refactor async io, add in_isr argument to tud_msc_async_io_done()

use cbw.command[0] for pending IO command

2 files changed, 122 insertions, 157 deletions

diff --git a/src/class/msc/msc_device.c b/src/class/msc/msc_device.c
index e583f6ba8..709734b87 100644
--- a/src/class/msc/msc_device.c
+++ b/src/class/msc/msc_device.c
@@ -52,36 +52,27 @@ enum {
   MSC_STAGE_NEED_RESET,
 };
 
-enum {
-  MSC_NEXT_OP_NONE = 0,
-  MSC_NEXT_OP_READ10,
-  MSC_NEXT_OP_WRITE10,
-  MSC_NEXT_OP_STATUS
-};
-
 typedef struct {
-  TU_ATTR_ALIGNED(4) msc_cbw_t cbw;
-  TU_ATTR_ALIGNED(4) msc_csw_t csw;
-
+  TU_ATTR_ALIGNED(4) msc_cbw_t cbw; // 31 bytes
   uint8_t  rhport;
+
+  TU_ATTR_ALIGNED(4) msc_csw_t csw; // 13 bytes
   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
+  // Bulk Only Transfer (BOT) Protocol
+  uint8_t stage;
+
+  // SCSI Sense Response Data
   uint8_t sense_key;
   uint8_t add_sense_code;
   uint8_t add_sense_qualifier;
 
-  // Async IO
-  uint8_t next_op;
-  uint32_t xferred_bytes;
+  uint8_t pending_io; // pending async IO
 }mscd_interface_t;
 
 static mscd_interface_t _mscd_itf;
@@ -95,12 +86,11 @@ CFG_TUD_MEM_SECTION static struct {
 //--------------------------------------------------------------------+
 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(mscd_interface_t* p_msc);
-static void proc_read10_next(mscd_interface_t* p_msc, int32_t nbytes);
+static void proc_read_io_data(mscd_interface_t* p_msc, int32_t nbytes);
 static void proc_write10_cmd(mscd_interface_t* p_msc);
-static void proc_write10_new_data(mscd_interface_t* p_msc, uint32_t xferred_bytes);
-static void proc_write10_next(mscd_interface_t* p_msc, uint32_t xferred_bytes, int32_t nbytes);
+static void proc_write10_host_data(mscd_interface_t* p_msc, uint32_t xferred_bytes);
+static void proc_write_io_data(mscd_interface_t* p_msc, uint32_t xferred_bytes, int32_t nbytes);
 static bool proc_stage_status(mscd_interface_t* p_msc);
-static void tud_msc_async_io_done_cb(void* bytes_processed);
 
 TU_ATTR_ALWAYS_INLINE static inline bool is_data_in(uint8_t dir) {
   return tu_bit_test(dir, 7);
@@ -195,30 +185,31 @@ static uint8_t rdwr10_validate_cmd(msc_cbw_t const* cbw) {
   return status;
 }
 
-static bool proc_stage_status(mscd_interface_t* p_msc) {
+static bool proc_stage_status(mscd_interface_t *p_msc) {
   uint8_t rhport = p_msc->rhport;
-  msc_cbw_t const* p_cbw = &p_msc->cbw;
+  msc_cbw_t const *p_cbw = &p_msc->cbw;
+
   // 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_DRV("  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(p_msc));
-      }
+  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_DRV("  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(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(p_msc);
-    }
-    #endif
-    return true;
+  #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(p_msc);
+  }
+  #endif
+  return true;
 }
 
 //--------------------------------------------------------------------+
@@ -258,39 +249,57 @@ bool tud_msc_set_sense(uint8_t lun, uint8_t sense_key, uint8_t add_sense_code, u
   return true;
 }
 
-static inline void set_sense_medium_not_present(uint8_t lun) {
+TU_ATTR_ALWAYS_INLINE static inline void set_sense_medium_not_present(uint8_t lun) {
   // default sense is NOT READY, MEDIUM NOT PRESENT
   tud_msc_set_sense(lun, SCSI_SENSE_NOT_READY, 0x3A, 0x00);
 }
 
