USB Mass Storage Controller (Flash Drive)

Description

Many products requires a onboard storage memory to store different data like drivers, manuals so that user can access it over the USB connection. The system should be access over a USB host computer. It should mount as a mass storage device (like drive).

To system main parts

NAND Flash Memory: NAND flash memory is a type of non-volatile storage technology that does not require power in order to retain data. The NAND flash memory is of two types,
- NAND Flash (RAW Memory)
  - It is a flash memory without any controller.
  - It can be interface with a microcontroller by writing a driver and firmware for flash operations.
  - It can be interfaced with NAND flash controller chip (Mentioned in point 2).
  - This types of memory are used in the RAM,SSD.
- Managed NAND
  - It is a memory with NAND controller.
  - Example is eMMC/Memory Card, EEPROM IC.
Memory Controller : The NAND Flash controller chip that is dedicatedly designed to control the operations on Raw Flash Memory and Directly Accessible from Windows as a mass storage (Under HID Devices, No need of Driver development). A flash memory controller is the part of solid-state flash memory that communicates with the host device and manages the flash file system directory. The controller is also responsible for wear leveling, error correction and garbage collection.

For the detailed information about the memory interfacing/types, click here.

System Design

OTi2272 chip is used as a flash memory controller. It is a high performance USB 2.0 Mass Storage Class Peripheral controller targeted for applications of USB Flash Disks. The design complies with USB High Speed Specification (480Mb/s).

The controller Integrates the USB 2.0 transceiver with dynamic feedback control, stable slew rate, independent of external loading for reducing EMI. A Phase Lock Loop (PLL) is embedded provides all clocks needed in this controller.

The OTi-2272 accommodates up to 8 Flash devices and works with comprehensive Flash memory technologies available on the market. The controller also has write- protect capability to prevent writing data to Flash.

The controlled can be interfaced with different brands flash memory like Hynix, Sandisk, Samsung. Each memory controller has its own list of supported NAND flash memory depending on the flash type MLC/TLC and its density. This list is provided by the flash memory controller vendor. Below is the list example.

In this system, A 2GB (8Gbit) NAND flash memory (Hynix H27UAG8T2ATR) is interfaced with the OTI2272 controller.

The memory can be mounted in two mode.

Mass Storage: In this mode, the memory mount as a removable flash drive. Like a normal flash drive. In Read/write mode.
CD Drive : In this mode, the memory mount in readonly mode like the CD. User can not delete the data from the drive.

The memory is configured using the Windows utility provided by Oti.

Customized Firmware

Vendor provided another utiltiy to lock/unlock the flash drive in mass storage mode. When the drive is unlocked it goes into writable mode. User can copy the files in the drive. This mode is used to copy the files like driver at the time of assembly the product. Once the files are copied, the drive is set into lock mode and user can not format drive or delete the data.

Utility Uses

The utilty is used for the below purpose

Change the VID/PID (If required)
Change the Product and Vendor String
- Product String is the name that will be displayed in the Windows device manager.
Fix the flash memory usable capacity.
- It use to set the memory size less than its actual capacity.

Below is the screenshot of USB Drive mounted in windows explorer after plugging the device. Changed product string to “Nikhil Test Flash drive”.

OTi2272 datasheet

List of Other Flash Memory Controller used for Testing

CBM1180 USB2.0 Controller
SM3257 USB2.0 Controller
IS917 USB3.0 Controller

Test PCBA

The test PCB is divided into two parts

One PCB has OTi Controller, USB connector and other components.
Another PCB has NAND flash memory. This PCB plugs into the controller PCB. It it designed to test different NAND flash memories.