Comtrol eCos - Manual (Page 365)

Chapter 14. Introduction
The I/O package is designed as a general purpose framework for supporting device drivers. This includes all classes
of drivers from simple serial to networking stacks and beyond.
Components of the I/O package, such as device drivers, are configured into the system just like all other compo-
nents. Additionally, end users may add their own drivers to this set.
While the set of drivers (and the devices they represent) may be considered static, they must be accessed via an
opaque “handle”. Each device in the system has a unique name and the
cyg_io_lookup() function is used to
map that name onto the handle for the device. This “hiding” of the device implementation allows for generic,
named devices, as well as more flexibility. Also, the
cyg_io_lookup() function provides drivers the opportunity
to initialize the device when usage actually starts.
All devices have a name. The standard provided devices use names such as “/dev/console” and
“/dev/serial0” , where the “/dev/” prefix indicates that this is the name of a device.
The entire I/O package API, as well as the standard set of provided drivers, is written in C.
Basic functions are provided to send data to and receive data from a device. The details of how this is done is left to
the device [class] itself. For example, writing data to a block device like a disk drive may have different semantics
than writing to a serial port.
Additional functions are provided to manipulate the state of the driver and/or the actual device. These functions
are, by design, quite specific to the actual driver.
This driver model supports layering; in other words, a device may actually be created “on top of” another device.
For example, the “tty” (terminal-like) devices are built on top of simple serial devices. The upper layer then has the
flexibility to add features and functions not found at the lower layers. In this case the “tty” device provides for line
buffering and editing not available from the simple serial drivers.
Some drivers will support visibility of the layers they depend upon. The “tty” driver allows information about the
actual serial device to be manipulated by passing get/set config calls that use a serial driver “key” down to the serial
driver itself.
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