August 2017
Intermediate to advanced
272 pages
5h 32m
Chinese
Content preview from Node.js物聯網裝置開發
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低功耗藍牙通訊協定
|
205
從軟體的角度來看，我們感興趣的藍牙協定疊層部分位於上面的應用層級。但底下各個
層級，對於應用程式設計來說也很重要，特別是當你想要為專案產品購置硬體的時候。
依據圖 13-1，我們可把藍牙協定疊層分為三大層：
應用層
應用程式經由藍牙和遠端裝置進行傳輸（例如，詢問或提供資料），若想理解其中的
溝通過程，請把應用程式之間的對話想像為一連串的位元組。這些一連串的位元組
可有兩種模式，其一為廣告屬性供「掃描（scan）」裝置，另一種則是搭建裝置之間
的連線。
主機層
為了識別一連串的位元組有何意義，藍牙規格制定諸多定義，例如「泛用型規範」
與「屬性項」。提供關於廣播裝置的資訊，如它是支手錶還是座檯燈。
控制器層
位於最低的層級（
https://developer.bluetooth.org/TechnologyOverview/Pages/HCI.aspx
），
此處雖傳輸資料、但完全無視資料的內容意義，其中有電子電路，以及負責處理藍
牙電波訊號的 IC 晶片。
主機與控制器有可能分開、也有可能整合在同一塊晶片上。主機與控制器之間的橋接介
面，稱為「主機 - 控制器 - 介面（Host-Controller-Interface, HCI）」，圍繞著這個介面，
有著許多輔助工具供我們利用，例如
hcitool
。
若要了解主機層與應用成各個面向，就必須仔細看看裝置之間的傳輸模式，可幫助讀者
通透明白何謂藍牙裝置的規範與屬性項。
傳輸模式
藍牙裝置進行傳輸時，可扮演
中央
（
central
）或
周邊
（
peripheral ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.