-void tud_msc_async_io_done(int32_t bytes_processed) {
-  // Precheck to avoid queueing multiple RW done callback
-  TU_VERIFY(_mscd_itf.next_op != MSC_NEXT_OP_NONE,);
-  // Call usbd_edpt_xfer() in tud_task() to avoid racing condition
-  usbd_defer_func(tud_msc_async_io_done_cb, (void*) (intptr_t)bytes_processed, false);
+static void proc_async_io_done(void *bytes_processed) {
+  mscd_interface_t *p_msc = &_mscd_itf;
+  TU_VERIFY(p_msc->pending_io, );
+  const int32_t nbytes = (int32_t) (intptr_t) bytes_processed;
+  const uint8_t cmd = p_msc->cbw.command[0];
+
+  p_msc->pending_io = 0;
+  switch (cmd) {
+    case SCSI_CMD_READ_10:
+      proc_read_io_data(p_msc, nbytes);
+      break;
+
+    case SCSI_CMD_WRITE_10:
+      proc_write_io_data(p_msc, (uint32_t) nbytes, nbytes);
+      break;
+
+    default: break;
+  }
+
+  // send status if stage is transitioned to STATUS
+  if (p_msc->stage == MSC_STAGE_STATUS) {
+    proc_stage_status(p_msc);
+  }
 }
 
-static void tud_msc_async_io_done_cb(void* bytes_processed) {
-  TU_VERIFY(_mscd_itf.next_op != MSC_NEXT_OP_NONE,);
-  uint8_t next_op = _mscd_itf.next_op;
-  _mscd_itf.next_op = MSC_NEXT_OP_NONE;
-  int32_t nbytes = (int32_t)(intptr_t)bytes_processed;
-  // READ10
-  if (next_op == MSC_NEXT_OP_READ10) {
-    proc_read10_next(&_mscd_itf, nbytes);
-  } else if (next_op == MSC_NEXT_OP_WRITE10) {
-    proc_write10_next(&_mscd_itf, _mscd_itf.xferred_bytes, nbytes);
-    // Need to manually invoke CSW transfer
-    if (_mscd_itf.stage == MSC_STAGE_STATUS) {
-      proc_stage_status(&_mscd_itf);
-    }
+bool tud_msc_async_io_done(int32_t bytes_io, bool in_isr) {
+  // Precheck to avoid queueing multiple RW done callback
+  TU_VERIFY(_mscd_itf.pending_io);
+  if (bytes_io == 0) {
+    bytes_io = TUD_MSC_RET_ERROR; // 0 is treated as error, no sense to call this with BUSY here
+  }
+
+  if (in_isr) {
+    usbd_defer_func(proc_async_io_done, (void*) (intptr_t)bytes_io, in_isr);
+  } else {
+    proc_async_io_done((void*)(intptr_t) bytes_io);
   }
+
+  return true;
 }
 
 //--------------------------------------------------------------------+
 // USBD Driver API
 //--------------------------------------------------------------------+
 void mscd_init(void) {
+  TU_LOG_INT(CFG_TUD_MSC_LOG_LEVEL, sizeof(mscd_interface_t));
   tu_memclr(&_mscd_itf, sizeof(mscd_interface_t));
 }
 
@@ -528,7 +537,7 @@ bool mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t
           proc_read10_cmd(p_msc);
         }
       } else if (SCSI_CMD_WRITE_10 == p_cbw->command[0]) {
-        proc_write10_new_data(p_msc, xferred_bytes);
+        proc_write10_host_data(p_msc, xferred_bytes);
       } else {
         p_msc->xferred_len += xferred_bytes;
 
@@ -560,7 +569,7 @@ bool mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t
     break;
 
     case MSC_STAGE_STATUS_SENT:
-      // Wait for the Status phase to complete
+      // Status phase is complete
       if ((ep_addr == p_msc->ep_in) && (xferred_bytes == sizeof(msc_csw_t))) {
         TU_LOG_DRV("  SCSI Status [Lun%u] = %u\r\n", p_cbw->lun, p_csw->status);
         // TU_LOG_MEM(CFG_TUD_MSC_LOG_LEVEL, p_csw, xferred_bytes, 2);
@@ -590,7 +599,7 @@ bool mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t
 
