src/class/msc/msc_device.c

/*
 * 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.
 *
 * This file is part of the TinyUSB stack.
 */

#include "tusb_option.h"

#if (TUSB_OPT_DEVICE_ENABLED && CFG_TUD_MSC)

#include "device/usbd.h"
#include "device/usbd_pvt.h"
#include "device/dcd.h"         // for faking dcd_event_xfer_complete

#include "msc_device.h"

//--------------------------------------------------------------------+
// MACRO CONSTANT TYPEDEF
//--------------------------------------------------------------------+

// Can be selectively disabled to reduce logging when troubleshooting other driver
#define MSC_DEBUG   2

enum
{
  MSC_STAGE_CMD  = 0,
  MSC_STAGE_DATA,
  MSC_STAGE_STATUS,
  MSC_STAGE_STATUS_SENT,
  MSC_STAGE_NEED_RESET,
};

typedef struct
{
  // TODO optimize alignment
  CFG_TUSB_MEM_ALIGN msc_cbw_t cbw;
  CFG_TUSB_MEM_ALIGN msc_csw_t csw;

  uint8_t  itf_num;
  uint8_t  ep_in;
  uint8_t  ep_out;

  // Bulk Only Transfer (BOT) Protocol
  uint8_t  stage;
  uint32_t total_len;   // byte to be transferred, can be smaller than total_bytes in cbw
  uint32_t xferred_len; // numbered of bytes transferred so far in the Data Stage

  // Sense Response Data
  uint8_t sense_key;
  uint8_t add_sense_code;
  uint8_t add_sense_qualifier;
}mscd_interface_t;

CFG_TUSB_MEM_SECTION CFG_TUSB_MEM_ALIGN static mscd_interface_t _mscd_itf;
CFG_TUSB_MEM_SECTION CFG_TUSB_MEM_ALIGN static uint8_t _mscd_buf[CFG_TUD_MSC_EP_BUFSIZE];

//--------------------------------------------------------------------+
// INTERNAL OBJECT & FUNCTION DECLARATION
//--------------------------------------------------------------------+
static int32_t proc_builtin_scsi(uint8_t lun, uint8_t const scsi_cmd[16], uint8_t* buffer, uint32_t bufsize);
static void proc_read10_cmd(uint8_t rhport, mscd_interface_t* p_msc);

static void proc_write10_cmd(uint8_t rhport, mscd_interface_t* p_msc);
static void proc_write10_new_data(uint8_t rhport, mscd_interface_t* p_msc, uint32_t xferred_bytes);

TU_ATTR_ALWAYS_INLINE static inline bool is_data_in(uint8_t dir)
{
  return tu_bit_test(dir, 7);
}

static inline bool send_csw(uint8_t rhport, mscd_interface_t* p_msc)
{
  // Data residue is always = host expect - actual transferred
  p_msc->csw.data_residue = p_msc->cbw.total_bytes - p_msc->xferred_len;

  p_msc->stage = MSC_STAGE_STATUS_SENT;
  return usbd_edpt_xfer(rhport, p_msc->ep_in , (uint8_t*) &p_msc->csw, sizeof(msc_csw_t));
}

static inline bool prepare_cbw(uint8_t rhport, mscd_interface_t* p_msc)
{
  p_msc->stage = MSC_STAGE_CMD;
  return usbd_edpt_xfer(rhport, p_msc->ep_out, (uint8_t*) &p_msc->cbw, sizeof(msc_cbw_t));
}

static void fail_scsi_op(uint8_t rhport, mscd_interface_t* p_msc, uint8_t status)
{
  msc_cbw_t const * p_cbw = &p_msc->cbw;
  msc_csw_t       * p_csw = &p_msc->csw;

  p_csw->status       = status;
  p_csw->data_residue = p_msc->cbw.total_bytes - p_msc->xferred_len;
  p_msc->stage        = MSC_STAGE_STATUS;

  // failed but sense key is not set: default to Illegal Request
  if ( p_msc->sense_key == 0 ) tud_msc_set_sense(p_cbw->lun, SCSI_SENSE_ILLEGAL_REQUEST, 0x20, 0x00);

  // If there is data stage and not yet complete, stall it
  if ( p_cbw->total_bytes && p_csw->data_residue )
  {
    if ( is_data_in(p_cbw->dir) )
    {
      usbd_edpt_stall(rhport, p_msc->ep_in);
    }
    else
    {
      usbd_edpt_stall(rhport, p_msc->ep_out);
    }
  }
}

static inline uint32_t rdwr10_get_lba(uint8_t const command[])
{
  // use offsetof to avoid pointer to the odd/unaligned address
  uint32_t const lba = tu_unaligned_read32(command + offsetof(scsi_write10_t, lba));

