Posedge SSD Controller Sub-System

With the NAND Flash prices following Moore’s law, they offer significant long-term benefits over the conventional HDD drives. And the SSD based Flash drives are expected to replace traditional HDD drives in PCs, Servers and also embedded applications. HDDs are already replaced with high-density MLC/SLC flash devices in MP3/Video players and PDA’s. However Flash devices do pose new problems with respect to endurance and bad block management.
The Flash performance and power dissipation advantages out-weight the disadvantages and the SSD controllers help overcome the shortcomings.
Conventional Flash Controller IP’s just provide an interface to the flash or in some cases provide ECC logic along with the Flash Interface. However, the requirements for the next generation flash controllers are

• ECC up to 64 bit correction
• Wear-Leveling Table for endurance
• Automatic Chaining of Good/Bad Blocks
• Buffer Management for optimal accesses

Currently, these problems are solved with dedicated high performance controllers (expensive for embedded systems) or by Host software. These options are sub-optimal because of higher power and higher cost involved in using them.

Posedge SSD Solution

Posedge’s ONFI2.2 compliant Flash Controllers are integrated with other Posedge SSD functional blocks to perform Error Correction, bad block management, File System support and Wear-Leveling. The flash controller interfaces to multiple Flash devices.

Flash Specifications

Posedge Flash Controller has the following specifications

• ONFI2.2 Compliant
• Synchronous and Asynchronous Mode
• 200 MHz Interface Clock
• Toggle Mode
• Multiple Flash Channels

SSD Controller Sub-System supports multiple Flash devices (upto 16 devices) using single or multiple Flash Controller state machines.

ECC Support

The SSD Controller Sub-System can correct errors up to 64-bits per block of data. The ECC data is stored in the spare area of the NAND Flash and updated for writes automatically and checked for reads. Posedge ECC implements BCH encoding and decoding for optimal performance and the level of Error Correction is configurable depending on the area / performance requirement.

Boot Support

Posedge Flash System supports boot mode of operation. In boot mode, the NAND Flash is accessed with default configuration, without any initialization from the host processor. The boot state-machine initializes the Flash devices (RESET CMD etc.) and directly accesses the Flash Memory without page programming etc.

Wear Leveling

 The SSD Controller Sub-System has hardware maintained translations tables for translating the virtual addresses to physical addresses. The SSD Controller Sub-System creates the dynamic translation tables based on their usage for maximum endurance without loss of performance over time.

Bad Block Management

Flash Memory by design will have bad blocks that are unusable for storage. The usable blocks are chained together and the hardware maintains the linked list.

Complementary Technologies

Posedge has a strong IP portfolio augmenting the SSD Controllers to enable multiple market segments. The field proven crypto and compression engines can be integrated in the SSD Controller Sub-System for security and better throughputs.

Posedge has a very area efficient AES-128 bit core (XTS Mode) as part of its crypto library and AES-XTS is the most prevalent encryption algorithm in Non-Volatile storage to protect content against theft.

In addition Posedge’s PZLIB library of cores provide standards based compression ratios of 3:1 for better packing of data and to achieve more throughput than conventional SSD Controllers.

Applications

Posedge SSD Controller Sub-System IP is suited to various applications interfacing to NAND Flash for storage. The solution increases the overall efficiency of the Flash accesses, reduces the power consumption and hence suitable for mobile computing devices.

• Set-Top Boxes          
• Currently Hard-disk based
• Conversion is just starting
• Performance to match Video Traffic
• Mobile Devices (Cell Phones / PDAs)
• Low Power
• Reduce the Processor Overhead
• Embedded Storage
• Multi-Flash Controller
• HDD replacement

Performance Advantage

Posedge SSD solution has best read/write performance for the area.

Sustained performance of 45 Mbytes/sec.
• Read Performance of 50 Mbytes/sec
• Write Performance of 50 Mbytes/sec
• Higher Performance with compression (150 Mbytes/sec)
• Low Power Solution