> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/4.3-bsd-unix-cao-zuo-xi-tong-she-ji-yu-shi-xian/di-san-bu-fen-io-xi-tong/9.9.-qi-ta-hang-gui-cheng.md).

# 9.9 其他行规程

我们用标准面向终端的行规程例程考察了终端 I/O 系统的运作——这些例程既实现伯克利的新行规程，也实现第七版 UNIX 的旧行规程。为求完整，现在描述系统中的其他几种行规程。注意，前文对终端多路复用驱动运作的讨论，对这些规程与对面向终端的规程同样适用。

**Berknet**

串行线替代用途的第一个替代行规程例子是 Berknet 行规程。*Berknet* 是一个已废弃的面向批处理的网络，曾用 9600 波特串行线连接 PDP-11 与 VAX 的 UNIX 系统。由于标准行规程输入处理的开销，人们设计了一种功能精简的专用网络规程：提供七位数据通路传输以换行结尾的数据块；确认与校验和在系统之外完成。Berknet 规程为每条线路分配单个缓冲，一次缓冲一行输入（网络软件每确认一行才允许发下一行）。`l_rint` 收字符例程在多数多路复用驱动中展开内联，以尽量压缩开销。

**串行线路 IP 规程**

另一种行规程——串行线路 IP（Serial Line IP，SLIP）——供更现代的网络软件在异步串行线上封装和传输网际协议（IP）数据报 \[Romkey, 1988]。（IP 的资料见第 11、12 章。）**slattach** 程序打开一条串行线路，设置线路速度，进入 SLIP 行规程。SLIP 行规程的 open 例程把终端线路与一个预配置的网络接口关联，准备收发网络分组。用 **ifconfig** 程序设置接口的网络地址后，网络就会经 SLIP 线路路由分组，到达线路所连的系统。分组用简单的方案成帧：一个成帧字符（八进制 0300）分隔分组。分组内部出现的成帧字符用转义字符（八进制 0333）引用并换位（为八进制 0334）；分组内的转义字符同样转义并换位（为八进制 0335）。

每次向 SLIP 接口输出分组时启动输出通路。SLIP 规程把成帧字符和分组数据放上 `tty` 的输出队列，按需转义成帧和转义字符，然后调用 `ttstart()` 启动传输——后者转而调用 `tty_t_oproc` 字段引用的设备启动例程。只要队列空间够、系统不缺 C-list 块，它可以在返回前放上多个分组。传输完成时，设备驱动调用 SLIP 的 start 例程，继续往输出队列放数据，直到全部分组发出或队列再次填满。

使用 SLIP 规程的线路上收到字符时，被转义的字符翻译回来，数据字符放进网络缓冲。成帧字符结束分组时，分组交给网络，缓冲重新初始化。

SLIP 规程让没有专门高速网络硬件的机器也能获得中等速度的网络连接。

**图形输入板规程**

tablet 行规程用来经串行线把数字化仪等图形设备接入系统。进入规程后，它持续从设备接收图形数据，允许应用程序从线路读取来轮询最新信息。返回信息的格式取决于设备提供的形式；支持多种格式。


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