIGN tu_static const ntb_parameters_t ntb_parameters = {
-    .wLength                 = sizeof(ntb_parameters_t),
-    .bmNtbFormatsSupported   = 0x01,
-    .dwNtbInMaxSize          = CFG_TUD_NCM_IN_NTB_MAX_SIZE,
-    .wNdbInDivisor           = 4,
-    .wNdbInPayloadRemainder  = 0,
-    .wNdbInAlignment         = CFG_TUD_NCM_ALIGNMENT,
-    .wReserved               = 0,
-    .dwNtbOutMaxSize         = CFG_TUD_NCM_OUT_NTB_MAX_SIZE,
-    .wNdbOutDivisor          = 4,
-    .wNdbOutPayloadRemainder = 0,
-    .wNdbOutAlignment        = CFG_TUD_NCM_ALIGNMENT,
-    .wNtbOutMaxDatagrams     = 0
-};
+  for (int i = 0; i < XMIT_NTB_N; ++i) {
+    if (ncm_interface.xmit_free_ntb[i] == NULL) {
+      ncm_interface.xmit_free_ntb[i] = free_ntb;
+      return;
+    }
+  }
+  TU_LOG_DRV("(EE) xmit_put_ntb_into_free_list - no entry in free list\n");// this should not happen
+} // xmit_put_ntb_into_free_list
 
-CFG_TUD_MEM_SECTION CFG_TUSB_MEM_ALIGN tu_static transmit_ntb_t transmit_ntb[2];
+/**
+ * Get an NTB from the free list
+ */
+static xmit_ntb_t *xmit_get_free_ntb(void) {
+  TU_LOG_DRV("xmit_get_free_ntb()\n");
 
-CFG_TUD_MEM_SECTION CFG_TUSB_MEM_ALIGN tu_static uint8_t receive_ntb[CFG_TUD_NCM_OUT_NTB_MAX_SIZE];
+  for (int i = 0; i < XMIT_NTB_N; ++i) {
+    if (ncm_interface.xmit_free_ntb[i] != NULL) {
+      xmit_ntb_t *free = ncm_interface.xmit_free_ntb[i];
+      ncm_interface.xmit_free_ntb[i] = NULL;
+      return free;
+    }
+  }
+  return NULL;
+} // xmit_get_free_ntb
 
-tu_static ncm_interface_t ncm_interface;
+/**
+ * Put a filled NTB into the ready list
+ */
+static void xmit_put_ntb_into_ready_list(xmit_ntb_t *ready_ntb) {
+  TU_LOG_DRV("xmit_put_ntb_into_ready_list(%p) %d\n", ready_ntb, ready_ntb->nth.wBlockLength);
 
-/*
- * Set up the NTB state in ncm_interface to be ready to add datagrams.
+  for (int i = 0; i < XMIT_NTB_N; ++i) {
+    if (ncm_interface.xmit_ready_ntb[i] == NULL) {
+      ncm_interface.xmit_ready_ntb[i] = ready_ntb;
+      return;
+    }
+  }
+  TU_LOG_DRV("(EE) xmit_put_ntb_into_ready_list: ready list full\n");// this should not happen
+} // xmit_put_ntb_into_ready_list
+
+/**
+ * Get the next NTB from the ready list (and remove it from the list).
+ * If the ready list is empty, return NULL.
  */
-static void ncm_prepare_for_tx(void) {
-  ncm_interface.datagram_count = 0;
-  // datagrams start after all the headers
-  ncm_interface.next_datagram_offset = sizeof(nth16_t) + sizeof(ndp16_t)
-      + ((CFG_TUD_NCM_MAX_DATAGRAMS_PER_NTB + 1) * sizeof(ndp16_datagram_t));
-}
+static xmit_ntb_t *xmit_get_next_ready_ntb(void) {
+  xmit_ntb_t *r = NULL;
 
-/*
- * If not already transmitting, start sending the current NTB to the host and swap buffers
- * to start filling the other one with datagrams.
+  r = ncm_interface.xmit_ready_ntb[0];
+  memmove(ncm_interface.xmit_ready_ntb + 0, ncm_interface.xmit_ready_ntb + 1, sizeof(ncm_interface.xmit_ready_ntb) - sizeof(ncm_interface.xmit_ready_ntb[0]));
+  ncm_interface.xmit_ready_ntb[XMIT_NTB_N - 1] = NULL;
+
+  TU_LOG_DRV("recv_get_next_ready_ntb: %p\n", r);
+  return r;
+} // xmit_get_next_ready_ntb
+
+/**
+ * Transmit a ZLP if required
+ *
+ * \note
+ *    Insertion of the ZLPs is a little bit different then described in the spec.
+ *    But the below implementation actually works.  Don't know if this is a spec
+ *    or TinyUSB issue.
+ *
+ * \pre
+ *    This must be called from netd_xfer_cb() so that ep_in is ready
  */
-static void ncm_start_tx(void) {
-  if (ncm_interface.transferring) {
+static bool xmit_insert_required_zlp(uint8_t rhport, uint32_t xferred_bytes) {
+  TU_LOG_DRV("xmit_insert_required_zlp(%d,%d)\n", rhport, xferred_bytes);
+
+  if (xferred_bytes == 0 || xferred_bytes % CFG_TUD_NET_ENDPOINT_SIZE != 0) {
+    return false;
+  }
+
+  TU_ASSERT(ncm_interface.itf_data_alt == 1, false);
+  TU_ASSERT(!usbd_edpt_busy(rhport, ncm_interface.ep_in), false);
+
+  TU_LOG_DRV("xmit_insert_required_zlp! (%u)\n", (unsigned) xferred_bytes);
+
+  // start transmission of the ZLP
+  usbd_edpt_xfer(rhport, ncm_interface.ep_in, NULL, 0);
+
+  return true;
+} // xmit_insert_required_zlp
+
+/**
+ * Start transmission if it there is a waiting packet and if can be done from interface side.
+ */
+static void xmit_start_if_possible(uint8_t rhport) {
+  TU_LOG_DRV("xmit_start_if_possible()\n");
+
+  if (ncm_interface.xmit_tinyusb_ntb != NULL) {
+    TU_LOG_DRV("  !xmit_start_if_possible 1\n");
+    return;
+  }
+  if (ncm_interface.itf_data_alt != 1) {
+    TU_LOG_DRV("(EE) !xmit_start_if_possible 2\n");
     return;
   }
+  if (usbd_edpt_busy(rhport, ncm_interface.ep_in)) {
+    TU_LOG_DRV("  !xmit_start_if_possible 3\n");
+    return;
+  }
+
+  ncm_interface.xmit_tinyusb_ntb = xmit_get_next_ready_ntb();
+  if (ncm_interface.xmit_tinyusb_ntb == NULL) {
+    if (ncm_interface.xmit_glue_ntb == NULL || ncm_interface.xmit_glue_ntb_datagram_ndx == 0) {
+      // -> really nothing is waiting
+      return;
+    }
+    ncm_interface.xmit_tinyusb_ntb = ncm_interface.xmit_glue_ntb;
+    ncm_interface.xmit_glue_ntb = NULL;
+  }
 
