update msc example

examples/device/nrf52840/src/msc_device_app.c

@@ -97,12 +97,18 @@ int32_t tud_msc_scsi_cb (uint8_t lun, uint8_t const scsi_cmd[16], void* buffer,
     break;
 
     case SCSI_CMD_TEST_UNIT_READY:
-      ptr = NULL;
+      // Command that host uses to check our readiness before sending other commands
       len = 0;
     break;
 
     case SCSI_CMD_PREVENT_ALLOW_MEDIUM_REMOVAL:
-      ptr = NULL;
+      // Host is about to read/write etc ... better not to disconnect disk
+      len = 0;
+    break;
+
+    case SCSI_CMD_START_STOP_UNIT:
+      // Host try to eject/safe remove/powerof us. We could safely disconnect with disk storage, or go into lower power
+      // scsi_start_stop_unit_t const * cmd_start_stop = (scsi_start_stop_unit_t const *) scsi_cmd
       len = 0;
     break;