ARM 到底是什么
ARM 即Advanced RISC Machines的缩写，你可以理解这是一个公司的名称，将这认为是对一类微处理器的通称也是正确的，不仅如此，甚至这还代表的是一种技术。
ARM公司是一家既不生产芯片（fabless）也不销售芯片（chipless）的公司，它通过出售芯片技术授权，建立起新型的微处理器设计、生产和销售商业模式。更重要的是，这种商业模式取得极大的成功，采用ARM技术IP核的微处理器遍及各类电子产品：汽车、消费电子、成像、工业控制、海量存储、网络、安保和无线等市场，ARM技术几乎无处不在。
很多以核为基础的系统芯片设计都以ARM核为基础。尽管Intel的微处理器在PC领域处于压倒优势地位，但在嵌入系统领域，Intel利用了ARM核的技术授权，例如，推出基于ARM的MP3播放器，Intel与TI在2001年7月30日同时取得ARM V6结构的授权。
许多半导体公司持有ARM 授权：Atmel、Broadcom、Cirrus Logic、Freescale（于2004从摩托罗拉公司独立出来）、Qualcomm、富士通、英特尔（借由和Digital的控诉调停）、IBM，英飞凌科技，任天堂，恩智浦半导体（于2006年从飞利浦独立出来）、OKI电气工业，三星电子，Sharp，STMicroelectronics，德州仪器和VLSI等许多这些公司均拥有各个不同形式的ARM授权。利用这种合伙关系，ARM很快成为许多全球性RISC标准的缔造者。
虽然ARM的授权项目由保密合约所涵盖，在智慧财产权工业，ARM是广为人知最昂贵的CPU内核之一。单一的客户产品包含一个基本的ARM 内核可能就需索取一次高达美金20万的授权费用。而若是牵涉到大量架构上修改，则费用就可能超过千万美元。每个厂商得到的都是一套独一无二的ARM相关技术及服务。
ARM（Asynchronous
Resbonse
Mode：异步响应方式）也是一种非平衡数据链路操作方式，与NRM不同的是，ARM下的传输过程由从站启动。从站主动发送给主站的一个或一组帧中可包含有信息，也可以是仅以控制为目的而发的帧。在这种操作方式下，由从站来控制超时和重发。该方式对采用轮询方式的多站链路来说是必不可少的。
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