-  transmit_ntb_t *ntb = &transmit_ntb[ncm_interface.current_ntb];
-  size_t ntb_length = ncm_interface.next_datagram_offset;
+  #if CFG_TUD_NCM_LOG_LEVEL >= 3
+  {
+    uint16_t len = ncm_interface.xmit_tinyusb_ntb->nth.wBlockLength;
+    TU_LOG_BUF(3, ncm_interface.xmit_tinyusb_ntb->data[i], len);
+  }
+  #endif
+
+  if (ncm_interface.xmit_glue_ntb_datagram_ndx != 1) {
+    TU_LOG_DRV(">> %d %d\n", ncm_interface.xmit_tinyusb_ntb->nth.wBlockLength, ncm_interface.xmit_glue_ntb_datagram_ndx);
+  }
+
+  // Kick off an endpoint transfer
+  usbd_edpt_xfer(0, ncm_interface.ep_in, ncm_interface.xmit_tinyusb_ntb->data, ncm_interface.xmit_tinyusb_ntb->nth.wBlockLength);
+} // xmit_start_if_possible
+
+/**
+ * check if a new datagram fits into the current NTB
+ */
+static bool xmit_requested_datagram_fits_into_current_ntb(uint16_t datagram_size) {
+  TU_LOG_DRV("xmit_requested_datagram_fits_into_current_ntb(%d) - %p %p\n", datagram_size, ncm_interface.xmit_tinyusb_ntb, ncm_interface.xmit_glue_ntb);
+
+  if (ncm_interface.xmit_glue_ntb == NULL) {
+    return false;
+  }
+  if (ncm_interface.xmit_glue_ntb_datagram_ndx >= CFG_TUD_NCM_IN_MAX_DATAGRAMS_PER_NTB) {
+    return false;
+  }
+  if (ncm_interface.xmit_glue_ntb->nth.wBlockLength + datagram_size + XMIT_ALIGN_OFFSET(datagram_size) > CFG_TUD_NCM_OUT_NTB_MAX_SIZE) {
+    return false;
+  }
+  return true;
+} // xmit_requested_datagram_fits_into_current_ntb
+
+/**
+ * Setup an NTB for the glue logic
+ */
+static bool xmit_setup_next_glue_ntb(void) {
+  TU_LOG_DRV("xmit_setup_next_glue_ntb - %p\n", ncm_interface.xmit_glue_ntb);
+
+  if (ncm_interface.xmit_glue_ntb != NULL) {
+    // put NTB into waiting list (the new datagram did not fit in)
+    xmit_put_ntb_into_ready_list(ncm_interface.xmit_glue_ntb);
+  }
+
+  ncm_interface.xmit_glue_ntb = xmit_get_free_ntb();// get next buffer (if any)
+  if (ncm_interface.xmit_glue_ntb == NULL) {
+    TU_LOG_DRV("  xmit_setup_next_glue_ntb - nothing free\n");// should happen rarely
+    return false;
+  }
+
+  ncm_interface.xmit_glue_ntb_datagram_ndx = 0;
+
+  xmit_ntb_t *ntb = ncm_interface.xmit_glue_ntb;
 
   // Fill in NTB header
   ntb->nth.dwSignature = NTH16_SIGNATURE;
-  ntb->nth.wHeaderLength = sizeof(nth16_t);
-  ntb->nth.wSequence = ncm_interface.nth_sequence++;
-  ntb->nth.wBlockLength = ntb_length;
-  ntb->nth.wNdpIndex = sizeof(nth16_t);
+  ntb->nth.wHeaderLength = sizeof(ntb->nth);
+  ntb->nth.wSequence = ncm_interface.xmit_sequence++;
+  ntb->nth.wBlockLength = sizeof(ntb->nth) + sizeof(ntb->ndp) + sizeof(ntb->ndp_datagram);
+  ntb->nth.wNdpIndex = sizeof(ntb->nth);
 
   // Fill in NDP16 header and terminator
   ntb->ndp.dwSignature = NDP16_SIGNATURE_NCM0;
-  ntb->ndp.wLength = sizeof(ndp16_t) + (ncm_interface.datagram_count + 1) * sizeof(ndp16_datagram_t);
+  ntb->ndp.wLength = sizeof(ntb->ndp) + sizeof(ntb->ndp_datagram);
   ntb->ndp.wNextNdpIndex = 0;
-  ntb->ndp.datagram[ncm_interface.datagram_count].wDatagramIndex = 0;
-  ntb->ndp.datagram[ncm_interface.datagram_count].wDatagramLength = 0;
-
-  // Kick off an endpoint transfer
-  usbd_edpt_xfer(0, ncm_interface.ep_in, ntb->data, ntb_length);
-  ncm_interface.transferring = true;
 
-  // Swap to the other NTB and clear it out
-  ncm_interface.current_ntb = 1 - ncm_interface.current_ntb;
-  ncm_prepare_for_tx();
-}
+  memset(ntb->ndp_datagram, 0, sizeof(ntb->ndp_datagram));
+  return true;
+} // xmit_setup_next_glue_ntb
 
