The overall design scheme of HD IPTV set-top box based on STB7100

Tag: STB7100 IPTV

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IPTV uses computers or set-top boxes + TVs as receiving terminals. The completed services include live TV, video on demand, time-shifted TV, web browsing, information services, interactive games, and future scalable services [1]. With the increase of broadband users, broadband streaming media services based on video services have become important services in broadband value-added services. At the same time, the demand for high-quality, high-definition audio and video services has made HD development an inevitable trend. Therefore, the combination of HD and IVI'V will become one of the hottest broadband value-added applications with the most potential and most profitable prospects on the current broadband network.

2 IPTV set-top box overall design

According to the functions of the high-definition IPTV set-top box, comprehensively examine the solutions of several major IPTV chip manufacturers such as ST and Broadcom, as well as the current market conditions. The author selects ST's STB7100 chip for design [2]. The product is the world's first single-chip solution supporting H.264/AVC and MPEG-2 HD standards, and integrates all the features required for high-performance multi-standard video decoding circuits and set-top boxes. The STB7100 chip is a cost-effective product in the sTB710x series. It integrates all the functions of STB and multi-standard decoding circuits on a single chip. It can simultaneously decode multiple HD video streams and output the synthesized video to 2 TVs. Machine, or display it in the form of picture-in-picture. The STB7100 chip provides a complete solution. The embedded operating system can be used in any of Linux, OS21 and WinCE, providing a greater choice for upper-level software development.

3 IPTV set-top box hardware structure design

According to the system requirements, the overall framework of the hardware structure is developed. As shown in Figure 1, a dedicated set-top box decoder chip is selected as the main control CPU, and the peripheral circuits of the CPU and the necessary functional circuits are designed [3]. Local Memory Interface (LMI) 32-bit DDR memory for system operation and audio and video data storage; External Memory Interface (EMI) provides support for a variety of peripherals, including Flash, ROM And network cards, etc. The network port module is used to complete the function of receiving and processing IP data and audio and video streams; the audio and video output module performs the output function of the audio and video signals; the power module is responsible for the power supply of the chip and the whole system; and the external interface completes the signal of the CPU to each functional module. Control function for transmission.

Figure 1 hardware system block diagram

3.1 set-top box core processing chip STB7100

The sTB7100 is a high-performance, single-chip integrated audio and video decoding media processor. The main modules are:

1) processor core device

The high-performance ST40 with a frequency of 266 MHz is the CPU core of the device. It belongs to ST's 32-bit RISC series and uses SuperH architecture to control other parts of the chip, including communication with two ST231 CPUs. In addition, there are two ST231 CPUs with a frequency of 400 MHz for processing audio and video.

2) Video decoding module and interface

The sTB7100 supports multiple video decoding standards, including H.264/AVC and MPEG-2 bidirectional decoding standards. The resolution is up to 1 920 × 1 080i or l 920 × 720p. At the same time, the STB7100 has multiple video interfaces such as D1 standard definition input, RGB/YPbPr/YC/CBS analog HD and SD output, and integrated high-bandwidth digital media interface (HDMI) and high-definition content copy protection interface (HDCP).

3) Audio decoding module and interface

A 400 MHz ST231 CPU is used as the decoder and is compatible with all common audio standards. The audio stream input can be a PCM digital input in the I2S format or an internal source input through the memory transfer subsystem. The output interface includes S/PDIF serial digital audio output and 24-bit stereo analog output.

4) Other peripheral interfaces

The STB7100 offers a wide range of peripheral interfaces to choose from, including a UART interface, an infrared interface, a SmartCard interface, and a Serial ATA (SATA) hard drive interface and a USB 2.0 host controller port.

3.2 Local Memory Interface Module (LMI)

In order to meet the requirements of different types of video, there must be enough memory space for storing and decoding video and audio streams. LMI selects 64 Mbyte of memory for H.264 decoding or MPEG-2 bidirectional decoding. The connection method is shown in Figure 2.

Among them, the internal block addressing of DDR is determined by BAO and BAl, and 4 memory blocks can be addressed, that is, there are 4 banks in one memory chip. A0-A12 is used to address the row address in the block, and AO~A8 are used to address the column address in the block, so the capacity of each chip is 32 Mbyte. Since the bit width of each memory chip is 16 bits, and the data bit width of the CPU is 32 bits, in order to work in cooperation with the CPU, it is necessary to transmit a data amount consistent with the CPI.I bus bit width, so two memory chips are required to A 32-bit data width is reached. Two 32 Mbyte memory chips work simultaneously, using the same chip select signal CS control, and also use the same BA0 and BAl signals to control Bank selection.

