Audio system based on PXA272 and TSC2101 under Windows CE system

Windows CE is an open, customizable, 32-bit real-time embedded operating system. It has the characteristics of good reliability, high real-time performance and small kernel size, so it is widely used in the development of various embedded intelligent devices. Its applications involve various fields such as industrial control, information appliances, mobile communications, automotive electronics, personal electronic consumer products, etc. It is the most widely used and fastest growing embedded operating system today. In these embedded applications, audio modules have become an indispensable part of most products. This article constructs an audio system based on Intel Xscale PXA272 and TSC2101 audio chips for the Windows CE operating system, and briefly introduces its implementation method.

Hardware implementation of audio system

The audio driver in this design is implemented using the Unified Audio model, based on the Intel Xscale PXA272 processor and TI's TSC2101 audio chip, and uses an audio system architecture based on the I2S (Inter-IC Sound) bus. The system schematic is shown in Figure 1. The Intel Xscale PXA272 chip integrates an I2S controller and processes audio data through the I2S bus. Other signals (such as control signals) need to be transmitted separately. In this design, the SSP serial port of the Xscale PXA272 chip is configured as an SPI serial port to achieve the transmission of control signals.

Figure 1 System Schematic Diagram

I2S is a serial digital audio bus protocol proposed by Philips. The I2S controller of PXA272 controls the I2S link. The I2S controller consists of data buffer, status and control registers, and counters. They connect the system memory and the peripheral audio decoder chip (TSC2101) to generate synchronous audio. When playing audio files, the I2S controller sends the digitized sound samples in the system memory to the peripheral TSC2101 audio decoder chip through the I2SLINK connection, and then the digital-to-analog converter of the TSC2101 chip converts the digital audio signal into an analog signal.

For recording, the I2S controller receives digital signals from the external TSC2101 audio chip and stores them in the system memory. I2S provides both normal I2S and MSB-justified-I2S formats. The I2S controller of the TSC2101 chip and the PXA272 is connected via 5 pins to form a channel for audio data transmission. The necessary signals of the I2S controller are: a bit rate clock, which can reference an external or internal clock source; a control signal that provides "left/right" channel control information; two serial audio pins, one output and one input; bit rate clock, the I2S controller will also send the optional system clock signal to the external decoder.

The I2S controller is accessed through DMA mode. In DMA mode, the DMA controller can only access the FIFO through the serial audio data register (SADR). The DMA controller usually accesses the FIFO queue data in blocks of 8, 16 or 32 bytes.

The audio chip TSC2101 used in this design integrates stereo audio decoding and touch screen control chips. The stereo DAC can play audio files at a sampling rate of up to 48Kb/s, and is specially designed for PDAs, PMPs, smart phones and MP3 players. TSC2101 integrates speaker amplifiers, headphone amplifiers and four-wire touch screen controllers with audio codecs, and has a stereo headset transceiver interface, a mobile phone transceiver interface, a mono 8Ω speaker amplifier and a 32Ω receiver driver, and integrates a battery monitor and an on-chip temperature sensor.

The circuit design of the TSC2101 chip is shown in Figure 2.

Figure 2 TSC2101 chip circuit design

This design is the application of TSC2101 in smart phones. CP-IN is the voice input of the communication module, and CP-OUT is the output of the audio system to the communication module. In actual applications, MIC1 can be connected to CP-OUT through the internal PGA (programmable gain amplifier) ​​and AGC (automatic gain control) circuits of TSC2101 to realize the microphone function of smart phones; at the same time, MIC1 input can also sample the voice data through the internal ADC and transmit it to the processor storage space via the I2S bus to realize the recording function. Of course, while the smart phone is talking, the call recording function can also be realized. Pins 38 to 41 in the circuit diagram are SPI interfaces, pins 42 to 46 are I2S control pins, pins 9 to 12 are touch screen inputs, pins 27 and 28 are audio outputs that can be connected to headphones, pin 26 is connected to the mobile phone receiver, and pins 33 and 35 are connected to external speakers.

Using the Unified Audio model to implement audio driver

The implementation methods of audio drivers include MDD-PDD layered mode and non-layered Unified Audio model. MDD-PDD is a method to directly implement the stream interface, using the model device driver provided by Microsoft