NetBSD-5.0.2/share/man/man4/geodeide.4

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.\" Copyright (c) 2004 Manuel Bouyer.
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.Dd July 5, 2005
.Dt GEODEIDE 4
.Os
.Sh NAME
.Nm geodeide
.Nd AMD Geode IDE disk controllers driver
.Sh SYNOPSIS
.Cd "geodeide* at pci? dev ? function ? flags 0x0000"
.Sh DESCRIPTION
The
.Nm
driver supports the
.Tn AMD
Geode CS5530A and SC1100
.Tn IDE
controllers,
and provides the interface with the hardware for the
.Xr ata 4
driver.
.Pp
The 0x0002 flag forces the
.Nm
driver to disable
.Tn DMA
on chipsets for which
.Tn DMA
would normally be enabled.
This can be used as a debugging aid, or to work around
problems where the
.Tn IDE
controller is wired up to the system incorrectly.
.Sh SEE ALSO
.Xr ata 4 ,
.Xr atapi 4 ,
.Xr intro 4 ,
.Xr pci 4 ,
.Xr pciide 4 ,
.Xr wd 4 ,
.Xr wdc 4
.Sh BUGS
The SC1100 controller requires 4-byte aligned data transfers and
cannot handle transfers of exactly 64 kilobytes.
.Pp
The CS5530 multifunction chip/core's
.Tn IDE
section claims to be capable of
.Tn UDMA
mode 2
.Pq 33.3MB/s
but in practice using that mode swamps the controller so badly that
.Nm
limits the
.Tn UDMA
negotiation to mode 1
.Pq 25MB/s
so that the other functions of this chip continue to work.
.Pp
The
.Tn IDE DMA
engine in the CS5530 can only do transfers on cache-line
.Pq 16-byte
boundaries.
Attempts to perform
.Tn DMA
on any other alignment will crash the system.
This problem may also exist in the SC1100 since the CS5530 was its
direct predecessor, and it is not clear that National Semiconductor
fixed any bugs in it.
.Pp
The
.Nm
driver will reject attempts to
.Tn DMA
to buffers not aligned to the required boundary.
The
.Xr wd 4
disk driver will back off to
.Tn PIO
mode to accomplish these transfer requests, at reduced system performance.