-tu_static struct ecm_notify_struct ncm_notify_connected =
-{
-    .header = {
-        .bmRequestType_bit = {
-          .recipient = TUSB_REQ_RCPT_INTERFACE,
-          .type      = TUSB_REQ_TYPE_CLASS,
-          .direction = TUSB_DIR_IN
-        },
-        .bRequest      = CDC_NOTIF_NETWORK_CONNECTION,
-        .wValue        = 1 /* Connected */,
-        .wLength       = 0,
-    },
-};
+//-----------------------------------------------------------------------------
+//
+// all the recv_*() stuff (TinyUSB -> driver -> glue logic)
+//
 
-tu_static struct ecm_notify_struct ncm_notify_speed_change =
-{
-    .header = {
-        .bmRequestType_bit = {
-          .recipient = TUSB_REQ_RCPT_INTERFACE,
-          .type      = TUSB_REQ_TYPE_CLASS,
-          .direction = TUSB_DIR_IN
-        },
-        .bRequest = CDC_NOTIF_CONNECTION_SPEED_CHANGE,
-        .wLength = 8,
-    },
-    .downlink = 10000000,
-    .uplink = 10000000,
-};
+/**
+ * Return pointer to an available receive buffer or NULL.
+ * Returned buffer (if any) has the size \a CFG_TUD_NCM_OUT_NTB_MAX_SIZE.
+ */
+static recv_ntb_t *recv_get_free_ntb(void) {
+  TU_LOG_DRV("recv_get_free_ntb()\n");
 
-void tud_network_recv_renew(void)
-{
-  if (!ncm_interface.num_datagrams)
-  {
-    usbd_edpt_xfer(0, ncm_interface.ep_out, receive_ntb, sizeof(receive_ntb));
-    return;
+  for (int i = 0; i < RECV_NTB_N; ++i) {
+    if (ncm_interface.recv_free_ntb[i] != NULL) {
+      recv_ntb_t *free = ncm_interface.recv_free_ntb[i];
+      ncm_interface.recv_free_ntb[i] = NULL;
+      return free;
+    }
   }
+  return NULL;
+} // recv_get_free_ntb
 
-  const ndp16_t *ndp = ncm_interface.ndp;
-  const int i = ncm_interface.current_datagram_index;
-  ncm_interface.current_datagram_index++;
-  ncm_interface.num_datagrams--;
+/**
+ * Get the next NTB from the ready list (and remove it from the list).
+ * If the ready list is empty, return NULL.
+ */
+static recv_ntb_t *recv_get_next_ready_ntb(void) {
+  recv_ntb_t *r = NULL;
 
-  tud_network_recv_cb(receive_ntb + ndp->datagram[i].wDatagramIndex, ndp->datagram[i].wDatagramLength);
-}
+  r = ncm_interface.recv_ready_ntb[0];
+  memmove(ncm_interface.recv_ready_ntb + 0, ncm_interface.recv_ready_ntb + 1, sizeof(ncm_interface.recv_ready_ntb) - sizeof(ncm_interface.recv_ready_ntb[0]));
+  ncm_interface.recv_ready_ntb[RECV_NTB_N - 1] = NULL;
 
-//--------------------------------------------------------------------+
-// USBD Driver API
-//--------------------------------------------------------------------+
+  TU_LOG_DRV("recv_get_next_ready_ntb: %p\n", r);
+  return r;
+} // recv_get_next_ready_ntb
 
-void netd_init(void)
-{
-  tu_memclr(&ncm_interface, sizeof(ncm_interface));
-  ncm_interface.ntb_in_size = CFG_TUD_NCM_IN_NTB_MAX_SIZE;
-  ncm_interface.max_datagrams_per_ntb = CFG_TUD_NCM_MAX_DATAGRAMS_PER_NTB;
-  ncm_prepare_for_tx();
-}
+/**
+ * Put NTB into the receiver free list.
+ */
+static void recv_put_ntb_into_free_list(recv_ntb_t *free_ntb) {
+  TU_LOG_DRV("recv_put_ntb_into_free_list(%p)\n", free_ntb);
 
-bool netd_deinit(void) {
-  return true;
-}
+  for (int i = 0; i < RECV_NTB_N; ++i) {
+    if (ncm_interface.recv_free_ntb[i] == NULL) {
+      ncm_interface.recv_free_ntb[i] = free_ntb;
+      return;
+    }
+  }
+  TU_LOG_DRV("(EE) recv_put_ntb_into_free_list - no entry in free list\n");// this should not happen
+} // recv_put_ntb_into_free_list
 
-void netd_reset(uint8_t rhport)
-{
-  (void) rhport;
+/**
+ * \a ready_ntb holds a validated NTB,
+ * put this buffer into the waiting list.
+ */
+static void recv_put_ntb_into_ready_list(recv_ntb_t *ready_ntb) {
+  TU_LOG_DRV("recv_put_ntb_into_ready_list(%p) %d\n", ready_ntb, ready_ntb->nth.wBlockLength);
 
-  netd_init();
-}
+  for (int i = 0; i < RECV_NTB_N; ++i) {
+    if (ncm_interface.recv_ready_ntb[i] == NULL) {
+      ncm_interface.recv_ready_ntb[i] = ready_ntb;
+      return;
+    }
+  }
+  TU_LOG_DRV("(EE) recv_put_ntb_into_ready_list: ready list full\n");// this should not happen
+} // recv_put_ntb_into_ready_list
 
-uint16_t netd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t max_len)
-{
-  // confirm interface hasn't already been allocated
-  TU_ASSERT(0 == ncm_interface.ep_notif, 0);
+/**
+ * If possible, start a new reception TinyUSB -> driver.
+ */
+static void recv_try_to_start_new_reception(uint8_t rhport) {
+  TU_LOG_DRV("recv_try_to_start_new_reception(%d)\n", rhport);
 
-  //------------- Management Interface -------------//
-  ncm_interface.itf_num = itf_desc->bInterfaceNumber;
+  if (ncm_interface.itf_data_alt != 1) {
+    return;
+  }
+  if (ncm_interface.recv_tinyusb_ntb != NULL) {
+    return;
+  }
+  if (usbd_edpt_busy(rhport, ncm_interface.ep_out)) {
+    return;
+  }
 
-  uint16_t drv_len = sizeof(tusb_desc_interface_t);
-  uint8_t const * p_desc = tu_desc_next( itf_desc );
+  ncm_interface.recv_tinyusb_ntb = recv_get_free_ntb();
+  if (ncm_interface.recv_tinyusb_ntb == NULL) {
+    return;
+  }
 
