introduction
There are many design schemes for video surveillance systems, but the mainstream of market products generally chooses two schemes: one is based on CPU and dedicated video codec ASIC chip. The program chooses to build a CPU and a dedicated media processing chip with ARM as the core. The advantage is that the development time is relatively short, but due to the use of ASIC, the flexibility is poor, and once the product is finalized, it is difficult to change. The second is the use of dedicated DSP for media processing. Its development time is not long. The advantage is that because the algorithm is software code, it can continuously upgrade product performance, and the cost of repeated development is low. TMS320DM642 (hereinafter referred to as DM642), launched by Texas Instruments (TI), the world's largest DSP manufacturer, has been widely accepted and adopted by video application practitioners at home and abroad as a cost-effective DSP dedicated to multimedia applications. This article introduces the main features of DM642 and system application development technology in more detail, and gives video surveillance application examples based on DM642.
DM642 multimedia processor
DM642 is a DSP specially developed by TI for multimedia applications. It uses TI's second-generation advanced super-long instruction word structure (VelociTI), which enables multiple instructions to be processed in parallel in one instruction cycle. It can work at 600MHz clock frequency, and each instruction cycle can parallel 8 32bit instructions, so it can reach the peak calculation speed of 4800MIPS. DM642 uses a two-level cache structure: the first level includes independent LIP (16kB) and LID (16kB), which can only be used as a cache; the second level L2 (256kB) is a unified program / data space, which can be used as a whole SRAM is mapped into storage space, and can also be used as a second-level cache as a whole, or a combination of the two in proportion. DM642 has 64 independent channels of EDMA (Extended Direct Memory Access) controller, responsible for data transmission between on-chip L2 and other peripherals. The large-capacity two-level cache and EDMA channel is one of the high performance of DM642. If it can be reasonably used and managed, it will greatly improve the running performance of the program. Its structure is shown in Figure 1.
In addition, DM642 has rich peripheral device interfaces, including three configurable dual-channel video ports, video ports, each of which is divided into two channels, A and B, and A / B channels can handle one channel of video capture, so DM642 can at most Processing 6-channel video acquisition data (without audio). If the video port is configured for video output, it can only be output on the A channel, but not on the B channel, so the DM642 can support up to 3 video outputs (without audio). If processing audio at the same time, each video port can handle two stereo channels. It also includes 64bit external memory interface (EMIF), 10 / 100Mbit / s Ethernet MAC and multi-channel audio serial port (McASP) and 66MHz32bit PCI interface.
The basic system of DM642 is composed of DM642 and externally expanded memory and peripherals, and the externally expanded memory and peripherals are expanded through the external memory interface (EMIF) of DM642. The external expansion resources necessary for the DM642 basic system include:
(1) SDRAM (4M64bit), used to store programs and cache digital video / audio data;
(2) FLASH (4M8bit), used to store the firmware program for ROM boot;
(3) UART (288bit), extended 2 asynchronous serial ports (RS232 / RS422 / RS485);
(4) On-board register (n × 8bit), composed of several 8-bit status / control registers;
(5) Hard disk interface (2816bit), used for local mass storage interface.
It can be seen from this that DM642 is a powerful multimedia processor that can be used to achieve high-speed digital video / audio codec processing for large amounts of data, and is particularly suitable for the development of multimedia communication equipment. It is an ideal platform for constructing digital multimedia applications.
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