  // lba is in Big Endian
  return tu_ntohl(lba);
}

static inline uint16_t rdwr10_get_blockcount(msc_cbw_t const* cbw)
{
  uint16_t const block_count = tu_unaligned_read16(cbw->command + offsetof(scsi_write10_t, block_count));
  return tu_ntohs(block_count);
}

static inline uint16_t rdwr10_get_blocksize(msc_cbw_t const* cbw)
{
  // first extract block count in the command
  uint16_t const block_count = rdwr10_get_blockcount(cbw);

  // invalid block count
  if (block_count == 0) return 0;

  return (uint16_t) (cbw->total_bytes / block_count);
}

uint8_t rdwr10_validate_cmd(msc_cbw_t const* cbw)
{
  uint8_t status = MSC_CSW_STATUS_PASSED;
  uint16_t const block_count = rdwr10_get_blockcount(cbw);

  if ( cbw->total_bytes == 0 )
  {
    if ( block_count )
    {
      TU_LOG(MSC_DEBUG, "  SCSI case 2 (Hn < Di) or case 3 (Hn < Do) \r\n");
      status = MSC_CSW_STATUS_PHASE_ERROR;
    }else
    {
      // no data transfer, only exist in complaint test suite
    }
  }else
  {
    if ( SCSI_CMD_READ_10 == cbw->command[0] && !is_data_in(cbw->dir) )
    {
      TU_LOG(MSC_DEBUG, "  SCSI case 10 (Ho <> Di)\r\n");
      status = MSC_CSW_STATUS_PHASE_ERROR;
    }
    else if ( SCSI_CMD_WRITE_10 == cbw->command[0] && is_data_in(cbw->dir) )
    {
      TU_LOG(MSC_DEBUG, "  SCSI case 8 (Hi <> Do)\r\n");
      status = MSC_CSW_STATUS_PHASE_ERROR;
    }
    else if ( 0 == block_count )
    {
      TU_LOG(MSC_DEBUG, "  SCSI case 4 Hi > Dn (READ10) or case 9 Ho > Dn (WRITE10) \r\n");
      status =  MSC_CSW_STATUS_FAILED;
    }
    else if ( cbw->total_bytes / block_count == 0 )
    {
      TU_LOG(MSC_DEBUG, " Computed block size = 0. SCSI case 7 Hi < Di (READ10) or case 13 Ho < Do (WRIT10)\r\n");
      status = MSC_CSW_STATUS_PHASE_ERROR;
    }
  }

  return status;
}

//--------------------------------------------------------------------+
// Debug
//--------------------------------------------------------------------+
#if CFG_TUSB_DEBUG >= 2

TU_ATTR_UNUSED static tu_lookup_entry_t const _msc_scsi_cmd_lookup[] =
{
  { .key = SCSI_CMD_TEST_UNIT_READY              , .data = "Test Unit Ready" },
  { .key = SCSI_CMD_INQUIRY                      , .data = "Inquiry" },
  { .key = SCSI_CMD_MODE_SELECT_6                , .data = "Mode_Select 6" },
  { .key = SCSI_CMD_MODE_SENSE_6                 , .data = "Mode_Sense 6" },
  { .key = SCSI_CMD_START_STOP_UNIT              , .data = "Start Stop Unit" },
  { .key = SCSI_CMD_PREVENT_ALLOW_MEDIUM_REMOVAL , .data = "Prevent Allow Medium Removal" },
  { .key = SCSI_CMD_READ_CAPACITY_10             , .data = "Read Capacity10" },
  { .key = SCSI_CMD_REQUEST_SENSE                , .data = "Request Sense" },
  { .key = SCSI_CMD_READ_FORMAT_CAPACITY         , .data = "Read Format Capacity" },
  { .key = SCSI_CMD_READ_10                      , .data = "Read10" },
  { .key = SCSI_CMD_WRITE_10                     , .data = "Write10" }
};

TU_ATTR_UNUSED static tu_lookup_table_t const _msc_scsi_cmd_table =
{
  .count = TU_ARRAY_SIZE(_msc_scsi_cmd_lookup),
  .items = _msc_scsi_cmd_lookup
};

