stmhal/usbdev: For MSC implement SCSI SYNCHRONIZE_CACHE command.

Currently just a dummy command that returns "success", but it's needed for
some O/S's to correctly talk with the SCSI layer.

stmhal/usbdev/class/inc/usbd_msc_scsi.h

@@ -55,6 +55,8 @@
 #define SCSI_MODE_SENSE6                            0x1A
 #define SCSI_MODE_SENSE10                           0x5A
 #define SCSI_ALLOW_MEDIUM_REMOVAL                   0x1E
+#define SCSI_SYNCHRONIZE_CACHE10                    0x35
+#define SCSI_SYNCHRONIZE_CACHE16                    0x91
 #define SCSI_READ6                                  0x08
 #define SCSI_READ10                                 0x28
 #define SCSI_READ12                                 0xA8

stmhal/usbdev/class/src/usbd_msc_scsi.c

@@ -89,6 +89,7 @@ static int8_t SCSI_StartStopUnit(USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_t
 static int8_t SCSI_AllowMediumRemoval(USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_t *params);
 static int8_t SCSI_ModeSense6 (USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_t *params);
 static int8_t SCSI_ModeSense10 (USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_t *params);
+static int8_t SCSI_SynchronizeCache(USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_t *params);
 static int8_t SCSI_Write10(USBD_HandleTypeDef  *pdev, uint8_t lun , uint8_t *params);
 static int8_t SCSI_Read10(USBD_HandleTypeDef  *pdev, uint8_t lun , uint8_t *params);
 static int8_t SCSI_Verify10(USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_t *params);
@@ -151,6 +152,10 @@ int8_t SCSI_ProcessCmd(USBD_HandleTypeDef  *pdev,
   case SCSI_MODE_SENSE10:
     return SCSI_ModeSense10 (pdev, lun, params);
     
+  case SCSI_SYNCHRONIZE_CACHE10:
+  case SCSI_SYNCHRONIZE_CACHE16:
+    return SCSI_SynchronizeCache(pdev, lun, params);
+
   case SCSI_READ_FORMAT_CAPACITIES:
     return SCSI_ReadFormatCapacity(pdev, lun, params);
     
@@ -374,6 +379,13 @@ static int8_t SCSI_ModeSense10 (USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_t
   return 0;
 }
 
+static int8_t SCSI_SynchronizeCache(USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_t *params) {
+    // nothing to synchronize, so just return "success"
+    USBD_MSC_BOT_HandleTypeDef *hmsc = pdev->pClassData;
+    hmsc->bot_data_length = 0;
+    return 0;
+}
+
 /**
 * @brief  SCSI_RequestSense
 *         Process Request Sense command