IBM6155(4)

NAME
ibm6155, apa16 - IBM 6155 Extended Monochrome Graphics Display interface

SYNOPSIS
pseudo-device apa16

DESCRIPTION
The IBM 6155 Extended Monochrome Graphics Display is a 15-inch CRT with gray-white phosphor, driven at 60 Hz non-interlaced. It provides a monochrome, all-points-addressable, bit-mapped display with 786,432 points on the screen (1024 pixels on each of 768 displayable lines). All pixels are directly accessible by the workstation's CPU. A fast raster-operation processor is provided with built-in capability for bit-block transfer, line draw, image copy/merge and image rotate. A graphics queue mechanism with synchronization and controlled branching allows pre-programmed graphics subroutines. A 48x64-bit hardware cursor provides instant cursor operations without disruption of display data.

The display adapter is a single PC/AT card installed in the I/O bus as a sixteen-bit device. The display appears to the system as two separate memory areas: a 128-kilobyte block of system memory, and 20 bytes of I/O space (addressed from 0xd10 through 0xd2f, and 0x6f3). The 128KB block defines both the visible frame buffer (addressed from 0xf4d80000 through 0xf4d97ffe) and the hidden, off-screen memory area (addressed from 0xf4d98000 through 0xf4d9fffe). The 20 bytes of I/O space access the display adapter's control registers.

The display operates in glass tty (the default) mode and window-manager mode:

-   Glass tty mode initialization consists of the downloading of a character font and certain graphics subroutines into the adapter card, followed by a cursor home and screen clear. In this mode, the display driver emulates a smart terminal, similar to an IBM 3101, and can be /dev/console.

-   In window-manager mode, a user-level process, such as a window manager, can directly control the display device hardware, loading control programs, accessing display buffers, etc. When a process opens /dev/apa16, the kernel switches console output to another display device, if available, or buffers the output until later (see cons(4)). At this point, the display and control memory areas are accessible for manipulation by the user program. Glass tty mode is reentered when /dev/apa16 is closed.

FILES
/dev/apa16
/dev/console

SEE ALSO
cons(4), ibm5151(4), ibm6153(4), ibmaed(4), keyboard(4), tty(4)

DIAGNOSTICS
None.

ERRORS
The following errors can be returned by the interface:

[ENODEV]
    Nonexistent display (on open, close, read, write, or ioctl);
    Unavailable display (on open): user processes are denied access to this display (see consoles(5), setscreen(8)).

[EIO]
    Made an attempt to close a display device that was not open.

[EBUSY]
    The display has already been opened by a user process.

BUGS
Access to the PC/AT I/O and memory busses through /dev/apa16 is not limited to the apa-16 addresses.