#endif

//--------------------------------------------------------------------+
// APPLICATION API
//--------------------------------------------------------------------+
bool tud_msc_set_sense(uint8_t lun, uint8_t sense_key, uint8_t add_sense_code, uint8_t add_sense_qualifier)
{
  (void) lun;

  _mscd_itf.sense_key           = sense_key;
  _mscd_itf.add_sense_code      = add_sense_code;
  _mscd_itf.add_sense_qualifier = add_sense_qualifier;

  return true;
}

//--------------------------------------------------------------------+
// USBD Driver API
//--------------------------------------------------------------------+
void mscd_init(void)
{
  tu_memclr(&_mscd_itf, sizeof(mscd_interface_t));
}

void mscd_reset(uint8_t rhport)
{
  (void) rhport;
  tu_memclr(&_mscd_itf, sizeof(mscd_interface_t));
}

uint16_t mscd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t max_len)
{
  // only support SCSI's BOT protocol
  TU_VERIFY(TUSB_CLASS_MSC    == itf_desc->bInterfaceClass &&
            MSC_SUBCLASS_SCSI == itf_desc->bInterfaceSubClass &&
            MSC_PROTOCOL_BOT  == itf_desc->bInterfaceProtocol, 0);

  // msc driver length is fixed
  uint16_t const drv_len = sizeof(tusb_desc_interface_t) + 2*sizeof(tusb_desc_endpoint_t);

  // Max length must be at least 1 interface + 2 endpoints
  TU_ASSERT(max_len >= drv_len, 0);

  mscd_interface_t * p_msc = &_mscd_itf;
  p_msc->itf_num = itf_desc->bInterfaceNumber;

  // Open endpoint pair
  TU_ASSERT( usbd_open_edpt_pair(rhport, tu_desc_next(itf_desc), 2, TUSB_XFER_BULK, &p_msc->ep_out, &p_msc->ep_in), 0 );

  // Prepare for Command Block Wrapper
  TU_ASSERT( prepare_cbw(rhport, p_msc), drv_len);

  return drv_len;
}

static void proc_bot_reset(mscd_interface_t* p_msc)
{
  p_msc->stage       = MSC_STAGE_CMD;
  p_msc->total_len   = 0;
  p_msc->xferred_len = 0;

  p_msc->sense_key           = 0;
  p_msc->add_sense_code      = 0;
  p_msc->add_sense_qualifier = 0;
}

// Invoked when a control transfer occurred on an interface of this class
// Driver response accordingly to the request and the transfer stage (setup/data/ack)
// return false to stall control endpoint (e.g unsupported request)
bool mscd_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_control_request_t const * request)
{
  // nothing to do with DATA & ACK stage
  if (stage != CONTROL_STAGE_SETUP) return true;

  mscd_interface_t* p_msc = &_mscd_itf;

  // Clear Endpoint Feature (stall) for recovery
  if ( TUSB_REQ_TYPE_STANDARD     == request->bmRequestType_bit.type      &&
       TUSB_REQ_RCPT_ENDPOINT     == request->bmRequestType_bit.recipient &&
       TUSB_REQ_CLEAR_FEATURE     == request->bRequest                    &&
       TUSB_REQ_FEATURE_EDPT_HALT == request->wValue )
  {
    uint8_t const ep_addr = tu_u16_low(request->wIndex);

    if ( p_msc->stage == MSC_STAGE_NEED_RESET )
    {
      // reset recovery is required to recover from this stage
      // Clear Stall request cannot resolve this -> continue to stall endpoint
      usbd_edpt_stall(rhport, ep_addr);
    }
    else
    {
      if ( ep_addr == p_msc->ep_in )
      {
        if ( p_msc->stage == MSC_STAGE_STATUS )
        {
          // resume sending SCSI status if we are in this stage previously before stalled
          TU_ASSERT( send_csw(rhport, p_msc) );
        }
      }
      else if ( ep_addr == p_msc->ep_out )
      {
        if ( p_msc->stage == MSC_STAGE_CMD )
        {
          // part of reset recovery (probably due to invalid CBW) -> prepare for new command
          // Note: skip if already queued previously
          if ( usbd_edpt_ready(rhport, p_msc->ep_out) )
          {
            TU_ASSERT( prepare_cbw(rhport, p_msc) );
          }
        }
      }
    }

    return true;
  }

  // From this point only handle class request only
  TU_VERIFY(request->bmRequestType_bit.type == TUSB_REQ_TYPE_CLASS);

  switch ( request->bRequest )
  {
    case MSC_REQ_RESET:
      TU_LOG(MSC_DEBUG, "  MSC BOT Reset\r\n");
      TU_VERIFY(request->wValue == 0 && request->wLength == 0);