-  // Communication Functional Descriptors
-  while ( TUSB_DESC_CS_INTERFACE == tu_desc_type(p_desc) && drv_len <= max_len )
-  {
-    drv_len += tu_desc_len(p_desc);
-    p_desc   = tu_desc_next(p_desc);
+  // initiate transfer
+  TU_LOG_DRV("  start reception\n");
+  bool r = usbd_edpt_xfer(rhport, ncm_interface.ep_out, ncm_interface.recv_tinyusb_ntb->data, CFG_TUD_NCM_OUT_NTB_MAX_SIZE);
+  if (!r) {
+    recv_put_ntb_into_free_list(ncm_interface.recv_tinyusb_ntb);
+    ncm_interface.recv_tinyusb_ntb = NULL;
   }
+} // recv_try_to_start_new_reception
 
-  // notification endpoint (if any)
-  if ( TUSB_DESC_ENDPOINT == tu_desc_type(p_desc) )
-  {
-    TU_ASSERT( usbd_edpt_open(rhport, (tusb_desc_endpoint_t const *) p_desc), 0 );
+/**
+ * Validate incoming datagram.
+ * \return true if valid
+ *
+ * \note
+ *    \a ndp16->wNextNdpIndex != 0 is not supported
+ */
+static bool recv_validate_datagram(const recv_ntb_t *ntb, uint32_t len) {
+  const nth16_t *nth16 = &(ntb->nth);
 
-    ncm_interface.ep_notif = ((tusb_desc_endpoint_t const *) p_desc)->bEndpointAddress;
+  TU_LOG_DRV("recv_validate_datagram(%p, %d)\n", ntb, (int) len);
 
-    drv_len += tu_desc_len(p_desc);
-    p_desc   = tu_desc_next(p_desc);
+  // check header
+  if (nth16->wHeaderLength != sizeof(nth16_t)) {
+    TU_LOG_DRV("(EE) ill nth16 length: %d\n", nth16->wHeaderLength);
+    return false;
+  }
+  if (nth16->dwSignature != NTH16_SIGNATURE) {
+    TU_LOG_DRV("(EE) ill signature: 0x%08x\n", (unsigned) nth16->dwSignature);
+    return false;
+  }
+  if (len < sizeof(nth16_t) + sizeof(ndp16_t) + 2 * sizeof(ndp16_datagram_t)) {
+    TU_LOG_DRV("(EE) ill min len: %d\n", len);
+    return false;
+  }
+  if (nth16->wBlockLength > len) {
+    TU_LOG_DRV("(EE) ill block length: %d > %d\n", nth16->wBlockLength, len);
+    return false;
+  }
+  if (nth16->wBlockLength > CFG_TUD_NCM_OUT_NTB_MAX_SIZE) {
+    TU_LOG_DRV("(EE) ill block length2: %d > %d\n", nth16->wBlockLength, CFG_TUD_NCM_OUT_NTB_MAX_SIZE);
+    return false;
+  }
+  if (nth16->wNdpIndex < sizeof(nth16) || nth16->wNdpIndex > len - (sizeof(ndp16_t) + 2 * sizeof(ndp16_datagram_t))) {
+    TU_LOG_DRV("(EE) ill position of first ndp: %d (%d)\n", nth16->wNdpIndex, len);
+    return false;
   }
 
-  //------------- Data Interface -------------//
-  // - CDC-NCM data interface has 2 alternate settings
-  //   - 0 : zero endpoints for inactive (default)
-  //   - 1 : IN & OUT endpoints for transfer of NTBs
-  TU_ASSERT(TUSB_DESC_INTERFACE == tu_desc_type(p_desc), 0);
+  // check (first) NDP(16)
+  const ndp16_t *ndp16 = (const ndp16_t *) (ntb->data + nth16->wNdpIndex);
 
-  do
-  {
-    tusb_desc_interface_t const * data_itf_desc = (tusb_desc_interface_t const *) p_desc;
-    TU_ASSERT(TUSB_CLASS_CDC_DATA == data_itf_desc->bInterfaceClass, 0);
+  if (ndp16->wLength < sizeof(ndp16_t) + 2 * sizeof(ndp16_datagram_t)) {
+    TU_LOG_DRV("(EE) ill ndp16 length: %d\n", ndp16->wLength);
+    return false;
+  }
+  if (ndp16->dwSignature != NDP16_SIGNATURE_NCM0 && ndp16->dwSignature != NDP16_SIGNATURE_NCM1) {
+    TU_LOG_DRV("(EE) ill signature: 0x%08x\n", (unsigned) ndp16->dwSignature);
+    return false;
+  }
+  if (ndp16->wNextNdpIndex != 0) {
+    TU_LOG_DRV("(EE) cannot handle wNextNdpIndex!=0 (%d)\n", ndp16->wNextNdpIndex);
+    return false;
+  }
 
-    drv_len += tu_desc_len(p_desc);
-    p_desc   = tu_desc_next(p_desc);
-  } while((TUSB_DESC_INTERFACE == tu_desc_type(p_desc)) && (drv_len <= max_len));
+  const ndp16_datagram_t *ndp16_datagram = (const ndp16_datagram_t *) (ntb->data + nth16->wNdpIndex + sizeof(ndp16_t));
+  int ndx = 0;
+  uint16_t max_ndx = (uint16_t) ((ndp16->wLength - sizeof(ndp16_t)) / sizeof(ndp16_datagram_t));
 
