ik.4

早期freebsd实现

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.\"     @(#)ik.4	8.1 (Berkeley) 6/5/93
.\"
.Dd June 5, 1993
.Dt IK 4 vax
.Os BSD 4.2
.Sh NAME
.Nm ik
.Nd "Ikonas frame buffer, graphics device interface"
.Sh SYNOPSIS
.Cd "device ik0 at uba? csr 0172460 vector ikintr"
.Sh DESCRIPTION
The
.Nm ik
driver
provides an interface to an Ikonas frame buffer graphics device.
Each minor device is a different frame buffer interface board.
When the device is opened, its interface registers are mapped,
via virtual memory, into the user processes address space.
This allows the user process very high bandwidth to the frame buffer
with no system call overhead.
.Pp
Bytes written or read from the device are
.Tn DMA Ns 'ed
from or to the interface.
The frame buffer
.Tn XY
address, its addressing mode, etc. must be set up by the
user process before calling write or read.
.Pp
Other communication with the driver is via ioctls.
The
.Dv IK_GETADDR
.Xr ioctl 2
returns the virtual address where the user process can
find the interface registers.
The
.Dv IK_WAITINT
.Xr ioctl
suspends the user process until the ikonas device
has interrupted (for whatever reason \(em the user process has to set
the interrupt enables).
.Sh FILES
.Bl -tag -width /dev/ikxx -compact
.It Pa /dev/ik
.El
.Sh DIAGNOSTICS
None.
.Sh HISTORY
The
.Nm
driver appeared in
.Bx 4.2 .
.Sh BUGS
An invalid access (e.g., longword) to a mapped interface register
can cause the system to crash with a machine check.
A user process could possibly cause infinite interrupts hence
bringing things to a crawl.