Hardware/Software Co-Design Of Audio Codec Based On OpenRISC

This thesis is on the researching of design and implementation of a low power dissipation audio codec based on OpenRISC. We adopt several software and hardware co-design approaches to accomplish the DVB-oriented audio codec design, and brings up a more flexible and more efficient one, the extended instruction code design approach, to the multi-standard low power audio codec.In this thesis, the sub-band analysis is taken on the MPEG-1/2 BC key coding process and the MDCT is also analyzed. By optimizing the process of filter algorithm of the standard sub-band, adopting the FFT and rearranging the sequence of the add-window procedure, only half of the filter factors need be calculated, consequently the operand, the temporary data storage and the decodec memory access are reduced. In order to improve the complicated decoding process, this article brings up a new way. According to the feature of the prefix of the Huffman code, the code table is reformed, and the loaded code words are indexed, so that the code value could be figured out in two searches.There are three aspects of optimization of the MPEG-1/2 software decodec: decoding procedure, algorithm, assemble level. By analyzing the dynamic range of the decodec factor, it takes different precise fixed quantification on the factor with a large scale. Consequently the software low power dissipation and high quality audio decodec is implemented.In the DVB-oriented decodec design, the CPU ability is beyond the basic task demands; accordingly the main part of the decodec is assigned to the CPU. Meanwhile, the getbits module (indefinite bit read data) is implemented by the hardware coprocessor. This design not only accomplishes the getbits function, but also brings a DMA channel to the audio decoding software, and the operational bottleneck of the decodec is resolved by the hardware as well. In this thesis, the traditional audio and video synchronization control is assigned to the CPU, which makes the synchronization more flexible and the module design simplified.According to the design target, the multi-standard low power dissipation audio codec, a new approach, the extended instruction code set design approach, which is based on the OpenRISC, is brought up. In this thesis, MPEG-1/2 BC, MPEG-4 AAC and the AC-3 audio standards are taken as samples. By analyzing the decoding complexity, a number of key assemble codes which are frequently loaded in each standard are abstracted, so that they could be extended as the specified codes to implement the high efficient multi-standard audio codec in follow tasks.