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AIX Version 4.3 Kernel Extensions and Device Support Programming Concepts

Low Function Terminal Interface Functional Description

This section covers the lft interface functional description:


The lft interface uses the common define, undefine, and unconfig methods standard for most devices.

Note: The lft interface does not support any change method for dynamically changing the lft configuration. Instead, use the -P flag with the chdev command. The changes become effective the next time the lft interface is configured.

The configuration process for the lft opens all display device drivers. To define the default display and console, select the default display and console during the console configuration process. If a graphics display is chosen as the system console, it automatically becomes the default display. The lft interface displays text on the default display.

The configuration process for the lft interface queries the ODM database for the available fonts and software keyboard map for the current session.

Terminal Emulation

The lft interface is a stream-based tty subsystem. The lft interface provides VT100 (or IBM 3151) terminal emulation for the standard part of the ANSI 3.64 data stream. All line discipline handling is performed in the layers above the lft interface. The lft interface does not support virtual terminals.

The lft interface supports multiple fonts to handle the different screen sizes and resolutions necessary in providing a 25x80 character display on various display adapters.

Note: Applications requiring hft extensions need to use aixterm.

IOCTLS Needed for AIXwindow Support

AIXwindows and the lft interface share the system keyboard and display device drivers. To prevent screen and keyboard inconsistencies, a set of ioctls coordinates usage between AIXwindows and the lft interface. On a system with multiple displays, the lft interface can still use the default display as long as AIXwindows is using another display.

Note: The lft interface provides ioctl support to set and change the default display.

Low Function Terminal to System Keyboard Interface

The lft interface with the system keyboard uses an input ring mechanism. The details of the keyboard driver ioctls, as well as the format and description of this input ring, are provided in the "Graphic Input Device Driver Programming Interface". The keyboard device driver passes raw keystrokes to the lft interface. These keystrokes are converted to the appropriate code point using keyboard tables. The use of keyboard-language-dependent keyboard tables ensures that the lft interface provides National Language Support.

Note: The keystroke conversion and the keyboard tables are the same used by the hft interface in AIX Version 3.

Low Function Terminal to Display Device Driver Interface

The lft uses a device independent interface known as the virtual display driver (vdd) interface. Because the lft interface has no virtual terminal or monitor mode support, some of the vdd entry points are not used by the lft.

The display drivers might enqueue font request through the font process started during lft initialization. The font process pins and unpins the requested fonts for DMA to the display adapter.

Low Function Terminal Device Driver Entry Points

The lft interface supports the open, close, read, write, ioctl, and configuration entry points.

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