Php Serial Port Communication Linux Operating
Serial Port Programming on Linux. In this tutorial we are going to use the C language to program the serial port on a Linux Operating system. If you are not comfortable with C,you can check our tutorial on Serial Communication using Python.
Contents • • • • • • • • • • • • • • • • • • • • • • • • • • • • The Classic Unix C APIs for Serial Communication [ ] Introduction [ ] Scope [ ] This page is about the classic Unix C APIs for controlling serial devices. Languages other than C might provide appropriate wrappers to these APIs which look similar, or come with their own abstraction (e.g. Nevertheless, these APIs are the lowest level of abstraction one can find for serial I/O in Unix. And, in fact they are also the highest abstraction in C on standard Unix. Some Unix versions ship additional vendor-specific proprietary high-level APIs.
These APIs are not discussed here. Actual implementations of classic Unix serial APIs do vary in practice, due to the different versions of Unix and its clones, like Linux.
Therefore, this module just provides a general outline. It is highly recommended that you study a particular Unix version's manual (man pages) when programming for a serial device in Unix. The relevant man pages are not too great a read, but they are usually complete in their listing of options and parameters. Together with this overview it should be possible to implement programs doing serial I/O under Unix. Basics [ ] Linux, or any Unix, is a multi-user, multi-tasking operating system. As such, programs usually don't, and are usually not allowed to, access hardware resources like serial UARTs directly.
Instead, the operating system provides • low-level drivers for mapping the device into the file system ( /dev and/or /device/ file system entries), • the standard system calls for opening, reading, writing, and closing the device, and • the standard system call for controlling a device, and/or • high-level C libraries for controlling the device. The low-level driver not only maps the device into the file system with the help of the kernel, it also encapsulates the particular hardware. The user often does not even know or care what type of UART is in use. Classic Unix systems often provide two different device nodes (or minor numbers) for serial I/O hardware. These provide access to the same physical device via two different names in the /dev hierarchy. Which node is used affects how certain serial control signals, such as DCD (data carrier detect), are handled when the device is opened. In some cases this can be changed programmatically, making the difference largely irrelevant. Touchpad driver for acer aspire e 15 touch.
As a consequence, Linux only provides the different devices for legacy programs. Device names in the file system can vary, even on the same Unix system, as they are simply aliases. The important parts of a device name (such as in /dev) are the major and minor numbers.
The major number distinguishes a serial port, for example, from a keyboard driver, and is used to select the correct driver in the kernel. Note that the major number differs between different Unix systems.
Php Serial Port Communication Linux Operating System
The minor number is interpreted by the device driver itself. For serial device drivers, it is typically used to detect which physical interface to use. Sometimes, the minor number will also be used by the device driver to determine the DCD behavior or the hardware flow control signals to be used. The typical (but not standardized, see above) device names under Unix for serial interfaces are: /dev/tty xxx Normal, generic access to the device. Used for terminal and other serial communication (originally for tele types). More recently, they are also used in modem communication, for example, whereas the /dev/cua xxx was used on older systems. See the following module on how terminal I/O and serial I/O relate on Unix.
/dev/cua xxx Legacy device driver with special DCD handling. Typically this was used for accessing a modem on old Unix systems, such as running the communication protocol over the serial line and the modem. The cu in the name stands for the [[# cu]] program. The a for ACU (automatic call unit). The xxx part in the names above is typically a one or two digit number, or a lowercase letter, starting at 'a' for the first interface. PC-based Unix systems often mimic the DOS/Windows naming for the devices and call them /dev/com xxx. Linux system generally call serial ports /dev/ttyS xxx instead.
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