React Quickly or Feel the Pain

　　很多工作我們在XMOS是關(guān)于“實時編程”，它是退一步思考，這實際上意味著什么。一般來說，實時編程是一種系統(tǒng)，其中系統(tǒng)的某些操作必須滿足特定的截止日期。這些期限可能是系統(tǒng)內(nèi)部或外部的。通常，這種系統(tǒng)被分成“軟”或“硬”實時。如果截止期錯過，硬實時系統(tǒng)會發(fā)生災(zāi)難性的故障，而如果錯過了截止期，軟實時系統(tǒng)會出現(xiàn)質(zhì)量下降，但系統(tǒng)至少可以繼續(xù)工作。

　　處理實時系統(tǒng)時的關(guān)鍵特性是響應(yīng)時間。一個系統(tǒng)的響應(yīng)時間僅僅是對外部刺激的響應(yīng)需要多長時間。這是我們想在XMOS很多。

　　有一個流行的兒童游戲的典型響應(yīng)時間。它有時被稱為“紅手”或“打”，但都在不同的世界各地的其他名稱。它包括兩個人把手放在他們面前，手掌合十，好像在祈禱。球員們把手向前伸，互相觸摸指尖。

　　The game has a “slapper” and an “avoider”。 The aim for the slapper is to break contact and slap the avoider’s hands as hard as possible. The avoider needs to move their hands out of the way before they are slapped - if they do this successfully then the avoider becomes the slapper and get their chance at revenge.

　　This game is a great example of a real-time system and a need for a good response time. The slapper provides the external stimulus， and the avoider is the real-time system that must respond. Similarly， in electronic hard real-time systems， sometimes you need to be able to respond quickly or really feel that pain.