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In the rapidly expanding video surveillance space, customers are demanding higher resolution, more channels and computationally hungry analytics – all at lower cost and power. In this article we explore how HikVision, a leading provider of digital video recorders (DVR), digital video servers (DVS) and surveillance IP modules, has kept pace with these demands with its latest generation products.
Choice of Hardware
In previous generation products, we used a TMS320C6000 DSP from Texas Instruments (TI) paired with an ARM processor. This combination served those products well, but more performance was needed to meet customer demand for more channels and improved image quality.
Many factors were evaluated when choosing a platform for next generation products, such as performance, power consumption, cost and ease of development. ASIC-based solutions offered high performance with the lowest power consumption and per unit cost. However, ASICs presented several problems. One is their (increasingly) high development cost in time and money. To recoup design costs requires prohibitively high volumes. Another problem with ASICs is the lack of flexibility. With their long design cycles, ASICs aren't able to respond effectively to rapidly shifting customer needs.
While FPGAs and massively-parallel processors offer the needed programmability and additional video channels, these devices have their own drawbacks in that these devices can be difficult to program. What was needed was an easy, programmable solution that offered more performance while maintaining low power consumption and a straightforward programming model at a low cost.
Choosing another TI processor was attractive for several reasons – the most obvious being code reuse. HikVision has invested considerable resources implementing highly optimized codecs on the TMS320C64x DSPs. Since TI's next generation DSPs are code compatible with the C64x devices, porting existing code could be done with minimal effort. Another motivation was tools. HikVision's engineers were familiar with TI's Code Composer Studio, which offers a tested development environment and an extensive set of features. And most importantly, TI's roadmap offered a promising way forward with its DaVinci family of digital media processors.
TI's DaVinci portfolio includes fourteen digital media processors based on TI's highest-performance TMS320C64x+ DSP core. The family's flagship devices (see Figure 1), pair a C64x+ DSP core with an ARM9 and a Video Processing Subsystem (VPSS), a host of hardware accelerators for common video processing tasks. Four of the DaVinci members feature this basic configuration. Nine of the DaVinci parts omit the ARM core, featuring just the C64x+ core and VPSS.
Figure 1. High level diagram of TI's TSM320DM644x.
The DaVinci devices were a good fit because they strike a balance between ASICs and programmable DSPs. By offering fixed function (although configurable) accelerators in the VPSS for common video processing tasks such as encoding, decoding and display, the DaVinci devices are able to offer ASIC-like cost and power for the heavy lifting involved in surveillance applications. By offering a high-performance programmable DSP, DaVinci allows designers the flexibility to quickly implement new features like content analytics—a topic we will come back to later in this article.
Because of the wide range of options in the DaVinci family we were able to use DaVinci devices across all product lines (DVR, DVS and IP modules). This enabled a build once, deploy many strategy that greatly lowers engineering development and system cost. Additionally, by integrating the ARM core and hardware accelerators on a single die, the DaVinci parts offered increased performance at a lower cost and power consumption. This higher integration was particularly important in enabling cost and power sensitive products such as the surveillance IP module.
Software
Competition in the video surveillance space is fierce. To compete against ASIC solutions with lower power and cost, HikVision finds its advantage in software. By leveraging the flexibility of software, we can respond more effectively than ASIC designers to customer's specific, shifting needs.
Much of HikVision's R&D budget has gone to video codec development. By developing highly optimized video codecs tailored to video surveillance, we've been able to deliver higher image quality than our competitors while keeping our MIPS budget low. For example, we've developed and patented an H.264 variant that implements H.264 Baseline profile as well as select features of Main profile, including Interlace and B Slice. This "sweet spot" between Baseline and Main profiles offers higher image quality without requiring more expensive hardware or reducing channel density.
Software Challenges
Porting legacy software to DaVinci was not without challenges. Our first challenge was to re-optimize our code to take advantage of new instructions in the C64x+ instruction set. For instance, the C64x+ can perform up to eight 16-bit MAC instructions per cycle. The C62x, in contrast, can only perform two 16-bit MACs per cycle. For MAC intensive audio/video codecs, this represents a large performance boost. The C64x+ also offers new bit-manipulation instructions and expanded add and subtract capabilities. These new instructions, combined with the higher 600 MHz clock rate with the C64x+ (the highest C62x clock rate is 300 MHz) gave our DaVinci based solutions a large performance boost.
We also decided to switch from a proprietary OS (VxWorks) to Open Source Linux. There were several motivations behind the switch. One, of course, is that Linux is royalty free. Another is growing support for Linux OSs on the DaVinci platform. DaVinci processors now support Open Source Linux as well as MontaVista Linux.
The transition to Linux required a significant amount of effort. However, this transition was eased by the Linux support in TI's DSPLink. DSPLink is an interprocessor communication scheme that provides an abstraction layer between the ARM core and DSP. With DSPLink, code running on the ARM uses the same high-level APIs to communicate with the DSP regardless of the OS. These APIs make it easier to switch OSs on the DaVinci platform.
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