Acorn Risc Technologies StrongARM CD-ROM/Acorn Risc Technologies StrongARM CD-ROM.iso/ftp/documents/appnotes/216_230/223c/Text

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24th October 1995
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Support Group Application Note
Number: 223
Issue: 1.0
Author: DW
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Connection of Multiple Hard Discs to 32 Bit Acorn Machines
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Notes:
This document describes the procedures required to connect second and (where
possible) subsequent hard discs to Acorn systems. The properties and
restrictions of the available drive buses are discussed, and details of
drive compatibility and some appropriate link settings are provided.
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Applicable Hardware:
All 32-bit Acorn systems

Related Application Notes:
273: CD ROM Drives and their Handling under RISC OS Explained

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Copyright (C) 1995 Acorn Computers Limited

Every effort has been made to ensure that the information in this leaflet is
true and correct at the time of printing. However, the products described in
this leaflet are subject to continuous development and improvements and
Acorn Computers Limited reserves the right to change its specifications at
any time. Acorn Computers Limited cannot accept liability for any loss or
damage arising from the use of any information or particulars in this
leaflet. ACORN, ECONET and ARCHIMEDES are trademarks of Acorn Computers
Limited.
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Support Group
Acorn Computers Limited
Acorn House
Vision Park
Histon
Cambridge
CB4 4AE
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Introduction

With the exceptions of the Archimedes 300 series, the R225, the A3000 and
the A3010, all 32-bit Acorn systems have been supplied either with a hard
drive as standard or with a built-in interface to allow a hard drive to be
added as a user upgrade. As users write or acquire more software and their
first hard drive begins to reach capacity, many consider the option of
adding further drives to increase their system's available random-access
storage. This document details how this may be done, and what the
limitations imposed by each of the possible upgrade routes are.

Since the launch of the Archimedes range in 1987, Acorn have produced
systems containing one of three types of hard disc interface. These are:

ST506:
This interface was standard on the Archimedes 440, 400/1 series and R140.
ST506 allows a maximum of two devices to be linked together on the same
ST506 interface. ST506 has been almost entirely superseded by other drive
standards, and as such ST506 drives are now extremely difficult to obtain.

SCSI:
This interface was standard on the Archimedes 540 and R260. SCSI interfaces
can still be added as an Acorn standard ugrade to systems capable of taking
full-size (A5000-style) expansion cards; all you need to do is fit an
appropriate SCSI interface, such as Acorn's own AKA32. Third parties also
producs SCSI interfaces for systems which accept A3000-style expansion
cards. Up to seven drives may be daisychained on a SCSI bus, although
restrictions in some versions of the SCSIFS module may only allow up to four
drives or partitions to display their icons on a RISC OS icon bar. SCSI has
been a widely recognised drive standard on high-performance systems for many
years, and is enhanced SCSI variants may continue to be so for many more;
SCSI drives are widely available, and SCSI tends to be used to interface the
highest storage capacity drives. SCSI drives of up to 9 Gb capacity are
currently available.

IDE:
This interface is standard on the A3020, A4000, A5000, A7000 and Risc PC.
The interface is present on the floppy-only version of the A3020, even
though it is not used. Up to two drives can be linked together on the same
IDE interface. IDE is rapidly becoming the drive interface standard for low
and medium performance-range desktop systems, and IDE drives of up to 2 Gb
capacity are currently available.

Drive capacity and mapping

Production releases of the FileCore module prior to 2.91 (as shipped with
RISC OS 3.6) are only capable of addressing filesystems of size <=512 Mb.
This means that, without the use of partitioning software, only drives of
formatted size <=512 Mb may be added. Larger drives than this will require
partitioning using third party software. Formatting of ST506 and IDE drives
can be handled by !HForm, supplied with all machines; SCSI drives cn be
handled by either SCSIDM (for the Acorn card; third parties will have
different software) or the new (RISC OS 3.6) version of !HForm. This new
!HForm will also cater for >512Mb contiguous partitions on large drives.

For earlier iterations of FileCore, a soft-loadable version for use with
RISC OS 3.5 is in testing.

CD ROM bus support capability

In addition to hard drives, it is often possible to connect other
peripherals to these drive buses; CD ROMs are the most common peripheral to
connect in this manner.

