Line Disciplines--Essential Linux Device Drivers--嵌入式linux中文站1

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Line Disciplines

Line disciplines provide an elegant mechanism that lets you use the same serial driver to run different

technologies. The low-level physical driver and the tty driver handle the transfer of data to and from the

supports a raw mode used by editors, which leaves all the preceding processing to user applications. See Figure

7.3 in the next chapter, "Input Drivers," to learn how the keyboard subsystem is connected to N_TTY. The

example tty drivers listed at the end of the previous section, "TTY Drivers," use N_TTY by default.

Line disciplines also implement network interfaces over serial transport protocols. For example, line disciplines

that are part of the Point-to-Point Protocol (N_PPP) and the Serial Line Internet Protocol (N_SLIP) subsystems,

frame packets, allocate and populate associated networking data structures, and pass the data on to the

corresponding network protocol stack. Other line disciplines handle Infrared Data (N_IRDA) and the Bluetooth

Host Control Interface (N_HCI).

Device Example: Touch Controller

Let's take a look at the internals of a line discipline by implementing a simple line discipline for a serial touch-

kernel. Listing 6.2 contains a code snippet that performs both these operations for the example touch

controller.

Code View: