app609| Application Note
MICROCONTROLLERS TINI - TINY INTERNET INTERFACES
Jan 21, 2003
App Note 609: Internet Speaker with the DS80C400 Silicon Software
The networking capabilities of the DS80C400 microprocessor make it a natural choice for designing a simple Ethernet-enabled speaker. By using the TCP/IP stack built into the processor's ROM, an application written in 8051 assembly can easily read streaming audio data from the network and use that data to drive a digital-to-analog converter (DAC) that provides line-level output for a set of speakers. This application note presents the hardware design and the software necessary to run a simple Ethernet-enabled speaker.
System Overview
Software At the top level, the application consists of a host computer sending uncompressed audio (such as data from a WAV file) over a network connection to a DS80C400, which listens and plays the audio data. Figure 1 shows a block diagram of this system.
Figure 1. System block diagram. There must be two software applications to make this system work. One application must run on the host computer and send audio data to the DS80C400. The other application must run on the DS80C400 and play audio data. The host application has an easy job in this system. It must read raw audio data from a WAV file and send it over the network. Since there is a lot of processing power not being used on the host, it does some other jobs too, like flow control and simple data formatting. The application on the DS80C400 is a little more complicated. It needs to receive audio data over the network, and push that data to an audio circuit at the specified sample rate. Receiving the audio data is implemented in a loop that waits for audio data and writes it to a circular buffer when it becomes available. As it receives new data, it must also maintain a pointer to the end of the valid data in the buffer, so the application does not play invalid data.
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