ST506:
No CD ROM drives have been produced with an ST506 interface.

SCSI:
It is possible to add CD ROM drives onto an existing SCSI chain; the same
procedure used to attach hard discs is used for CD ROM drives, and the same
interfacing standards must be complied with. When adding a CD ROM drive,
make sure that no hard drives have higher-numbered SCSI IDs than it. The CD
ROM drives currently supported by Acorn-originated drivers are:

Sony CDU6111, CDU6211, CDU541, CDU561
Philips CM131, CM231
Toshiba XM2200A, 3301
Hitachi CDR1650S, CDR1750S
Chinon CDS-431

Drivers for other models of CD ROM drive are available from assorted third
parties, such as Cumana and Alsystems; see Appendix A.

IDE:
A CD ROM drive may be added to an IDE bus as the slave device; however, not
all drives are guaranteed to work with the combination of bus controller and
mastering hard drive shipped as standard. Currently, IDE CD ROM drives have
only been tested with the Risc PC (which uses a 37C665 controller) and the
Conner CFS210A, CFS420A, CFS425A and CFS850A hard drives which are fitted to
the different versions thereof; the Panasonic CR562B is an appropriate drive
to install on a RISC OS 3.5 system, and the Sony CD50E ATAPI unit is known
to work on a RISC OS 3.6 machine (the latter contains the CDFSSoftATAPI
driver in ROM)

Adding a Second ST506 Drive

In all cases, the user will be required to change the status of links on the
drives to enable them to operate together; details of link configuration
should be supplied with the additional drive.

Archimedes 400/1
Approximately halfway up the left hand side of the PCB (facing from front to
rear of the machine; note that the backplane will need to be removed before
a clear view of the sockets can be obtained) are three sockets labelled SK8,
SK10 and SK11. SK10 is a 20 way socket to which the first DATA cable
connects; the other end of this cable is connected to the first hard drive.
SK8 is a second 20 way socket which can be used to run a separate DATA cable
to a second hard drive. SK11 is a 34 way socket to which the CONTROL cable
connects; the 34 way CONTROL cable should be daisychained to run to both the
internal and external Hard Discs. The interface is normally configured to
support up to eight heads per drive; by changing both LK12 and LK13 from
their default positions to their alternative positions, up to 16 heads can
be supported. This action removes the reduced write current capability
provided by the interface, but this tends not to be used externally by
larger capacity Hard Disc units.

Archimedes 440 / R140
Much of the information required for the pre June 1989 440 systems is
identical to the 400/1 system upgrade. The differences lie in the cable
sockets and the link numbers. The two sockets used for connecting the first
hard drive are SK10 for the CONTROL cable and SK9 for the DATA cable. The
DATA cable for the second drive attaches to socket SK8.

The two links which require altering to enable dual drive support are LK3
and LK4; LK3 should be set EAST and LK4 should be set WEST.  The other
details regarding the daisychaining of the CONTROL cable are the same as
above.

<Insert Fig1>

Figure 1: ST506 Drive Connections

Drive compatibility
The interface type supplied by Acorn is ST506 MFM (Modified Frequency
Modulation). Drives designated as RLL will work, although it will not be
possible to use the full storage capacity of the drive; as a rule of thumb,
it is generally possible to map up to 66% of the design capacity of an RLL
unit.

Drives to be attached should have an access time of 28ms, no more that 1024
cylinders and no more than 16 heads.

Termination
A very important point to note, and one which is often forgotten, is that
only the second drive (at the end of the data cable) in a two-drive system
should be terminated. On examination of the PCB on the first drive, it is
possible to find one or more terminating resistor packs; these are usually
sited close to the data cable connector, and may resemble either a small
resin-encased SIPP chip or a DIL package. Usually the terminator packs are
brightly coloured to aid identification, and invariably they are socketed
rather than soldered. Once the fitting positions (and orientations, in the
case of DIL packages) of the terminators on the first drive have been noted,
they should be removed.

