設(shè)計(jì)多線程和多核系統(tǒng)

　　如果您的微控制器應(yīng)用程序需要處理數(shù)字音頻，請(qǐng)考慮采用多線程方法。使用多線程設(shè)計(jì)方法可以使設(shè)計(jì)者以簡(jiǎn)單的方式重用其部分設(shè)計(jì)。

　　多核和多線程是設(shè)計(jì)實(shí)時(shí)系統(tǒng)的有效方法。使用這些技術(shù)，系統(tǒng)被設(shè)計(jì)成一個(gè)多任務(wù)的集合，這些任務(wù)在需要時(shí)獨(dú)立運(yùn)行并相互通信。將系統(tǒng)設(shè)計(jì)從大型塊代碼分解為更易于管理的任務(wù)，大大簡(jiǎn)化了系統(tǒng)設(shè)計(jì)并加快了產(chǎn)品開(kāi)發(fā)速度。因此，整個(gè)系統(tǒng)的實(shí)時(shí)性更容易理解。設(shè)計(jì)者只需擔(dān)心執(zhí)行每個(gè)任務(wù)的保真度，并詢問(wèn)諸如“網(wǎng)絡(luò)協(xié)議是否正確實(shí)現(xiàn)”之類的問(wèn)題？

　　在本文中，我們將討論如何使用多線程或多核設(shè)計(jì)方法來(lái)設(shè)計(jì)實(shí)時(shí)操作數(shù)據(jù)流的系統(tǒng)，如數(shù)字音頻系統(tǒng)。我們用幾個(gè)數(shù)字音頻系統(tǒng)來(lái)說(shuō)明設(shè)計(jì)方法，包括異步USB音頻2，AVB以太網(wǎng)和MP3播放器數(shù)字碼頭。在討論如何有效地使用多核和多線程來(lái)設(shè)計(jì)緩沖和時(shí)鐘方案之前，我們簡(jiǎn)要地討論了數(shù)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.