Implementation of digital multi-function board based on DSP

　　1 Introduction

　　Tone board , caller ID display board, multi-frequency inter-control transceiver board, dual audio receiver board, etc. are important common equipment of program-controlled switches. These devices are different hardware boards in program-controlled switches, and these boards all use dedicated integrated circuits (ICs) to realize their functions. However, when adding business functions to a board or the IC used in a board is discontinued, the board manufacturer needs to redesign the hardware circuit. This will increase R&D costs and risks.

Based on this, a digital multifunctional board based on DSP　　is developed with digital signal processing technology as the core, targeting the characteristics of the switch . This board is a DSP hardware single-board platform that can provide a variety of external interfaces. By using different DSP algorithms and microcontroller programs, it processes various signals required by the switch and completes the functions of each single board, which is convenient for maintenance and upgrading, saving development costs and shortening the development cycle. Here, the specific process of realizing the sound board is used as an example to explain in detail.

　　2 Digital Multi-Function Board Architecture and Working Principle

　　2.1 Overall architecture of digital multi-function board

　　The architecture of the digital multifunctional board is divided into two parts: a control unit and a functional unit, as shown in FIG1 .

　　In addition to controlling the DSP of the module, the microcontroller MCU can provide a driven CPU bus to the outside world. The DSP provides a multi-channel buffered serial port MCBSP (Muhi Channel Buffer Serial) and a host parallel interface HPI (Host Parallel Inter-terface). In addition, 3.5 V and 3.3 V power input interfaces are required.

　　MCU is the core control unit, responsible for communicating with the processor and console PC, downloading DSP code to DSP through HPI, and monitoring DSP operation; controlling the switching network MCV device, completing dynamic time slot allocation and conversion between 2 Mbit/s and 8 Mbit/s; and controlling the work of other devices on the MCU expansion bus. DSP is the core functional unit, processing the 8 M-bit TDM audio code stream to achieve specific functions. If the soundboard function is to be realized, the DSP reads and sends the audio signal encoding data, controls the intermittent ratio, and sends the corresponding audio signal in each time slot cycle; receives user-defined audio data, writes it into Flash, replaces the preset voice, and controls the deletion of the white-defined audio and the complete erasure of Flash to achieve flexible modification.

　　2.2 Digital Multi-Function Board Software and Hardware Interface

　　The digital multifunction board provides externally driven MCU standard bus, serial communication interface, multi-channel buffered serial port, etc. Among them, the serial communication interface is used as the download serial port for MCU and DSP programs; McBSP is 2 channels of 8 M-bit TDM code stream input and output of the digital multifunction board. Users can define the serial communication protocol between the digital multifunction board MCU software and the PC download software. The circuit board is designed as a 4-layer wiring in a modular form. The external connection of each interface adopts a standard connector with a pitch of 2.54 mm to improve its interconnectivity. The serial port connection with the PC uses an ordinary serial port line, connecting from the 9-pin socket of the digital multifunction board to the 9-pin socket of the COM port of the PC.

　　2.3 Working principle of digital multi-function board

　　The working principle of the digital multi-function board is analyzed in detail as follows:

　　(1) Code download and online modification The MCU communicates with the DSP (TMS320VC5402) through its HPI interface. The DSP program code is stored as a constant segment in the microcontroller 's on-chip program memory or off-chip data memory, and is downloaded by the microcontroller to the DSP's on-chip RAM via HPI for execution. By executing the code, the DSP completes the function of sending audio signals (including live voice updates). The MCU device characteristics and circuit design enable the contents of the microcontroller's on-chip program memory or off-chip data memory to be modified online, and the new code can be downloaded to the board from the PC via the COM port.

　　(2) Audio Signal Transmission The original audio signal data is pre-stored in the Flash of the DSP plug-in. The DSP reads it out according to certain rules and outputs it in the form of 8M bit rate TDM code stream through the multi-channel buffer serial port McBSP.

　　(3) Live Voice Update The user inputs the recorded voice into the PC program in the form of a WAV file, which is then converted into the required format and transmitted to the MCU via the PC COM port, which is then transferred to the DSP, which finally writes it into the Flash. The board to be updated is required to be in standby mode.

　　2.4 Component Selection

　　To realize the digital multi-function board, it is necessary to select appropriate components, such as microcontroller, DSP , Flash, serial interface, etc. The DSP uses TMS320VC5402, which is a relatively common and cost-effective 16-bit fixed-point DSP with a processing capacity of 100 MI/s; the MCU uses SST89C58, which has 2 Flash blocks inside to realize online modification of the microcontroller and DSP program firmware, and its instructions are compatible with the MCS51 series microcontrollers. It is convenient for development and application; Flash uses TE28F160C3, a 3.3 V memory with basically compatible 16 M-bit, 32 M-bit, and 64 M-bit packages. The RS-232 interface uses a single-channel device MAX3221E. This device can withstand 15 kV electrostatic shock and is not easily damaged in actual use.