         TU_ASSERT(prepare_cbw(p_msc));
       } else {
-        // Any xfer ended here is consider unknown error, ignore it
+        // Any xfer ended here is considered unknown error, ignore it
         TU_LOG1("  Warning expect SCSI Status but received unknown data\r\n");
       }
       break;
@@ -696,8 +705,7 @@ static int32_t proc_builtin_scsi(uint8_t lun, uint8_t const scsi_cmd[16], uint8_
     break;
 
     case SCSI_CMD_READ_FORMAT_CAPACITY: {
-      scsi_read_format_capacity_data_t read_fmt_capa =
-      {
+      scsi_read_format_capacity_data_t read_fmt_capa = {
         .list_length = 8,
         .block_num = 0,
         .descriptor_type = 2, // formatted media
@@ -729,8 +737,7 @@ static int32_t proc_builtin_scsi(uint8_t lun, uint8_t const scsi_cmd[16], uint8_
     break;
 
     case SCSI_CMD_INQUIRY: {
-      scsi_inquiry_resp_t inquiry_rsp =
-      {
+      scsi_inquiry_resp_t inquiry_rsp = {
         .is_removable = 1,
         .version = 2,
         .response_data_format = 2,
@@ -750,8 +757,7 @@ static int32_t proc_builtin_scsi(uint8_t lun, uint8_t const scsi_cmd[16], uint8_
     break;
 
     case SCSI_CMD_MODE_SENSE_6: {
-      scsi_mode_sense6_resp_t mode_resp =
-      {
+      scsi_mode_sense6_resp_t mode_resp = {
         .data_len = 3,
         .medium_type = 0,
         .write_protected = false,
@@ -772,8 +778,7 @@ static int32_t proc_builtin_scsi(uint8_t lun, uint8_t const scsi_cmd[16], uint8_
     break;
 
     case SCSI_CMD_REQUEST_SENSE: {
-      scsi_sense_fixed_resp_t sense_rsp =
-      {
+      scsi_sense_fixed_resp_t sense_rsp = {
         .response_code = 0x70, // current, fixed format
         .valid = 1
       };
@@ -805,32 +810,27 @@ static int32_t proc_builtin_scsi(uint8_t lun, uint8_t const scsi_cmd[16], uint8_
 
 static void proc_read10_cmd(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
+  uint16_t const block_sz = rdwr10_get_blocksize(p_cbw); // already verified non-zero
+  // Adjust lba & offset with transferred bytes
   uint32_t const lba = rdwr10_get_lba(p_cbw->command) + (p_msc->xferred_len / block_sz);
+  uint32_t const offset = p_msc->xferred_len % block_sz;
 
   // remaining bytes capped at class buffer
   int32_t nbytes = (int32_t)tu_min32(CFG_TUD_MSC_EP_BUFSIZE, p_cbw->total_bytes - p_msc->xferred_len);
 
-  // Application can consume smaller bytes
-  uint32_t const offset = p_msc->xferred_len % block_sz;
-
-  p_msc->next_op = MSC_NEXT_OP_READ10;
+  p_msc->pending_io = 1;
   nbytes = tud_msc_read10_cb(p_cbw->lun, lba, offset, _mscd_epbuf.buf, (uint32_t)nbytes);
   if (nbytes != TUD_MSC_RET_ASYNC) {
-    p_msc->next_op = MSC_NEXT_OP_NONE;
-    proc_read10_next(p_msc, nbytes);
+    p_msc->pending_io = 0;
+    proc_read_io_data(p_msc, nbytes);
   }
 }
 
-static void proc_read10_next(mscd_interface_t* p_msc, int32_t nbytes) {
+static void proc_read_io_data(mscd_interface_t* p_msc, int32_t nbytes) {
   uint8_t rhport = p_msc->rhport;
   if (nbytes < 0) {
     // negative means error -> endpoint is stalled & status in CSW set to failed
-    TU_LOG_DRV("  tud_msc_read10_cb() return -1\r\n");
+    TU_LOG_DRV("  IO read() failed\r\n");
 
     // set sense
     msc_cbw_t const* p_cbw = &p_msc->cbw;
@@ -838,7 +838,7 @@ static void proc_read10_next(mscd_interface_t* p_msc, int32_t nbytes) {
 
     fail_scsi_op(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
+    // zero means not ready -> fake a transfer complete so that this driver callback will fire 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_epbuf.buf, (uint16_t) nbytes),);
@@ -864,55 +864,42 @@ static void proc_write10_cmd(mscd_interface_t* p_msc) {
   // remaining bytes capped at class buffer
   uint16_t nbytes = (uint16_t)tu_min32(CFG_TUD_MSC_EP_BUFSIZE, p_cbw->total_bytes - p_msc->xferred_len);
   // Write10 callback will be called later when usb transfer complete
-  uint8_t rhport = p_msc->rhport;
-  TU_ASSERT(usbd_edpt_xfer(rhport, p_msc->ep_out, _mscd_epbuf.buf, nbytes),);
+  TU_ASSERT(usbd_edpt_xfer(p_msc->rhport, p_msc->ep_out, _mscd_epbuf.buf, nbytes),);
 }
 