-  // Pair of endpoints
-  TU_ASSERT(TUSB_DESC_ENDPOINT == tu_desc_type(p_desc), 0);
+  if (max_ndx > 2) { // number of datagrams in NTB > 1
+    TU_LOG_DRV("<< %d (%d)\n", max_ndx - 1, ntb->nth.wBlockLength);
+  }
+  if (ndp16_datagram[max_ndx - 1].wDatagramIndex != 0 || ndp16_datagram[max_ndx - 1].wDatagramLength != 0) {
+    TU_LOG_DRV("  max_ndx != 0\n");
+    return false;
+  }
+  while (ndp16_datagram[ndx].wDatagramIndex != 0 && ndp16_datagram[ndx].wDatagramLength != 0) {
+    TU_LOG_DRV("  << %d %d\n", ndp16_datagram[ndx].wDatagramIndex, ndp16_datagram[ndx].wDatagramLength);
+    if (ndp16_datagram[ndx].wDatagramIndex > len) {
+      TU_LOG_DRV("(EE) ill start of datagram[%d]: %d (%d)\n", ndx, ndp16_datagram[ndx].wDatagramIndex, len);
+      return false;
+    }
+    if (ndp16_datagram[ndx].wDatagramIndex + ndp16_datagram[ndx].wDatagramLength > len) {
+      TU_LOG_DRV("(EE) ill end of datagram[%d]: %d (%d)\n", ndx, ndp16_datagram[ndx].wDatagramIndex + ndp16_datagram[ndx].wDatagramLength, len);
+      return false;
+    }
+    ++ndx;
+  }
 
-  TU_ASSERT(usbd_open_edpt_pair(rhport, p_desc, 2, TUSB_XFER_BULK, &ncm_interface.ep_out, &ncm_interface.ep_in) );
+  #if CFG_TUD_NCM_LOG_LEVEL >= 3
+  TU_LOG_BUF(3, ntb->data[i], len);
+  #endif
 
-  drv_len += 2*sizeof(tusb_desc_endpoint_t);
+  // -> ntb contains a valid packet structure
+  //    ok... I did not check for garbage within the datagram indices...
+  return true;
+} // recv_validate_datagram
 
-  return drv_len;
-}
+/**
+ * Transfer the next (pending) datagram to the glue logic and return receive buffer if empty.
+ */
+static void recv_transfer_datagram_to_glue_logic(void) {
+  TU_LOG_DRV("recv_transfer_datagram_to_glue_logic()\n");
 
-static void ncm_report(void)
-{
-  uint8_t const rhport = 0;
-  if (ncm_interface.report_state == REPORT_SPEED) {
-    ncm_notify_speed_change.header.wIndex = ncm_interface.itf_num;
-    usbd_edpt_xfer(rhport, ncm_interface.ep_notif, (uint8_t *) &ncm_notify_speed_change, sizeof(ncm_notify_speed_change));
-    ncm_interface.report_state = REPORT_CONNECTED;
-    ncm_interface.report_pending = true;
-  } else if (ncm_interface.report_state == REPORT_CONNECTED) {
-    ncm_notify_connected.header.wIndex = ncm_interface.itf_num;
-    usbd_edpt_xfer(rhport, ncm_interface.ep_notif, (uint8_t *) &ncm_notify_connected, sizeof(ncm_notify_connected));
-    ncm_interface.report_state = REPORT_DONE;
-    ncm_interface.report_pending = true;
+  if (ncm_interface.recv_glue_ntb == NULL) {
+    ncm_interface.recv_glue_ntb = recv_get_next_ready_ntb();
+    TU_LOG_DRV("  new buffer for glue logic: %p\n", ncm_interface.recv_glue_ntb);
+    ncm_interface.recv_glue_ntb_datagram_ndx = 0;
   }
-}
 
-TU_ATTR_WEAK void tud_network_link_state_cb(bool state)
-{
-  (void)state;
-}
+  if (ncm_interface.recv_glue_ntb != NULL) {
+    const ndp16_datagram_t *ndp16_datagram = (ndp16_datagram_t *) (ncm_interface.recv_glue_ntb->data + ncm_interface.recv_glue_ntb->nth.wNdpIndex + sizeof(ndp16_t));
 
-// Handle class control request
-// return false to stall control endpoint (e.g unsupported request)
-bool netd_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_control_request_t const * request)
-{
-  if ( stage != CONTROL_STAGE_SETUP ) return true;
+    if (ndp16_datagram[ncm_interface.recv_glue_ntb_datagram_ndx].wDatagramIndex == 0) {
+      TU_LOG_DRV("(EE) SOMETHING WENT WRONG 1\n");
+    } else if (ndp16_datagram[ncm_interface.recv_glue_ntb_datagram_ndx].wDatagramLength == 0) {
+      TU_LOG_DRV("(EE) SOMETHING WENT WRONG 2\n");
+    } else {
+      uint16_t datagramIndex = ndp16_datagram[ncm_interface.recv_glue_ntb_datagram_ndx].wDatagramIndex;
+      uint16_t datagramLength = ndp16_datagram[ncm_interface.recv_glue_ntb_datagram_ndx].wDatagramLength;
 
-  switch ( request->bmRequestType_bit.type )
-  {
-    case TUSB_REQ_TYPE_STANDARD:
-      switch ( request->bRequest )
-      {
-        case TUSB_REQ_GET_INTERFACE:
-        {
-          uint8_t const req_itfnum = (uint8_t) request->wIndex;
-          TU_VERIFY(ncm_interface.itf_num + 1 == req_itfnum);
+      TU_LOG_DRV("  recv[%d] - %d %d\n", ncm_interface.recv_glue_ntb_datagram_ndx, datagramIndex, datagramLength);
+      if (tud_network_recv_cb(ncm_interface.recv_glue_ntb->data + datagramIndex, datagramLength)) {
+        // send datagram successfully to glue logic
+        TU_LOG_DRV("    OK\n");
+        datagramIndex = ndp16_datagram[ncm_interface.recv_glue_ntb_datagram_ndx + 1].wDatagramIndex;
+        datagramLength = ndp16_datagram[ncm_interface.recv_glue_ntb_datagram_ndx + 1].wDatagramLength;
 
-          tud_control_xfer(rhport, request, &ncm_interface.itf_data_alt, 1);
+        if (datagramIndex != 0 && datagramLength != 0) {
+          // -> next datagram
+          ++ncm_interface.recv_glue_ntb_datagram_ndx;
+        } else {
+          // end of datagrams reached
+          recv_put_ntb_into_free_list(ncm_interface.recv_glue_ntb);
+          ncm_interface.recv_glue_ntb = NULL;
         }
-          break;
+      }
+    }
+  }
+} // recv_transfer_datagram_to_glue_logic
 
-        case TUSB_REQ_SET_INTERFACE:
-        {
-          uint8_t const req_itfnum = (uint8_t) request->wIndex;
-          uint8_t const req_alt    = (uint8_t) request->wValue;
+//-----------------------------------------------------------------------------
+//
+// all the tud_network_*() stuff (glue logic -> driver)
+//
 
