IBM6153(4)

NAME
ibm6153, apa8 - IBM 6153 Advanced Monochrome Graphics Display interface

SYNOPSIS
pseudo-device apa8

DESCRIPTION
The IBM 6153 Advanced Monochrome Graphics Display is a 12-inch CRT with gray-white phosphor, driven at 92 Hz interlaced. It provides a monochrome, all-points-addressable, bit-mapped display with 393,216 points on the screen (768 displayable pixels on each of 512 displayable lines). All pixels are directly accessible by the CPU. The display adapter provides hardware assist features including a write mask to protect bit fields within a byte, a barrel shifter to rotate bits within a byte, and a logic unit to combine source bytes before they are written into the bit map.

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 (beginning at 0xf4d00000), and 16 bytes of I/O space (addressed from 0x160 through 0x16f). The 128KB block defines both the visible frame buffer and the hidden, off-screen memory area. For each of the 512 scan lines, the first 90 bytes (720 pixels) are visible; the last 38 bytes (304 pixels) are hidden. The 16 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 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 picture data, accessing display buffers, etc. When a process opens /dev/apa8, 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/apa8 is closed.

FILES
/dev/apa8
/dev/console

SEE ALSO
cons(4), ibm5151(4), ibm6155(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/apa8 is not limited to the apa-8 addresses.