 // process new data arrived from WRITE10
-static void proc_write10_new_data(mscd_interface_t* p_msc, uint32_t xferred_bytes) {
+static void proc_write10_host_data(mscd_interface_t* p_msc, uint32_t xferred_bytes) {
   msc_cbw_t const* p_cbw = &p_msc->cbw;
+  uint16_t const block_sz = rdwr10_get_blocksize(p_cbw); // already verified non-zero
 
-  // block size already verified not zero
-  uint16_t const block_sz = rdwr10_get_blocksize(p_cbw);
-
-  // Adjust lba with transferred bytes
+  // Adjust lba & offset 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;
 
-  p_msc->next_op = MSC_NEXT_OP_WRITE10;
-  p_msc->xferred_bytes = xferred_bytes;
+  p_msc->pending_io = 1;
   int32_t nbytes =  tud_msc_write10_cb(p_cbw->lun, lba, offset, _mscd_epbuf.buf, xferred_bytes);
   if (nbytes != TUD_MSC_RET_ASYNC) {
-    p_msc->next_op = MSC_NEXT_OP_NONE;
-    proc_write10_next(p_msc, xferred_bytes, nbytes);
+    p_msc->pending_io = 0;
+    proc_write_io_data(p_msc, xferred_bytes, nbytes);
   }
 }
 
-static void proc_write10_next(mscd_interface_t* p_msc, uint32_t xferred_bytes, int32_t nbytes) {
+static void proc_write_io_data(mscd_interface_t* p_msc, uint32_t xferred_bytes, int32_t nbytes) {
   if (nbytes < 0) {
     // negative means error -> failed this scsi op
-    TU_LOG_DRV("  tud_msc_write10_cb() return -1\r\n");
-
-    // update actual byte before failed
-    p_msc->xferred_len += xferred_bytes;
-
-    msc_cbw_t const* p_cbw = &p_msc->cbw;
-    set_sense_medium_not_present(p_cbw->lun);
+    TU_LOG_DRV("  IO write() failed\r\n");
+    set_sense_medium_not_present(p_msc->cbw.lun);
     fail_scsi_op(p_msc, MSC_CSW_STATUS_FAILED);
   } else {
     if ((uint32_t)nbytes < xferred_bytes) {
       // Application consume less than what we got (including zero)
       const uint32_t left_over = xferred_bytes - (uint32_t)nbytes;
       if (nbytes > 0) {
-        p_msc->xferred_len += (uint16_t)nbytes;
         memmove(_mscd_epbuf.buf, _mscd_epbuf.buf + nbytes, left_over);
       }
 
-      // simulate a transfer complete with adjusted parameters --> callback will be invoked with adjusted parameter
-      uint8_t rhport = p_msc->rhport;
-      dcd_event_xfer_complete(rhport, p_msc->ep_out, left_over, XFER_RESULT_SUCCESS, false);
+      // fake a transfer complete with adjusted parameters --> callback will be invoked with adjusted parameters
+      dcd_event_xfer_complete(p_msc->rhport, p_msc->ep_out, left_over, XFER_RESULT_SUCCESS, false);
     } else {
       // Application consume all bytes in our buffer
       p_msc->xferred_len += xferred_bytes;
diff --git a/src/class/msc/msc_device.h b/src/class/msc/msc_device.h
index 7162b11e4..2ad31c245 100644
--- a/src/class/msc/msc_device.h
+++ b/src/class/msc/msc_device.h
@@ -49,10 +49,11 @@
 #endif
 
 // Return value of callback functions
-// Error
-#define TUD_MSC_RET_ERROR  -1
-// Asynchronous IO
-#define TUD_MSC_RET_ASYNC  -16
+enum {
+  TUD_MSC_RET_BUSY = 0,   // Busy, e.g disk I/O is not ready
+  TUD_MSC_RET_ERROR = -1,
+  TUD_MSC_RET_ASYNC = -2, // Asynchronous IO
+};
 
 TU_VERIFY_STATIC(CFG_TUD_MSC_EP_BUFSIZE < UINT16_MAX, "Size is not correct");
 