-          // Only valid for Data Interface with Alternate is either 0 or 1
-          TU_VERIFY(ncm_interface.itf_num + 1 == req_itfnum && req_alt < 2);
+/**
+ * Check if the glue logic is allowed to call tud_network_xmit().
+ * This function also fetches a next buffer if required, so that tud_network_xmit() is ready for copy
+ * and transmission operation.
+ */
+bool tud_network_can_xmit(uint16_t size) {
+  TU_LOG_DRV("tud_network_can_xmit(%d)\n", size);
 
-          if (req_alt != ncm_interface.itf_data_alt) {
-            ncm_interface.itf_data_alt = req_alt;
+  TU_ASSERT(size <= CFG_TUD_NCM_OUT_NTB_MAX_SIZE - (sizeof(nth16_t) + sizeof(ndp16_t) + 2 * sizeof(ndp16_datagram_t)), false);
 
-            if (ncm_interface.itf_data_alt) {
-              if (!usbd_edpt_busy(rhport, ncm_interface.ep_out)) {
-                tud_network_recv_renew(); // prepare for incoming datagrams
-              }
-              if (!ncm_interface.report_pending) {
-                ncm_report();
-              }
-            }
+  if (xmit_requested_datagram_fits_into_current_ntb(size) || xmit_setup_next_glue_ntb()) {
+    // -> everything is fine
+    return true;
+  }
+  xmit_start_if_possible(ncm_interface.rhport);
+  TU_LOG_DRV("(II) tud_network_can_xmit: request blocked\n");// could happen if all xmit buffers are full (but should happen rarely)
+  return false;
+} // tud_network_can_xmit
 
-            tud_network_link_state_cb(ncm_interface.itf_data_alt);
-          }
+/**
+ * Put a datagram into a waiting NTB.
+ * If currently no transmission is started, then initiate transmission.
+ */
+void tud_network_xmit(void *ref, uint16_t arg) {
+  TU_LOG_DRV("tud_network_xmit(%p, %d)\n", ref, arg);
 
-          tud_control_status(rhport, request);
-        }
-          break;
+  if (ncm_interface.xmit_glue_ntb == NULL) {
+    TU_LOG_DRV("(EE) tud_network_xmit: no buffer\n");// must not happen (really)
+    return;
+  }
 
-          // unsupported request
-        default: return false;
-      }
-      break;
+  xmit_ntb_t *ntb = ncm_interface.xmit_glue_ntb;
 
-    case TUSB_REQ_TYPE_CLASS:
-      TU_VERIFY (ncm_interface.itf_num == request->wIndex);
+  // copy new datagram to the end of the current NTB
+  uint16_t size = tud_network_xmit_cb(ntb->data + ntb->nth.wBlockLength, ref, arg);
 
-      if (NCM_GET_NTB_PARAMETERS == request->bRequest)
-      {
-        tud_control_xfer(rhport, request, (void*)(uintptr_t) &ntb_parameters, sizeof(ntb_parameters));
-      }
+  // correct NTB internals
+  ntb->ndp_datagram[ncm_interface.xmit_glue_ntb_datagram_ndx].wDatagramIndex = ntb->nth.wBlockLength;
+  ntb->ndp_datagram[ncm_interface.xmit_glue_ntb_datagram_ndx].wDatagramLength = size;
+  ncm_interface.xmit_glue_ntb_datagram_ndx += 1;
 
-      break;
+  ntb->nth.wBlockLength += (uint16_t) (size + XMIT_ALIGN_OFFSET(size));
 
-      // unsupported request
-    default: return false;
+  if (ntb->nth.wBlockLength > CFG_TUD_NCM_OUT_NTB_MAX_SIZE) {
+    TU_LOG_DRV("(EE) tud_network_xmit: buffer overflow\n"); // must not happen (really)
+    return;
   }
 
-  return true;
-}
+  xmit_start_if_possible(ncm_interface.rhport);
+} // tud_network_xmit
 
-static void handle_incoming_datagram(uint32_t len)
-{
-  uint32_t size = len;
+/**
+ * Keep the receive logic busy and transfer pending packets to the glue logic.
+ */
+void tud_network_recv_renew(void) {
+  TU_LOG_DRV("tud_network_recv_renew()\n");
 
-  if (len == 0) {
-    return;
-  }
+  recv_transfer_datagram_to_glue_logic();
+  recv_try_to_start_new_reception(ncm_interface.rhport);
+} // tud_network_recv_renew
 
-  TU_ASSERT(size >= sizeof(nth16_t), );
+/**
+ * Same as tud_network_recv_renew() but knows \a rhport
+ */
+void tud_network_recv_renew_r(uint8_t rhport) {
+  TU_LOG_DRV("tud_network_recv_renew_r(%d)\n", rhport);
 
-  const nth16_t *hdr = (const nth16_t *)receive_ntb;
-  TU_ASSERT(hdr->dwSignature == NTH16_SIGNATURE, );
-  TU_ASSERT(hdr->wNdpIndex >= sizeof(nth16_t) && (hdr->wNdpIndex + sizeof(ndp16_t)) <= len, );
+  ncm_interface.rhport = rhport;
+  tud_network_recv_renew();
+} // tud_network_recv_renew
 
-  const ndp16_t *ndp = (const ndp16_t *)(receive_ntb + hdr->wNdpIndex);
-  TU_ASSERT(ndp->dwSignature == NDP16_SIGNATURE_NCM0 || ndp->dwSignature == NDP16_SIGNATURE_NCM1, );
-  TU_ASSERT(hdr->wNdpIndex + ndp->wLength <= len, );
+//-----------------------------------------------------------------------------
+//
+// all the netd_*() stuff (interface TinyUSB -> driver)
+//
+/**
+ * Initialize the driver data structures.
+ * Might be called several times.
+ */
+void netd_init(void) {
+  TU_LOG_DRV("netd_init()\n");
 