Figure 2 DDR SDRAM connection schematic

3.3 External Memory Interface Module (EMI)

EMI is an external memory interface used by the ST chip to support general purpose. It is divided into 5 banks, allowing the system to support various types of memory, external processor interfaces and other devices, accessing 5 different types of signals through 5 different chip select signals. equipment. Two types of devices, FLASh{ and NIC, are available in the system. The following two devices are introduced separately:

1) FLASH is a device for storing U-boot boot code, kernel and file system. Its first address defaults to the starting address when the system is powered on. FLASH uses ST's M58LW064D, which is a 64Mbyte FLASH memory with a 0.15μm NOR process and a single 2.7 to 3.6 V supply. The memory is divided into 64 blocks that can be individually erased, 1 Mbyte each. The program and erase commands are written into the memory through the interface. In actual applications, the FLASH is written, erased, and protected by the cp, erase, and protect commands under U-boot; the state memory provides status information for various operations. The memory write buffer allows the processor to program l~16 bytes in parallel. In order to be able to program and erase other blocks, the block being programmed can be suspended and then restored; the block hold function prevents the protected block from being programmed and erased. At power-up, all blocks are protected and block protection commands can be used to protect or abort certain blocks. When programming, erasing can make Vpen low, then all programming and erasing is prevented. The STS signal can be set to both ready/busy (RY/BY) modes, with the high level ready and the low level busy, set high here, always ready. 2) After comprehensive consideration of various factors such as function and price, DAVICOM's cost-effective DM9000AE Fast Ethernet control processor is used as the network interface. The circuit schematic is shown in Figure 3. Among them, the network transformer uses PM34-1006M of PPT Company. It does not support AUTO MDIX itself, so CTp0 and CTsl, CTsO and CTpl need to be connected.

Figure 3 network interface circuit diagram

4 IPTV set-top box software structure design

Considering cost and versatility, the set-top box uses the Linux operating system. The embedded operating system is responsible for the allocation and scheduling of all software and hardware resources of the set-top box system, controlling and coordinating concurrent activities, and can achieve the functions required by the system by loading and unloading certain modules. Figure 4 shows the software structure of the system, with the Linux operating system as the core, downwards through the various drivers for the hardware system, provisioning various hardware resources, upward loading of audio and video related applications and applications for other tasks [ 4].

Figure 4 IPTV software basic structure

The set-top box can be divided into three layers: the operating system is mainly used to complete the operation of the hardware device, and provides support for the upper layer; the API layer is supported, and the application program is translated into an instruction that the CPU can recognize, and the hardware device is called to complete the corresponding operation; The top layer mainly implements media playback, browsers, and applications such as EPG, which are directly operated by the user.

Figure 5 shows the basic structure of the Linux network driver. When sending data, the application layer data is sent to the lower layer through dev_queue_xmit( ), and dev_queue_xmit( ) sends data to the device through the network device interface hard_star_xmit( ) function pointer, and sends the data of the application layer to Hardware device; when receiving data, when the network data arrives at the device, an interrupt is generated, the interrupt processing subroutine is entered, and then the accept function is called to accept the data, and then sent to the upper layer through the netif_ix() function. When writing the DM9000AE driver, in addition to functions such as detection, transmission acceptance, and interrupt, it also corresponds to the open board. Pay attention to the base address and interrupt of the network card. Since the address line and data line of the DM9000AE are multiplexed, the relationship between the I/O port address line and the data line for reading data is determined according to the circuit schematic.

Figure 5 Linux network driver structure

Based on the realization of the network function, this design uses the NFS protocol to implement the network mount file system, and writes the boot loader and the kernel image to the FLASH, so that the application can be directly placed in the file system of the PC, saving the set-top box. Memory space. At present, the hardware circuit design has been completed. After testing, it can play H.264 and MPEG-2 HD and SD video streams, and can play audio content in MPEG-1, AAC, PCM and other formats. In addition, the GTK-based Dillo browser is adopted. Since it does not support .1 avaScript, Java and other additional functions, it has the advantages of small size and fast speed. Various function modules such as video modules and EPG modules can be used as plug-ins with the Dillo browser. When an interactive service is required, the EPG server can be accessed through the HTTP protocol to obtain EPG related information, and the EPG can be parsed and reconstructed locally. If you need to order the video, you can go to the video server to get the URL of the video source, then parse the URL and send it to the video function module for decoding.

5 Summary

The basic components of the IPTV set-top box hardware circuit are introduced, and the system solution with STB7100 as the core is determined. The STB7100 has powerful audio and video processing capabilities, and can be extended by function chips through its rich peripheral interface to achieve various functions required. Although the author has realized some functions, the design of the set-top box still needs to be improved, and further research on the extended functions such as smart card and digital copyright management is needed.

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