      // driver state reset
      proc_bot_reset(p_msc);

      tud_control_status(rhport, request);
    break;

    case MSC_REQ_GET_MAX_LUN:
    {
      TU_LOG(MSC_DEBUG, "  MSC Get Max Lun\r\n");
      TU_VERIFY(request->wValue == 0 && request->wLength == 1);

      uint8_t maxlun = 1;
      if (tud_msc_get_maxlun_cb) maxlun = tud_msc_get_maxlun_cb();
      TU_VERIFY(maxlun);

      // MAX LUN is minus 1 by specs
      maxlun--;

      tud_control_xfer(rhport, request, &maxlun, 1);
    }
    break;

    default: return false; // stall unsupported request
  }

  return true;
}

bool mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes)
{
  (void) event;

  mscd_interface_t* p_msc = &_mscd_itf;
  msc_cbw_t const * p_cbw = &p_msc->cbw;
  msc_csw_t       * p_csw = &p_msc->csw;

  switch (p_msc->stage)
  {
    case MSC_STAGE_CMD:
      //------------- new CBW received -------------//
      // Complete IN while waiting for CMD is usually Status of previous SCSI op, ignore it
      if(ep_addr != p_msc->ep_out) return true;

      if ( !(xferred_bytes == sizeof(msc_cbw_t) && p_cbw->signature == MSC_CBW_SIGNATURE) )
      {
        TU_LOG(MSC_DEBUG, "  SCSI CBW is not valid\r\n");

        // BOT 6.6.1 If CBW is not valid stall both endpoints until reset recovery
        p_msc->stage = MSC_STAGE_NEED_RESET;

        // invalid CBW stall both endpoints
        usbd_edpt_stall(rhport, p_msc->ep_in);
        usbd_edpt_stall(rhport, p_msc->ep_out);

        return false;
      }

      TU_LOG(MSC_DEBUG, "  SCSI Command: %s\r\n", tu_lookup_find(&_msc_scsi_cmd_table, p_cbw->command[0]));
      //TU_LOG_MEM(MSC_DEBUG, p_cbw, xferred_bytes, 2);

      p_csw->signature    = MSC_CSW_SIGNATURE;
      p_csw->tag          = p_cbw->tag;
      p_csw->data_residue = 0;
      p_csw->status       = MSC_CSW_STATUS_PASSED;

      /*------------- Parse command and prepare DATA -------------*/
      p_msc->stage = MSC_STAGE_DATA;
      p_msc->total_len = p_cbw->total_bytes;
      p_msc->xferred_len = 0;

      // Read10 or Write10
      if ( (SCSI_CMD_READ_10 == p_cbw->command[0]) || (SCSI_CMD_WRITE_10 == p_cbw->command[0]) )
      {
        uint8_t const status = rdwr10_validate_cmd(p_cbw);

        if ( status != MSC_CSW_STATUS_PASSED)
        {
          fail_scsi_op(rhport, p_msc, status);
        }else if ( p_cbw->total_bytes )
        {
          if (SCSI_CMD_READ_10 == p_cbw->command[0])
          {
            proc_read10_cmd(rhport, p_msc);
          }else
          {
            proc_write10_cmd(rhport, p_msc);
          }
        }else
        {
          // no data transfer, only exist in complaint test suite
          p_msc->stage = MSC_STAGE_STATUS;
        }
      }
      else
      {
        // For other SCSI commands
        // 1. OUT : queue transfer (invoke app callback after done)
        // 2. IN & Zero: Process if is built-in, else Invoke app callback. Skip DATA if zero length
        if ( (p_cbw->total_bytes > 0 ) && !is_data_in(p_cbw->dir) )
        {
          if (p_cbw->total_bytes > sizeof(_mscd_buf))
          {
            TU_LOG(MSC_DEBUG, "  SCSI reject non READ10/WRITE10 with large data\r\n");
            fail_scsi_op(rhport, p_msc, MSC_CSW_STATUS_FAILED);
          }else
          {
            // Didn't check for case 9 (Ho > Dn), which requires examining scsi command first
            // but it is OK to just receive data then responded with failed status
            TU_ASSERT( usbd_edpt_xfer(rhport, p_msc->ep_out, _mscd_buf, p_msc->total_len) );
          }
        }else
        {
          // First process if it is a built-in commands
          int32_t resplen = proc_builtin_scsi(p_cbw->lun, p_cbw->command, _mscd_buf, sizeof(_mscd_buf));

