Design of Internet Broadcasting Based on ARM 926EJ-S Microcontroller

This paper proposes a network broadcast design scheme for embedded systems based on ARM and PoE. The scheme uses the ARM926EJ-S processor and its peripheral modules as the hardware platform and embedded Linux as the operating system to form the entire system. The system uses Ethernet power supply to realize the function of network broadcasting without the need for a dedicated power supply line.

1 System Structure

The system consists of an audio amplifier LM48510, an audio processor, Ethernet power supply, and Ethernet data communication. From the front end to the back end, it goes through several processing processes such as audio amplifier M48510 → ARM926EJ-S → PoE/Network to realize Ethernet power supply network broadcasting. The hardware structure of the system is shown in Figure 1.

2 System Hardware Design

2.1 ARM926EJ-S related design

The ARM926EJ-S processor is a member of the ARM9 family of general-purpose microprocessors and belongs to the 5TEJ version of the ARM architecture. It is targeted at multi-tasking applications, and full memory management, high performance, small core size and low power consumption are its important features. The ARM926EJ-S processor supports the 32-bit ARM 16-bit Thumb instruction set, allowing users to strike a balance between high performance and high code density. Using the ARM-926EJ-S soft-core processor solution, a comprehensive and configurable buffer storage system is created to enhance the core's needs for consumer electronics such as audio/video, voice and multimedia.

ARM926EJ-S, as the CPU of the system, captures the audio signal from the microphone, realizes the digital audio signal through the audio signal processor, and after the encoding process, transmits it to the external SDRAM through the AHB bus DMA. After the relevant processing by the audio amplifier LM48510, it is sent to the Ethernet MAC and output from the network port to the speaker. In addition, ARM926EJ-S has a wealth of peripherals and I/O, which also provides great convenience for future system upgrades.

2.2 PoE Power Design

2.2.1 Working process of PoE power supply

First, the PSE device outputs a very small voltage at the port until it detects that the connection at the end of the cable is a powered device that supports the IEEE 802.3af standard. After detecting the powered device PD, the PSE device may classify the PD device and evaluate the power consumption required by the PD device. During a configurable startup period (generally less than 15μs), the PSE device starts to power the PD device from a low voltage until a 48 V DC power supply is provided. Provide a stable and reliable 48 V DC power to the PD device to meet the power consumption of the PD device not exceeding 15.4 W. If the PD device is disconnected from the network, the PSE will quickly (generally within 300 to 400 ms) stop powering the PD device and repeat the detection process to detect whether the PD device is connected to the end of the cable. The POE power supply principle diagram is shown in Figure 2.

2.2.2 Ethernet Power Controller LTC4267

Linear Technology introduces the LTC4267, an IEEE 802.3af Ethernet Power (PoE) controller with an integrated switching regulator that greatly simplifies the design of powered devices (PDs). The LTC4267 includes an on-chip DC/DC controller with a constant frequency current mode that is easily customized to meet the requirements of a variety of supply voltages and load currents. Constant frequency operation can be maintained at very light loads, minimizing the low frequency noise generated.

3 System software design

The software system includes the system bootloader, embedded operating system and upper-level applications. The bootloader is the bootloader that runs before the operating system, and its main task is to complete the necessary hardware initialization and operating system loading before the system starts; the operating system is the core program of the entire embedded platform, and its main function is to efficiently manage and allocate the underlying hardware resources and provide upper-level applications with a system call interface that is independent of hardware details.

The system initialization program also completes the system's network allocation, audio-related parameter configuration, and shuts down unused peripherals to minimize power consumption.

The software system also includes TCP/IP and UDP protocol libraries, which are key to network broadcasting. Application software includes file system management, network services, email sending, file transfer, detection and alarm, etc. The network service program sends the voice to a certain port on the network for access by other network devices.

Conclusion

This article introduces the design and implementation of network broadcasting based on the ARM926EJ-S microcontroller. The network power supply module LTCA267 is an on-chip DC/DC controller in constant frequency current mode. The audio amplifier LM48510 does not require an external boost converter to ensure that the output power of the new product remains stable. At present, ARM926EJ-S has a wide range of applications in consumer electronics such as audio/video, voice and multimedia. Therefore, this system has broad application prospects.