@@ -63,54 +64,31 @@ TU_VERIFY_STATIC(CFG_TUD_MSC_EP_BUFSIZE < UINT16_MAX, "Size is not correct");
 // Set SCSI sense response
 bool tud_msc_set_sense(uint8_t lun, uint8_t sense_key, uint8_t add_sense_code, uint8_t add_sense_qualifier);
 
-// Called once asynchronous read/write operation is done
-// bytes_processed has the same meaning of tud_msc_read10_cb() /
-// tud_msc_write10_cb() return value
-void tud_msc_async_io_done(int32_t bytes_processed);
+// Called by Application once asynchronous I/O operation is done
+// bytes_io is number of bytes in I/O op, typically the bufsize in read/write_cb() or
+// TUD_MSC_RET_ERROR (-1) for error. Note TUD_MSC_RET_BUSY (0) will be treated as error as well.
+bool tud_msc_async_io_done(int32_t bytes_io, bool in_isr);
 
 //--------------------------------------------------------------------+
 // Application Callbacks (WEAK is optional)
 //--------------------------------------------------------------------+
 
-// Invoked when received SCSI READ10 command
-// - Address = lba * BLOCK_SIZE + offset
-//   - offset is only needed if CFG_TUD_MSC_EP_BUFSIZE is smaller than BLOCK_SIZE.
-//
-// - Application fill the buffer (up to bufsize) with address contents and return number of bytes read or status.
-//
-//   - ret < bufsize  : These bytes are transferred first and callback will be invoked again for remaining data.
-//
-//   - ret == 0       : Indicate application is not ready yet e.g disk I/O busy.
-//                      Callback will be invoked again with the same parameters later on.
-//
-//   - ret == TUD_MSC_RET_ERROR (-1)
-//                    : Indicate application error e.g invalid address. This request will be STALLed
-//                      and return failed status in command status wrapper phase.
-//
-//   - ret == TUD_MSC_RET_ASYNC (-16)
-//                    : Data reading will be done asynchronously in a background task. Application should return immediately.
-//                      tud_msc_async_io_done() must be called once reading is done to signal completion.
+/*
+  Invoked when received SCSI READ10/WRITE10 command
+  - Address = lba * BLOCK_SIZE + offset
+    - offset is only needed if CFG_TUD_MSC_EP_BUFSIZE is smaller than BLOCK_SIZE.
+  - Application fill the buffer (up to bufsize) with address contents and return number of bytes read or status.
+    - 0 < ret < bufsize: These bytes are transferred first and callback will be invoked again for remaining data.
+    - ret == TUD_MSC_RET_BUSY
+        Application is buys e.g disk I/O not ready.
+        Callback will be invoked again with the same parameters later on.
+    - ret == TUD_MSC_RET_ERROR
+        error such as invalid address. This request will be STALLed and scsi command will be failed
+    - ret == TUD_MSC_RET_ASYNC
+        Data I/O will be done asynchronously in a background task. Application should return immediately.
+        tud_msc_async_io_done() must be called once IO/ is done to signal completion.
+*/
 int32_t tud_msc_read10_cb (uint8_t lun, uint32_t lba, uint32_t offset, void* buffer, uint32_t bufsize);
-
-// Invoked when received SCSI WRITE10 command
-// - Address = lba * BLOCK_SIZE + offset
-//   - offset is only needed if CFG_TUD_MSC_EP_BUFSIZE is smaller than BLOCK_SIZE.
-//
-// - Application writes data from buffer to address contents (up to bufsize) and returns the number of bytes written or status.
-//
-//   - ret < bufsize  : Callback will be invoked again with remaining data later on.
-//
-//   - ret == 0       : Indicate application is not ready yet e.g disk I/O busy.
-//                      Callback will be invoked again with the same parameters later on.
-//
-//   - ret == TUD_MSC_RET_ERROR (-1)
-//                    : Indicate application error e.g invalid address. This request will be STALLed
-//                      and return failed status in command status wrapper phase.
-//
-//   - ret == TUD_MSC_RET_ASYNC (-16)
-//                    : Data writing will be done asynchronously in a background task. Application should return immediately.
-//                      tud_msc_async_io_done() must be called once writing is done to signal completion.
-// TODO change buffer to const uint8_t*
 int32_t tud_msc_write10_cb (uint8_t lun, uint32_t lba, uint32_t offset, uint8_t* buffer, uint32_t bufsize);
 
 // Invoked when received SCSI_CMD_INQUIRY