Stretching Multicore For Video Processing

Aug. 11, 2010
The Stretch S7000 series microprocessors target image processing, DVRs and IP cameras with multiple Tensilica Xtensa cores and an ARM 9 microprocessor.

S7 Series

S7100 microprocessor

S7 design flow

Stretch has released its S7000 series multicore microprocessors based on their new S7 configurable processor architecture (Fig. 1). The chips (Fig. 2) target image processing, DVRs and IP cameras. They include hardware support for H.264 encoding.

The S7 architecture (Fig. 3) is based on Tensilica Xtensa microprocessor architecture. The S7 processors also include an Arm ARM 9 microprocessor designed for system management and communication. These new chips deliver 4x performance of the earlier S6000 series while cutting the price per channel by a factor of 4 and reducing the power by a factor of 8. The chips are designed to handle preprocessing and H.264 high profile encoding.

The main Xtensa software configurable processor does most of the heavy lifting sometimes handing off work to the programmable accelerators. The accelerators are also based on the Xtensa architecture but dedicated to specific video processing chores. Stretch's software framework normally hides the inner workings of these processors from the developer. More advanced users might develop image processing software such as gesture recognition and age detection. The latest processors use the same programming model as the prior S6 line. The S7 architecture is more efficient than the S6 and incorporates new features like dual port embedded memory blocks for higher performance processing.

Multichip configurations can be built using high speed serial AIM (Array Interface Matrix) channels found on some of the chips within the family. Each full duplex channel has a 250 Mbyte/s bandwidth. The channel can also act as a PCI Express interface instead. The S7 AIM links only require 4 pins/channel whereas the parallel S6 links required 32 pins/channel. The channels are normally used to pass raw data between Stretch processors. They can eliminate the need for FPGAs or PCI Express bridge chips in a multichip environment thereby reducing the bill of materials (BOM).

The family currently consists of three chips. The high performance S7100 supports 16 channel and can handle 5 Mpixel/s rates at 30 frames/s. It also has 4 AIM/PCI Express channels. The S7110 has 12 channel and can handle 1080p rates at 60 frames/s and it has one AIM/PCI Express channels. The low cost S7120 has 6 channel and can handle 1080p rates at 30 frames/s and is has no AIM/PCI Express channels. The S7120 will find a home in aplications like IP cameras where it can handle everything from auto focus and motorized zoom, image processing to communications, and even provide a flash or USB interface. The chips support booting from secure serial EEPROMs.

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