          // Invoke user callback if not built-in
          if ( (resplen < 0) && (p_msc->sense_key == 0) )
          {
            resplen = tud_msc_scsi_cb(p_cbw->lun, p_cbw->command, _mscd_buf, p_msc->total_len);
          }

          if ( resplen < 0 )
          {
            // unsupported command
            TU_LOG(MSC_DEBUG, "  SCSI unsupported command\r\n");
            fail_scsi_op(rhport, p_msc, MSC_CSW_STATUS_FAILED);
          }
          else if (resplen == 0)
          {
            if (p_cbw->total_bytes)
            {
              // 6.7 The 13 Cases: case 4 (Hi > Dn)
              // TU_LOG(MSC_DEBUG, "  SCSI case 4 (Hi > Dn): %lu\r\n", p_cbw->total_bytes);
              fail_scsi_op(rhport, p_msc, MSC_CSW_STATUS_FAILED);
            }else
            {
              // case 1 Hn = Dn: all good
              p_msc->stage = MSC_STAGE_STATUS;
            }
          }
          else
          {
            if ( p_cbw->total_bytes == 0 )
            {
              // 6.7 The 13 Cases: case 2 (Hn < Di)
              // TU_LOG(MSC_DEBUG, "  SCSI case 2 (Hn < Di): %lu\r\n", p_cbw->total_bytes);
              fail_scsi_op(rhport, p_msc, MSC_CSW_STATUS_FAILED);
            }else
            {
              // cannot return more than host expect
              p_msc->total_len = tu_min32((uint32_t) resplen, p_cbw->total_bytes);
              TU_ASSERT( usbd_edpt_xfer(rhport, p_msc->ep_in, _mscd_buf, p_msc->total_len) );
            }
          }
        }
      }
    break;

    case MSC_STAGE_DATA:
      TU_LOG(MSC_DEBUG, "  SCSI Data\r\n");
      //TU_LOG_MEM(MSC_DEBUG, _mscd_buf, xferred_bytes, 2);

      if (SCSI_CMD_READ_10 == p_cbw->command[0])
      {
        p_msc->xferred_len += xferred_bytes;

        if ( p_msc->xferred_len >= p_msc->total_len )
        {
          // Data Stage is complete
          p_msc->stage = MSC_STAGE_STATUS;
        }else
        {
          proc_read10_cmd(rhport, p_msc);
        }
      }
      else if (SCSI_CMD_WRITE_10 == p_cbw->command[0])
      {
        proc_write10_new_data(rhport, p_msc, xferred_bytes);
      }
      else
      {
        p_msc->xferred_len += xferred_bytes;

        // OUT transfer, invoke callback if needed
        if ( !is_data_in(p_cbw->dir) )
        {
          int32_t cb_result = tud_msc_scsi_cb(p_cbw->lun, p_cbw->command, _mscd_buf, p_msc->total_len);

          if ( cb_result < 0 )
          {
            // unsupported command
            TU_LOG(MSC_DEBUG, "  SCSI unsupported command\r\n");
            fail_scsi_op(rhport, p_msc, MSC_CSW_STATUS_FAILED);
          }else
          {
            // TODO haven't implement this scenario any further yet
          }
        }

        if ( p_msc->xferred_len >= p_msc->total_len )
        {
          // Data Stage is complete
          p_msc->stage = MSC_STAGE_STATUS;
        }
        else
        {
          // This scenario with command that take more than one transfer is already rejected at Command stage
          TU_BREAKPOINT();
        }
      }
    break;

    case MSC_STAGE_STATUS:
      // processed immediately after this switch, supposedly to be empty
    break;

    case MSC_STAGE_STATUS_SENT:
      // Wait for the Status phase to complete
      if( (ep_addr == p_msc->ep_in) && (xferred_bytes == sizeof(msc_csw_t)) )
      {
        TU_LOG(MSC_DEBUG, "  SCSI Status = %u\r\n", p_csw->status);
        // TU_LOG_MEM(MSC_DEBUG, p_csw, xferred_bytes, 2);

