186 lines
6.0 KiB
Groff
186 lines
6.0 KiB
Groff
.\"
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.\" Copyright (c) 1995, 1996, 1997
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.\" Justin T. Gibbs. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software withough specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $Id: ahc.4,v 1.11 1998/06/08 06:11:58 jkoshy Exp $
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.\"
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.Dd April 20, 1996
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.Dt AHC 4 i386
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.Os FreeBSD
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.Sh NAME
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.Nm ahc
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.Nd Adaptec VL/EISA/PCI SCSI host adapter driver
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.Sh SYNOPSIS
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For one or more VL/EISA cards:
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.Cd controller eisa0
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.Cd controller ahc0
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.Pp
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For one or more PCI cards:
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.Cd controller pci0
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.Cd controller ahc0
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.Pp
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To enable SCB paging:
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.Cd options AHC_SCBPAGING_ENABLE
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.Pp
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To enable tagged queueing:
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.Cd options AHC_TAGENABLE
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.Pp
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To allow PCI adapters to use memory mapped I/O if enabled:
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.Cd options AHC_ALLOW_MEMIO
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.Pp
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For one or more SCSI busses:
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.Cd controller scbus0 at ahc0
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.Sh DESCRIPTION
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This driver provides access to the
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.Tn SCSI
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bus(es) connected to Adaptec
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274x, 284x, 2940, 3940, or controllers based on the
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.Tn AIC7770,
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.Tn AIC7850,
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.Tn AIC7860,
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.Tn AIC7870,
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or
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.Tn AIC7880
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host adapter chips.
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Features include support for twin and wide busses,
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ultra
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.Tn SCSI,
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two active commands at a time per non-tagged queueing target,
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tagged queuing,
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and SCB paging.
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.Pp
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The number of concurrent transactions allowed is chip dependent
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and ranges from 3 to 16.
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On PCI adapters,
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this number can be increased with the SCB paging option.
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SCB paging implements an algorithm to 'page-out' transactions
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that are in the disconnected state so that the freed space in
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the controller's memory can be used to start additional transactions.
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On the aic7880 and aic7870,
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this increases the maximum number of outstanding transactions from 16 to 255.
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On the aic7850 and aic7860 controllers, this maximum rises from 3 to 8.
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During the hardware probe,
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a diagnostic showing the ratio of hardware supported 'slots' to number
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of transactions is printed.
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SCB paging is enabled with the
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.Dq Dv AHC_SCBPAGING_ENABLE
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configuration option.
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This option will likely be removed and become the default behavior for
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adapters that support it,
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in the near future.
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.Pp
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Tagged queueing is enabled with the
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.Dq Dv AHC_TAGENABLE
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configuration option.
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Tagged queueing allows multiple transactions to be queued at the device
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level instead of the host level,
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allowing the device to re-order I/O to minimize seeks,
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seek distance,
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and to increase throughput.
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Tagged queueing can have a significant impact on performance for seek
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bound applications and should be enabled for most configurations.
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Unfortunately, some devices that claim to support tagged queueing fail
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miserably when it is used.
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The only reason tagged queueing remains as a controller option is as a
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stop gap measure until a mechanism to detect these broken devices and to
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control this feature on a per device basis is in place.
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.Pp
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Memory mapped I/O can be enabled with the
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.Dq Dv AHC_ALLOW_MEMIO
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configuration option.
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Memory mapped I/O is more efficient than the alternative, programmed I/O.
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Most PCI BIOSes will map devices so that either technique for communicating
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with the card is available.
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In some cases,
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usually when the PCI device is sitting behind a PCI->PCI bridge,
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the BIOS fails to properly initialize the chip for memory mapped I/O.
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The symptom of this problem is usually a system hang if memory mapped I/O
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is attempted.
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Most modern motherboards perform the initialization correctly and work fine
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with this option enabled.
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.Pp
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Per target configuration performed in the
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.Tn SCSI-Select
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menu, accessible at boot
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in
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.No non- Ns Tn EISA
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models,
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or through an
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.Tn EISA
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configuration utility for
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.Tn EISA
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models,
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is honored by this driver with the stipulation that the
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.Tn BIOS
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must be enabled for
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.Tn EISA
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adaptors. This includes synchronous/asynchronous transfers,
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maximum synchronous negotiation rate,
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disconnection,
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and the host adapter's SCSI ID.
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.Pp
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Note that I/O addresses are determined automatically by the probe routines,
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but care should be taken when using a 284x
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.Pq Tn VESA No local bus controller
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in an
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.Tn EISA
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system. Ensure that the jumpers setting the I/O area for the 284x match the
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.Tn EISA
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slot into which the card is inserted to prevent conflicts with other
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.Tn EISA
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cards.
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.Sh BUGS
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Some Quantum drives (at least the Empire 2100 and 1080s) will not run on an
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.Tn AIC7870
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Rev B in synchronous mode at 10MHz. Controllers with this problem have a
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42 MHz clock crystal on them and run slightly above 10MHz. This causes the
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drive much confusion. Setting a maximum synchronous negotiation rate of 8MHz
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in the
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.Tn SCSI-Select
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utility
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will allow normal function.
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.Sh SEE ALSO
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.Xr aha 4 ,
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.Xr ahb 4 ,
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.Xr cd 4 ,
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.Xr scsi 4 ,
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.Xr sd 4 ,
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.Xr st 4
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.Sh AUTHORS
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The
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.Nm
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driver was written by
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.An Justin Gibbs .
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The
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.Tn AIC7xxx
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sequencer-code assembler was
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written by
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.An John Aycock .
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.Sh HISTORY
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The
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.Nm
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driver appeared in
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.Fx 2.1 .
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