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Explain why you'd use these functions. Some formatting cleanup.

This commit is contained in:
gmcgarry 2002-02-20 20:40:48 +00:00
parent 6728d906e9
commit f82c84c49c
1 changed files with 25 additions and 10 deletions
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35
lib/libarch/i386/i386_get_mtrr.2
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@ -1,4 +1,4 @@
.\" $NetBSD: i386_get_mtrr.2,v 1.5 2002/02/08 01:28:13 ross Exp $ .\" $NetBSD: i386_get_mtrr.2,v 1.6 2002/02/20 20:40:48 gmcgarry Exp $
.\" .\"
.\" Copyright (c) 2001 The NetBSD Foundation, Inc. .\" Copyright (c) 2001 The NetBSD Foundation, Inc.
.\" All rights reserved. .\" All rights reserved.
@ -53,7 +53,15 @@
.Fn i386_set_mtrr "struct mtrr *mtrrp" "int *n" .Fn i386_set_mtrr "struct mtrr *mtrrp" "int *n"
.Sh DESCRIPTION .Sh DESCRIPTION
These functions provide an interface to the MTRR registers found on These functions provide an interface to the MTRR registers found on
686-class processors. 686-class processors for controlling processor access to memory ranges.
This is most useful for accessing devices such as video accelerators
on
.Xr pci 4
and
.Xr agp 4
busses. For example, enabling write-combining allows bus-write transfers
to be combined into a larger transfer before bursting over the bus. This
can increase performance of write operations 2.5 times or more.
.Pp .Pp
.Fa mtrrp .Fa mtrrp
is a pointer to one or more mtrr structures, as described below. The is a pointer to one or more mtrr structures, as described below. The
@ -103,15 +111,15 @@ are:
.Pp .Pp
.Bl -tag -offset indent -width MTRR_TYPE_UNDEF1 -compact .Bl -tag -offset indent -width MTRR_TYPE_UNDEF1 -compact
.It MTRR_TYPE_UC .It MTRR_TYPE_UC
uncached memory. uncached memory
.It MTRR_TYPE_WC .It MTRR_TYPE_WC
use write-combining. use write-combining
.It MTRR_TYPE_WT .It MTRR_TYPE_WT
use write-through caching. use write-through caching
.It MTRR_TYPE_WP .It MTRR_TYPE_WP
write-protected memory. write-protected memory
.It MTRR_TYPE_WB .It MTRR_TYPE_WB
use write-back caching. use write-back caching
.El .El
.Pp .Pp
Valid values for Valid values for
@ -120,11 +128,11 @@ are:
.Pp .Pp
.Bl -tag -offset indent -width MTRR_PRIVATE -compact .Bl -tag -offset indent -width MTRR_PRIVATE -compact
.It MTRR_PRIVATE .It MTRR_PRIVATE
own range, reset the MTRR when the current process exits. own range, reset the MTRR when the current process exits
.It MTRR_FIXED .It MTRR_FIXED
use fixed range MTRR. use fixed range MTRR
.It MTRR_VALID .It MTRR_VALID
entry is valid. entry is valid
.El .El
.Pp .Pp
The The
@ -155,3 +163,10 @@ is invalid.
.It Bq Er EBUSY .It Bq Er EBUSY
No unused MTRRs are available. No unused MTRRs are available.
.El .El
.Sh HISTORY
The
.Fn i386_get_mtrr
and
.Fn i386_set_mtrr
functions appeared in
.Nx 1.6 .