        // Invoke complete callback if defined
        // Note: There is racing issue with samd51 + qspi flash testing with arduino
        // if complete_cb() is invoked after queuing the status.
        switch(p_cbw->command[0])
        {
          case SCSI_CMD_READ_10:
            if ( tud_msc_read10_complete_cb ) tud_msc_read10_complete_cb(p_cbw->lun);
          break;

          case SCSI_CMD_WRITE_10:
            if ( tud_msc_write10_complete_cb ) tud_msc_write10_complete_cb(p_cbw->lun);
          break;

          default:
            if ( tud_msc_scsi_complete_cb ) tud_msc_scsi_complete_cb(p_cbw->lun, p_cbw->command);
          break;
        }

        TU_ASSERT( prepare_cbw(rhport, p_msc) );
      }else
      {
        // Any xfer ended here is consider unknown error, ignore it
        TU_LOG1("  Warning expect SCSI Status but received unknown data\r\n");
      }
    break;

    default : break;
  }

  if ( p_msc->stage == MSC_STAGE_STATUS )
  {
    // skip status if epin is currently stalled, will do it when received Clear Stall request
    if ( !usbd_edpt_stalled(rhport,  p_msc->ep_in) )
    {
      if ( (p_cbw->total_bytes > p_msc->xferred_len) && is_data_in(p_cbw->dir) )
      {
        // 6.7 The 13 Cases: case 5 (Hi > Di): STALL before status
        // TU_LOG(MSC_DEBUG, "  SCSI case 5 (Hi > Di): %lu > %lu\r\n", p_cbw->total_bytes, p_msc->xferred_len);
        usbd_edpt_stall(rhport, p_msc->ep_in);
      }else
      {
        TU_ASSERT( send_csw(rhport, p_msc) );
      }
    }

    #if TU_CHECK_MCU(OPT_MCU_CXD56)
    // WORKAROUND: cxd56 has its own nuttx usb stack which does not forward Set/ClearFeature(Endpoint) to DCD.
    // There is no way for us to know when EP is un-stall, therefore we will unconditionally un-stall here and
    // hope everything will work
    if ( usbd_edpt_stalled(rhport, p_msc->ep_in) )
    {
      usbd_edpt_clear_stall(rhport, p_msc->ep_in);
      send_csw(rhport, p_msc);
    }
    #endif
  }

  return true;
}

/*------------------------------------------------------------------*/
/* SCSI Command Process
 *------------------------------------------------------------------*/

// return response's length (copied to buffer). Negative if it is not an built-in command or indicate Failed status (CSW)
// In case of a failed status, sense key must be set for reason of failure
static int32_t proc_builtin_scsi(uint8_t lun, uint8_t const scsi_cmd[16], uint8_t* buffer, uint32_t bufsize)
{
  (void) bufsize; // TODO refractor later
  int32_t resplen;

  mscd_interface_t* p_msc = &_mscd_itf;

  switch ( scsi_cmd[0] )
  {
    case SCSI_CMD_TEST_UNIT_READY:
      resplen = 0;
      if ( !tud_msc_test_unit_ready_cb(lun) )
      {
        // Failed status response
        resplen = - 1;

        // If sense key is not set by callback, default to Logical Unit Not Ready, Cause Not Reportable
        if ( p_msc->sense_key == 0 ) tud_msc_set_sense(lun, SCSI_SENSE_NOT_READY, 0x04, 0x00);
      }
    break;

    case SCSI_CMD_START_STOP_UNIT:
      resplen = 0;

      if (tud_msc_start_stop_cb)
      {
        scsi_start_stop_unit_t const * start_stop = (scsi_start_stop_unit_t const *) scsi_cmd;
        if ( !tud_msc_start_stop_cb(lun, start_stop->power_condition, start_stop->start, start_stop->load_eject) )
        {
          // Failed status response
          resplen = - 1;

          // If sense key is not set by callback, default to Logical Unit Not Ready, Cause Not Reportable
          if ( p_msc->sense_key == 0 ) tud_msc_set_sense(lun, SCSI_SENSE_NOT_READY, 0x04, 0x00);
        }
      }
    break;

    case SCSI_CMD_READ_CAPACITY_10:
    {
      uint32_t block_count;
      uint32_t block_size;
      uint16_t block_size_u16;

      tud_msc_capacity_cb(lun, &block_count, &block_size_u16);
      block_size = (uint32_t) block_size_u16;

      // Invalid block size/count from callback, possibly unit is not ready
      // stall this request, set sense key to NOT READY
      if (block_count == 0 || block_size == 0)
      {
        resplen = -1;

