Kernel Extensions and Device Support Programming Concepts

Components Affected by the Low Function Terminal Interface

The lft interface impacts the following components:

• Configuration User Commands
• Keyboard Device Driver (Information about this is contained in Graphic Input Device Driver Programming Interface.)
• Display Device Driver
• Rendering Context Manager

Configuration User Commands

The lft interface is a pseudo-device driver. Consequently, the system configuration process does not detect the lft interface as it does an adapter. The system provides for pseudo-device drivers to be started through Config_Rules. To start the lft interface, use the startlft program.

Supported commands include:

• lsfont
• mkfont
• chfont
• lskbd
• chkbd
• lsdisp (see note)
• chdisp (see note)
  Note
  1. lsdisp outputs the logical device name instead of the instance number.
  2. chdisp uses the ioctl interface to the lft to set the requested display.

Display Device Driver

Beginning with AIX 4.1, a display device driver is required for each supported display adapter.

The display device drivers provide all the standard interfaces (such as config, initialize, terminate, and so forth) required in any AIX 4.1 (or later) device drivers. The only device switch table entries supported are open, close, config, and ioctl. All other device switch table entries are set to nodev. In addition, the display device drivers provide a set of ioctls for use by AIXwindows and diagnostics to perform device specific functions such as get bus access, bus memory address, DMA operations, and so forth.

Rendering Context Manager

The Rendering Context Manager (RCM) is a loadable module.

To ensure that lft can recover the display in case AIXwindows should terminate abnormally, AIXwindows issues the ioctl to RCM after opening the pseudo-device. RCM passes on the ioctl to the lft. This way, the close function in RCM is invoked (Because AIXwindows is the only application that has opened RCM), and RCM notifies the lft interface to start reusing the display. To support this communication, the RCM provides the required ioctl support.

The RCM to lft Interface Initialization

1. RCM performs the open /dev/lft.
2. Upon receiving a list of displays from X, RCM passes the information to the lft through an ioctl.
3. RCM resets the adapter.

If AIXwindows Terminates Abnormally

1. RCM receives notification from X about the displays it was using.
2. RCM resets the adapter.
3. RCM passes the information to the lft by way of an ioctl.

AIXwindows to lft Initialization

The AIXwindows to lft initialization includes the following:

1. AIXwindows opens /dev/rcm.
2. AIXwindows gets the gsc_handle from RCM via an ioctl.
3. AIXwindows becomes a graphics process aixgsc (MAKE_GP, ...)
4. AIXwindows, through an ioctl, informs RCM about the displays it wishes to use.
5. AIXwindows opens all of the input devices it needs and passes the same input ring to each of them.

Upon Normal Termination

1. X issues a close to all of the input devices it opened.
2. X informs RCM, through an ioctl, about the displays it was using.

Diagnostics

Diagnostics and other applications that require access to the graphics adapter use the AIXwindows to lft interface.