-  int num_datagrams = (ndp->wLength - 12) / 4;
-  ncm_interface.current_datagram_index = 0;
-  ncm_interface.num_datagrams = 0;
-  ncm_interface.ndp = ndp;
-  for (int i = 0; i < num_datagrams && ndp->datagram[i].wDatagramIndex && ndp->datagram[i].wDatagramLength; i++)
-  {
-    ncm_interface.num_datagrams++;
+  memset(&ncm_interface, 0, sizeof(ncm_interface));
+
+  for (int i = 0; i < XMIT_NTB_N; ++i) {
+    ncm_interface.xmit_free_ntb[i] = ncm_interface.xmit_ntb + i;
+  }
+  for (int i = 0; i < RECV_NTB_N; ++i) {
+    ncm_interface.recv_free_ntb[i] = ncm_interface.recv_ntb + i;
   }
+} // netd_init
 
-  tud_network_recv_renew();
+/**
+ * Deinit driver
+ */
+bool netd_deinit(void) {
+  return true;
 }
 
-bool netd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint32_t xferred_bytes)
-{
+/**
+ * Resets the port.
+ * In this driver this is the same as netd_init()
+ */
+void netd_reset(uint8_t rhport) {
   (void) rhport;
-  (void) result;
 
-  /* new datagram receive_ntb */
-  if (ep_addr == ncm_interface.ep_out )
-  {
-    handle_incoming_datagram(xferred_bytes);
-  }
+  netd_init();
+} // netd_reset
 
-  /* data transmission finished */
-  if (ep_addr == ncm_interface.ep_in )
-  {
-    if (ncm_interface.transferring) {
-      ncm_interface.transferring = false;
-    }
+/**
+ * Open the USB interface.
+ * - parse the USB descriptor \a TUD_CDC_NCM_DESCRIPTOR for itfnum and endpoints
+ * - a specific order of elements in the descriptor is tested.
+ *
+ * \note
+ *   Actually all of the information could be read directly from \a itf_desc, because the
+ *   structure and the values are well known.  But we do it this way.
+ *
+ * \post
+ * - \a itf_num set
+ * - \a ep_notif, \a ep_in and \a ep_out are set
+ * - USB interface is open
+ */
+uint16_t netd_open(uint8_t rhport, tusb_desc_interface_t const *itf_desc, uint16_t max_len) {
+  TU_ASSERT(ncm_interface.ep_notif == 0, 0);// assure that the interface is only opened once
 
-    // If there are datagrams queued up that we tried to send while this NTB was being emitted, send them now
-    if (ncm_interface.datagram_count && ncm_interface.itf_data_alt == 1) {
-      ncm_start_tx();
-    }
-  }
+  ncm_interface.itf_num = itf_desc->bInterfaceNumber;// management interface
 
-  if (ep_addr == ncm_interface.ep_notif )
-  {
-    ncm_interface.report_pending = false;
-    ncm_report();
+  // skip the two first entries and the following TUSB_DESC_CS_INTERFACE entries
+  uint16_t drv_len = sizeof(tusb_desc_interface_t);
+  uint8_t const *p_desc = tu_desc_next(itf_desc);
+  while (tu_desc_type(p_desc) == TUSB_DESC_CS_INTERFACE && drv_len <= max_len) {
+    drv_len += tu_desc_len(p_desc);
+    p_desc = tu_desc_next(p_desc);
   }
 
-  return true;
-}
+  // get notification endpoint
+  TU_ASSERT(tu_desc_type(p_desc) == TUSB_DESC_ENDPOINT, 0);
+  TU_ASSERT(usbd_edpt_open(rhport, (tusb_desc_endpoint_t const *) p_desc), 0);
+  ncm_interface.ep_notif = ((tusb_desc_endpoint_t const *) p_desc)->bEndpointAddress;
+  drv_len += tu_desc_len(p_desc);
+  p_desc = tu_desc_next(p_desc);
 
-// poll network driver for its ability to accept another packet to transmit
-bool tud_network_can_xmit(uint16_t size)
-{
-  TU_VERIFY(ncm_interface.itf_data_alt == 1);
+  // skip the following TUSB_DESC_INTERFACE entries (which must be TUSB_CLASS_CDC_DATA)
+  while (tu_desc_type(p_desc) == TUSB_DESC_INTERFACE && drv_len <= max_len) {
+    tusb_desc_interface_t const *data_itf_desc = (tusb_desc_interface_t const *) p_desc;
+    TU_ASSERT(data_itf_desc->bInterfaceClass == TUSB_CLASS_CDC_DATA, 0);
 
-  if (ncm_interface.datagram_count >= ncm_interface.max_datagrams_per_ntb) {
-    TU_LOG_DRV("NTB full [by count]\r\n");
-    return false;
+    drv_len += tu_desc_len(p_desc);
+    p_desc = tu_desc_next(p_desc);
   }
 
-  size_t next_datagram_offset = ncm_interface.next_datagram_offset;
-  if (next_datagram_offset + size > ncm_interface.ntb_in_size) {
-    TU_LOG_DRV("ntb full [by size]\r\n");
-    return false;
+  // a TUSB_DESC_ENDPOINT (actually two) must follow, open these endpoints
+  TU_ASSERT(tu_desc_type(p_desc) == TUSB_DESC_ENDPOINT, 0);
+  TU_ASSERT(usbd_open_edpt_pair(rhport, p_desc, 2, TUSB_XFER_BULK, &ncm_interface.ep_out, &ncm_interface.ep_in));
+  drv_len += 2 * sizeof(tusb_desc_endpoint_t);
+
+  return drv_len;
+} // netd_open
+
+/**
+ * Handle TinyUSB requests to process transfer events.
+ */
+bool netd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint32_t xferred_bytes) {
+  (void) result;
+
+  if (ep_addr == ncm_interface.ep_out) {
+    // new NTB received
+    // - make the NTB valid
+    // - if ready transfer datagrams to the glue logic for further processing
+    // - if there is a free receive buffer, initiate reception
+    if (!recv_validate_datagram(ncm_interface.recv_tinyusb_ntb, xferred_bytes)) {
+      // verification failed: ignore NTB and return it to free
+      TU_LOG_DRV("(EE) VALIDATION FAILED. WHAT CAN WE DO IN THIS CASE?\n");
+    } else {
+      // packet ok -> put it into ready list
+      recv_put_ntb_into_ready_list(ncm_interface.recv_tinyusb_ntb);
+    }
+    ncm_interface.recv_tinyusb_ntb = NULL;
+    tud_network_recv_renew_r(rhport);
+  } else if (ep_addr == ncm_interface.ep_in) {
+    // transmission of an NTB finished
+    // - free the transmitted NTB buffer
+    // - insert ZLPs when necessary
+    // - if there is another transmit NTB waiting, try to start transmission
+    xmit_put_ntb_into_free_list(ncm_interface.xmit_tinyusb_ntb);
+    ncm_interface.xmit_tinyusb_ntb = NULL;
+    if (!xmit_insert_required_zlp(rhport, xferred_bytes)) {
+      xmit_start_if_possible(rhport);
+    }
+  } else if (ep_addr == ncm_interface.ep_notif) {
+    // next transfer on notification channel
+    notification_xmit(rhport, true);
   }
 