        // If sense key is not set by callback, default to Logical Unit Not Ready, Cause Not Reportable
        if ( p_msc->sense_key == 0 ) tud_msc_set_sense(lun, SCSI_SENSE_NOT_READY, 0x04, 0x00);
      }else
      {
        scsi_read_capacity10_resp_t read_capa10;

        read_capa10.last_lba = tu_htonl(block_count-1);
        read_capa10.block_size = tu_htonl(block_size);

        resplen = sizeof(read_capa10);
        memcpy(buffer, &read_capa10, resplen);
      }
    }
    break;

    case SCSI_CMD_READ_FORMAT_CAPACITY:
    {
      scsi_read_format_capacity_data_t read_fmt_capa =
      {
          .list_length     = 8,
          .block_num       = 0,
          .descriptor_type = 2, // formatted media
          .block_size_u16  = 0
      };

      uint32_t block_count;
      uint16_t block_size;

      tud_msc_capacity_cb(lun, &block_count, &block_size);

      // Invalid block size/count from callback, possibly unit is not ready
      // stall this request, set sense key to NOT READY
      if (block_count == 0 || block_size == 0)
      {
        resplen = -1;

        // If sense key is not set by callback, default to Logical Unit Not Ready, Cause Not Reportable
        if ( p_msc->sense_key == 0 ) tud_msc_set_sense(lun, SCSI_SENSE_NOT_READY, 0x04, 0x00);
      }else
      {
        read_fmt_capa.block_num = tu_htonl(block_count);
        read_fmt_capa.block_size_u16 = tu_htons(block_size);

        resplen = sizeof(read_fmt_capa);
        memcpy(buffer, &read_fmt_capa, resplen);
      }
    }
    break;

    case SCSI_CMD_INQUIRY:
    {
      scsi_inquiry_resp_t inquiry_rsp =
      {
          .is_removable         = 1,
          .version              = 2,
          .response_data_format = 2,
      };

      // vendor_id, product_id, product_rev is space padded string
      memset(inquiry_rsp.vendor_id  , ' ', sizeof(inquiry_rsp.vendor_id));
      memset(inquiry_rsp.product_id , ' ', sizeof(inquiry_rsp.product_id));
      memset(inquiry_rsp.product_rev, ' ', sizeof(inquiry_rsp.product_rev));

      tud_msc_inquiry_cb(lun, inquiry_rsp.vendor_id, inquiry_rsp.product_id, inquiry_rsp.product_rev);

      resplen = sizeof(inquiry_rsp);
      memcpy(buffer, &inquiry_rsp, resplen);
    }
    break;

    case SCSI_CMD_MODE_SENSE_6:
    {
      scsi_mode_sense6_resp_t mode_resp =
      {
          .data_len = 3,
          .medium_type = 0,
          .write_protected = false,
          .reserved = 0,
          .block_descriptor_len = 0  // no block descriptor are included
      };

      bool writable = true;
      if ( tud_msc_is_writable_cb )
      {
        writable = tud_msc_is_writable_cb(lun);
      }

      mode_resp.write_protected = !writable;

      resplen = sizeof(mode_resp);
      memcpy(buffer, &mode_resp, resplen);
    }
    break;

    case SCSI_CMD_REQUEST_SENSE:
    {
      scsi_sense_fixed_resp_t sense_rsp =
      {
          .response_code = 0x70,
          .valid         = 1
      };

      sense_rsp.add_sense_len = sizeof(scsi_sense_fixed_resp_t) - 8;

      sense_rsp.sense_key           = p_msc->sense_key;
      sense_rsp.add_sense_code      = p_msc->add_sense_code;
      sense_rsp.add_sense_qualifier = p_msc->add_sense_qualifier;

      resplen = sizeof(sense_rsp);
      memcpy(buffer, &sense_rsp, resplen);

      // Clear sense data after copy
      tud_msc_set_sense(lun, 0, 0, 0);
    }
    break;

    default: resplen = -1; break;
  }

  return resplen;
}

static void proc_read10_cmd(uint8_t rhport, mscd_interface_t* p_msc)
{
  msc_cbw_t const * p_cbw = &p_msc->cbw;

  // block size already verified not zero
  uint16_t const block_sz = rdwr10_get_blocksize(p_cbw);

  // Adjust lba with transferred bytes
  uint32_t const lba = rdwr10_get_lba(p_cbw->command) + (p_msc->xferred_len / block_sz);

  // remaining bytes capped at class buffer
  int32_t nbytes = (int32_t) tu_min32(sizeof(_mscd_buf), p_cbw->total_bytes-p_msc->xferred_len);