　　3 Specific implementation and analysis

　　The sound board program of the digital multi-function board is written in C language, mainly including: communicating with the processor, controlling the switching network, downloading the DSP program code through the HPI interface, and receiving the number detected by the DSP, that is, the program of the MCU MCS51 and the program of the DSP TMS320VC5402. When programming the DSP, the digital signal processing function library DSPLIB of TMS3-20VC5509 is used. DSPLIB includes commonly used digital signal processing functions. All functions are written in assembly language, with a high degree of optimization, and can be called by C programs, which greatly facilitates program programming. Figure 2 is the audio information processing flow. Command "1" means connecting the time slot. According to the tone number in the command (if used for SP30, conversion is performed first), the switching network device is controlled to complete the exchange of the 8M HW time slot in and out; command "4" means disconnecting the time slot channel; command "8" means resetting, and reporting command 8 as a response. The test is mainly to test the interface signal. That is, the sound of each time slot is played out through an oscilloscope or PCM tester. Through testing, it is found that the multi-function board can provide 4 or 8-channel analog carrier relay, and various signal tones and test tones meet the requirements of the "General Technical Specifications for Telephone Exchange Equipment of the Ministry of Posts and Telecommunications".

　　2.3 Working principle of digital multi-function board

　　The working principle of the digital multi-function board is analyzed in detail as follows:

　　(1) Code download and online modification The MCU communicates with the DSP (TMS320VC5402) through its HPI interface. The DSP program code is stored as a constant segment in the microcontroller 's on-chip program memory or off-chip data memory, and is downloaded by the microcontroller to the DSP's on-chip RAM via HPI for execution. By executing the code, the DSP completes the function of sending audio signals (including live voice updates). The MCU device characteristics and circuit design enable the contents of the microcontroller's on-chip program memory or off-chip data memory to be modified online, and the new code can be downloaded to the board from the PC via the COM port.

　　(2) Audio Signal Transmission The original audio signal data is pre-stored in the Flash of the DSP plug-in. The DSP reads it out according to certain rules and outputs it in the form of 8M bit rate TDM code stream through the multi-channel buffer serial port McBSP.

　　(3) Live Voice Update The user inputs the recorded voice into the PC program in the form of a WAV file, which is then converted into the required format and transmitted to the MCU via the PC COM port, which is then transferred to the DSP, which finally writes it into the Flash. The board to be updated is required to be in standby mode.

　　2.4 Component Selection

　　To realize the digital multi-function board, it is necessary to select appropriate components, such as microcontroller , DSP, Flash, serial interface, etc. The DSP uses TMS320VC5402, which is a relatively common and cost-effective 16-bit fixed-point DSP with a processing capacity of 100 MI/s; the MCU uses SST89C58, which has 2 Flash blocks inside to realize the online modification of the microcontroller and DSP program firmware, and its instructions are compatible with the MCS51 series microcontroller. It is convenient for development and application; Flash uses TE28F160C3, a 3.3 V memory with basically compatible 16 M-bit, 32 M-bit, and 64 M-bit packages. The RS-232 interface uses a single-channel device MAX3221E. This device can withstand 15 kV electrostatic shock and is not easily damaged in actual use.

　　3 Specific implementation and analysis

　　The sound board program of the digital multi-function board is written in C language, mainly including: communicating with the processor, controlling the switching network, downloading the DSP program code through the HPI interface, and receiving the number detected by the DSP, that is, the program of the MCU MCS51 and the program of the DSP TMS320VC5402. When programming the DSP, the digital signal processing function library DSPLIB of TMS3-20VC5509 is used. DSPLIB includes commonly used digital signal processing functions. All functions are written in assembly language, with a high degree of optimization, and can be called by C programs, which greatly facilitates program programming. Figure 2 is the audio information processing flow. Command "1" means connecting the time slot. According to the tone number in the command (if used for SP30, conversion is performed first), the switching network device is controlled to complete the exchange of the 8M HW time slot in and out; command "4" means disconnecting the time slot channel; command "8" means resetting, and reporting command 8 as a response. The test is mainly to test the interface signal. That is, the sound of each time slot is played out through an oscilloscope or PCM tester. Through testing, it is found that the multi-function board can provide 4 or 8-channel analog carrier relay, and various signal tones and test tones meet the requirements of the "General Technical Specifications for Telephone Exchange Equipment of the Ministry of Posts and Telecommunications".