設計多線程和多核系統

　　如果您的微控制器應用程序需要處理數字音頻，請考慮采用多線程方法。使用多線程設計方法可以使設計者以簡單的方式重用其部分設計。

　　多核和多線程是設計實時系統的有效方法。使用這些技術，系統被設計成一個多任務的集合，這些任務在需要時獨立運行并相互通信。將系統設計從大型塊代碼分解為更易于管理的任務，大大簡化了系統設計并加快了產品開發速度。因此，整個系統的實時性更容易理解。設計者只需擔心執行每個任務的保真度，并詢問諸如“網絡協議是否正確實現”之類的問題？

　　在本文中，我們將討論如何使用多線程或多核設計方法來設計實時操作數據流的系統，如數字音頻系統。我們用幾個數字音頻系統來說明設計方法，包括異步USB音頻2，AVB以太網和MP3播放器數字碼頭。在討論如何有效地使用多核和多線程來設計緩沖和時鐘方案之前，我們簡要地討論了數字音頻、多核和多線程的概念。

　　Digital audio

　　Digital audio has taken over from analog audio in many consumer markets for two reasons. First， most audio sources are digital. Whether delivered in lossy compressed form （MP3） or in uncompressed formats （CD）， digital standards have taken over from the traditional analog standards such as cassettes and tapes. Second， digital audio is easier to deal with than analog audio. Data can be transferred without loss over existing standards， such as IP or USB， and the hardware design does not need any “magic” to keep the noise floor down. As far as the digital path is concerned， the noise floor is constant and immune from TDMA noise which mobile phones may cause.

　　A digital audio system operates on streams of samples. Each sample represents the amplitude of one or more audio channels at a point in time， with the time between samples being governed by the sample rate. CD standards have two channels （left and right） and use a sample rate of 44.1 kHz. Common audio standards use 2， 6 （5.1）， and 8 （7.1） channels， and sample rates of 44.1 kHz， 48 kHz， or a multiple. We use 48 kHz as a running example， but this is by no means the only standard.