Analysis of CS485xx digital audio DSP processing scheme

Cirrus' CS485xx DSP family offers high performance post processing and digital audio mixing. The dual clock domain provided on the PCM input allows mixing of audio streams of different sampling frequencies. The low-power standby mode extends battery life, making it suitable for applications such as car audio systems that are often turned on but do not require audio processing.

The CS485xx family consists of three devices, CS48520, CS48540, and CS48560, with differences between the available inputs and outputs. All DSPs support dual input clock control and dual audio processing paths and are available in a 48-pin QFP package.

Figure 1 CS48500 system block diagram

Figure 2 Block diagram of the CDB48500-USB evaluation board

Main features of the CS485xx series

Low cost, high performance 32-bit DSP

- 300 000 000 MAC/s (multiply accumulation per second)

- Dual MAC cycles per clock

- 72-bit accelerator is more accurate in industrial applications

- 24k&TImes; 32 SRAM, 2k block development data or program

- Internal ROM includes a variety of configurable sound enhancement instruction sets

- 8-channel internal DMA

- Internal watchdog DSP lock blocking

DSP Toolbox w/Personal Key is used to protect consumer IP

- Configurable serial audio input/output

- Maximum 32 bits @192kHz

- Support for 32-bit audio sampling I/O between DSP chips

- TDM input mode (multiple channels on the same line)

- 192kHz SPDIF transmitter

Multi-channel DSD direct bit stream digital SACD input

Supports two different input Fs sampling rates

- Output can be in master mode or slave mode

- Dual processing path capability

- Input support dual domain slave clock

- Hardware assisted time sampling to accommodate sample rate changes

Integrated Always Manager / PLL

- Can be activated from external quartz, external oscillator

Input Fs audio detection

Host control and booting via serial interface

Configurable Hungry GPIO and External Interrupt Input

1.8V core and 3.3VI/O can receive up to 5V input

Low power mode

- Meets the "Energy Star" requirement in low power mode, standby power consumption is 268μW

Figure 3 CDB48500-USB evaluation board connection diagram

CS485xx series target application

Digital Television

Multimedia peripherals

iPod

Head component

Automotive external amplifier

HD-DVD & Blu-ray Disc DVD Receiver

PC speaker

CDB48500-USB Evaluation Board

Each CDB48500-USB evaluation board includes:

CDB48500 development board

Power supply: +9V, 1.67A, 100V~240V, with AC power cord

CDB USB main digital I/O card

USB cable

Three-plate superposition is used to determine the output of CS48520, CS48540 and CS48560

CDB48500-USB Evaluation Board Features

PC control of CS485XX using DSP Composer graphical user interface

Serial control of audio devices on the CDB48500 via I2C or SPI protocol

Digital audio input to PCM via optical or coaxial S/PDIF (compressed data input not supported)

Up to 12 channels of analog audio input via two CS42448 audio codecs

Up to 12 channels of analog audio output with two CS42448 audio codecs

Digital audio output of PCm via optical S/PDIF

Headphone output jack

Multi-channel digital audio input via CDB USB MASTER card (not yet supported)

Separate input and output clock domains for 1FS to 2FS audio processing on CS485xx

Fast boot from consumer applications for 4Mbits serial SPI flash devices - Host Control Master Boot (HCMB)

Microphone input with integrated amplifier for intelligent room calibration (IRC) evaluation (future)

Supports all CS485xx series products in 48-pin LQFP package

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