  // Application can consume smaller bytes
  uint32_t const offset = p_msc->xferred_len % block_sz;
  nbytes = tud_msc_read10_cb(p_cbw->lun, lba, offset, _mscd_buf, (uint32_t) nbytes);

  if ( nbytes < 0 )
  {
    // negative means error -> endpoint is stalled & status in CSW set to failed
    TU_LOG(MSC_DEBUG, "  tud_msc_read10_cb() return -1\r\n");

    // Sense = Flash not ready for access
    tud_msc_set_sense(p_cbw->lun, SCSI_SENSE_MEDIUM_ERROR, 0x33, 0x00);

    fail_scsi_op(rhport, p_msc, MSC_CSW_STATUS_FAILED);
  }
  else if ( nbytes == 0 )
  {
    // zero means not ready -> simulate an transfer complete so that this driver callback will fired again
    dcd_event_xfer_complete(rhport, p_msc->ep_in, 0, XFER_RESULT_SUCCESS, false);
  }
  else
  {
    TU_ASSERT( usbd_edpt_xfer(rhport, p_msc->ep_in, _mscd_buf, nbytes), );
  }
}

static void proc_write10_cmd(uint8_t rhport, mscd_interface_t* p_msc)
{
  msc_cbw_t const * p_cbw = &p_msc->cbw;
  bool writable = true;

  if ( tud_msc_is_writable_cb )
  {
    writable = tud_msc_is_writable_cb(p_cbw->lun);
  }

  if ( !writable )
  {
    // Not writable, complete this SCSI op with error
    // Sense = Write protected
    tud_msc_set_sense(p_cbw->lun, SCSI_SENSE_DATA_PROTECT, 0x27, 0x00);
    fail_scsi_op(rhport, p_msc, MSC_CSW_STATUS_FAILED);
    return;
  }

  // remaining bytes capped at class buffer
  int32_t nbytes = (int32_t) tu_min32(sizeof(_mscd_buf), p_cbw->total_bytes-p_msc->xferred_len);

  // Write10 callback will be called later when usb transfer complete
  TU_ASSERT( usbd_edpt_xfer(rhport, p_msc->ep_out, _mscd_buf, nbytes), );
}

// process new data arrived from WRITE10
static void proc_write10_new_data(uint8_t rhport, mscd_interface_t* p_msc, uint32_t xferred_bytes)
{
  msc_cbw_t const * p_cbw = &p_msc->cbw;

  // block size already verified not zero
  uint16_t const block_sz = rdwr10_get_blocksize(p_cbw);

  // Adjust lba with transferred bytes
  uint32_t const lba = rdwr10_get_lba(p_cbw->command) + (p_msc->xferred_len / block_sz);

  // Invoke callback to consume new data
  uint32_t const offset = p_msc->xferred_len % block_sz;
  int32_t nbytes = tud_msc_write10_cb(p_cbw->lun, lba, offset, _mscd_buf, xferred_bytes);

  if ( nbytes < 0 )
  {
    // negative means error -> failed this scsi op
    TU_LOG(MSC_DEBUG, "  tud_msc_write10_cb() return -1\r\n");

    // update actual byte before failed
    p_msc->xferred_len += xferred_bytes;

    // Sense = Flash not ready for access
    tud_msc_set_sense(p_cbw->lun, SCSI_SENSE_MEDIUM_ERROR, 0x33, 0x00);

    fail_scsi_op(rhport, p_msc, MSC_CSW_STATUS_FAILED);
  }else
  {
    // Application consume less than what we got (including zero)
    if ( (uint32_t) nbytes < xferred_bytes )
    {
      if ( nbytes > 0 )
      {
        p_msc->xferred_len += nbytes;
        memmove(_mscd_buf, _mscd_buf+nbytes, xferred_bytes-nbytes);
      }

      // simulate an transfer complete with adjusted parameters --> callback will be invoked with adjusted parameter
      dcd_event_xfer_complete(rhport, p_msc->ep_out, xferred_bytes-nbytes, XFER_RESULT_SUCCESS, false);
    }
    else
    {
      // Application consume all bytes in our buffer
      p_msc->xferred_len += xferred_bytes;

      if ( p_msc->xferred_len >= p_msc->total_len )
      {
        // Data Stage is complete
        p_msc->stage = MSC_STAGE_STATUS;
      }else
      {
        // prepare to receive more data from host
        proc_write10_cmd(rhport, p_msc);
      }
    }
  }
}

#endif