   return true;
-}
+} // netd_xfer_cb
 
-void tud_network_xmit(void *ref, uint16_t arg)
-{
-  transmit_ntb_t *ntb = &transmit_ntb[ncm_interface.current_ntb];
-  size_t next_datagram_offset = ncm_interface.next_datagram_offset;
+/**
+ * Respond to TinyUSB control requests.
+ * At startup transmission of notification packets are done here.
+ */
+bool netd_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_control_request_t const *request) {
+  if (stage != CONTROL_STAGE_SETUP) {
+    return true;
+  }
 
-  uint16_t size = tud_network_xmit_cb(ntb->data + next_datagram_offset, ref, arg);
+  switch (request->bmRequestType_bit.type) {
+    case TUSB_REQ_TYPE_STANDARD:
 
-  ntb->ndp.datagram[ncm_interface.datagram_count].wDatagramIndex = ncm_interface.next_datagram_offset;
-  ntb->ndp.datagram[ncm_interface.datagram_count].wDatagramLength = size;
+      switch (request->bRequest) {
+        case TUSB_REQ_GET_INTERFACE: {
+          TU_VERIFY(ncm_interface.itf_num + 1 == request->wIndex, false);
 
-  ncm_interface.datagram_count++;
-  next_datagram_offset += size;
+          tud_control_xfer(rhport, request, &ncm_interface.itf_data_alt, 1);
+        } break;
 
-  // round up so the next datagram is aligned correctly
-  next_datagram_offset += (CFG_TUD_NCM_ALIGNMENT - 1);
-  next_datagram_offset -= (next_datagram_offset % CFG_TUD_NCM_ALIGNMENT);
+        case TUSB_REQ_SET_INTERFACE: {
+          TU_VERIFY(ncm_interface.itf_num + 1 == request->wIndex && request->wValue < 2, false);
 
-  ncm_interface.next_datagram_offset = next_datagram_offset;
+          ncm_interface.itf_data_alt = (uint8_t) request->wValue;
 
-  ncm_start_tx();
-}
+          if (ncm_interface.itf_data_alt == 1) {
+            tud_network_recv_renew_r(rhport);
+            notification_xmit(rhport, false);
+          }
+          tud_control_status(rhport, request);
+        } break;
 
-#endif
+        // unsupported request
+        default:
+          return false;
+      }
+      break;
+
+    case TUSB_REQ_TYPE_CLASS:
+      TU_VERIFY(ncm_interface.itf_num == request->wIndex, false);
+      switch (request->bRequest) {
+        case NCM_GET_NTB_PARAMETERS: {
+          // transfer NTB parameters to host.
+          tud_control_xfer(rhport, request, (void *) (uintptr_t) &ntb_parameters, sizeof(ntb_parameters));
+        } break;
+
+          // unsupported request
+        default:
+          return false;
+      }
+      break;
+      // unsupported request
+    default:
+      return false;
+  }
+
+  return true;
+} // netd_control_xfer_cb
+
+#endif // ( CFG_TUD_ENABLED && CFG_TUD_NCM )
diff --git a/src/class/net/net_device.h b/src/class/net/net_device.h
index da1a7b1e8..0665d547c 100644
--- a/src/class/net/net_device.h
+++ b/src/class/net/net_device.h
@@ -28,14 +28,13 @@
 #ifndef _TUSB_NET_DEVICE_H_
 #define _TUSB_NET_DEVICE_H_
 
+#include <stdint.h>
 #include "class/cdc/cdc.h"
 
 #if CFG_TUD_ECM_RNDIS && CFG_TUD_NCM
 #error "Cannot enable both ECM_RNDIS and NCM network drivers"
 #endif
 
-#include "ncm.h"
-
 /* declared here, NOT in usb_descriptors.c, so that the driver can intelligently ZLP as needed */
 #define CFG_TUD_NET_ENDPOINT_SIZE (TUD_OPT_HIGH_SPEED ? 512 : 64)
 
@@ -44,21 +43,13 @@
 #define CFG_TUD_NET_MTU           1514
 #endif
 
-#ifndef CFG_TUD_NCM_IN_NTB_MAX_SIZE
-#define CFG_TUD_NCM_IN_NTB_MAX_SIZE 3200
-#endif
 
-#ifndef CFG_TUD_NCM_OUT_NTB_MAX_SIZE
-#define CFG_TUD_NCM_OUT_NTB_MAX_SIZE 3200
-#endif
+// Table 4.3 Data Class Interface Protocol Codes
+typedef enum
+{
+  NCM_DATA_PROTOCOL_NETWORK_TRANSFER_BLOCK = 0x01
+} ncm_data_interface_protocol_code_t;
 
-#ifndef CFG_TUD_NCM_MAX_DATAGRAMS_PER_NTB
-#define CFG_TUD_NCM_MAX_DATAGRAMS_PER_NTB 8
-#endif
-
-#ifndef CFG_TUD_NCM_ALIGNMENT
-#define CFG_TUD_NCM_ALIGNMENT 4
-#endif
 
 #ifdef __cplusplus
  extern "C" {
@@ -96,8 +87,6 @@ void tud_network_init_cb(void);
 // TODO removed later since it is not part of tinyusb stack
 extern uint8_t tud_network_mac_address[6];
 
-//------------- NCM -------------//
-
 // callback to client providing optional indication of internal state of network driver
 void tud_network_link_state_cb(bool state);