A Note on Drive Availability
The popularity of the ST506 interface standard was beginning to wane by
1990; when IDE appeared, this decline was accelerated. Today, ST506 drives
are very difficult to obtain; unless a user already has an ST506 drive to
hand, it is more advisable to add a second drive interface conforming to a
more current standard and then fit an appropriate drive to it rather than
attempt to procure an ST506 drive.

Adding Second and Successive SCSI Drives

Probably the most flexible, and certainly the most expandable, drive
interface bus for Acorn systems is SCSI. A SCSI bus supports a maximum of 8
devices, numbered 0 through 7; however, drives and other peripherals can
only be used as devices 0 through 6, as device 7 is reserved for the "host
adaptor," otherwise known as the SCSI interface card. A properly-designed
SCSI device chain should appear to be a continuous "run" of cable, with a
terminator at each end. Cable spurs (between the main backbone of cable and
the connector on the back of the drive) should not exceed 100mm in length.
The backbone cable should be 50 way twisted pair or IDC ribbon, with between
80 and 90 ohm impedance.

When adding drives to an Acorn SCSI interface, you should make sure:

• that all drives are compatible with the ANSI X3.131 - 1986 SCSI Standard,
  and with the guidelines in document CCS X3T9.2/85-52 Revision 4B

• that the drives are numbered sequentially, with numbering starting from 0

• that no CD ROM drives have SCSI ID numbers lower than numbers assigned to
  hard discs

Termination
The SCSI interface is open collector, and hence termination is required at
both ends of the bus to pull all the signal and control lines up to the
appropriate level (typically 2-3V). A terminator pack should be fitted to
the device closest to each end of the SCSI cable; termination should be
disabled on devices between these. On more modern SCSI drives, termination
can often be disabled by changing the status of a jumper rather than by
physically removing socketed termination packs; check the device
documentation, or consult the device manufacturer, for further details on
how this may be done.

Adding a Second IDE Drive

In common with the ST506 interface, IDE supports a maximum of two drives per
bus. However, rather than having separate control and data cables, IDE
relies on some signal arbitration taking place between the two drives on the
bus; thus the drives must be configured in a "Master / Slave" arrangement.
The length of IDE cables, in addition to the spur length (spur length should
be kept to <20mm), is critical; the cable distance between adjacent devices
on an IDE bus should be kept to between 200 and 250mm, and should definitely
not exceed 300mm.

Master or Slave?
Some drive arrangements only work "one way," that is with a given drive as
the master and a second given drive as the slave, but not the other way
round. If you find a configuration which does not appear to work, first try
swapping the cable position and designation of the drives. The table below
details the configurations and link settings of the drives we have tested
and know to work together:

<Insert Table1>

Table 1: Known working IDE Drive Configurations

Compatibility Issues
As it currently stands, the IDE specification is not as rigidly defined as
the SCSI standard, particularly in the area of timings and their tolerances.
Thus it is possible to take two drives and a controller, all of which are
compliant with the IDE specification, attach them together on an IDE bus and
have sufficient disparity between component timings that the system hangs.
Alternatively, some drive combinations can cause one of the drives to
"forget"any data (including formatting information) which has previously
been saved to it if it is switched off and back on again.

Acorn has only tested the drives listed in the above table, however these
are known to work correctly together on both A5000 and Risc PC systems.

If you are planning to make use of a drive which is not listed in the table,
there are a few things to pay particular attention to:

* Drive speed - Some drives have slow I/O timings which will work on a
  machine such as an A3020, which has slower cycle times. A faster Acorn
  machine such as a Risc PC might have trouble.

* IRQ issues - Some drives have a pull-up resistor on the IRQ line.  This is
  not a good idea - the IRQ line on IDE drives is a tri-state output, and is
  active high. So disabling the IRQ output on the drive can cause an
  erroneous IRQ.

* Drive selection - Some IDE drives support selection of the drive via a
  signal on the IDE connector - the jumper which enables this is the Cable
  Select, and is often marked as CS on the drive.  The Risc PC does not
  support Cable Select, therefore connecting a drive with this enabled will
  not work. Similarly, Spindle Sync must be disabled.

Multiple Interfaces on One Machine

Where one flavour of disc interface is already fitted to a machine, either
on the motherboard or via an expansion card, there is ordinarily no problem
in connecting another interface in the form of an expansion card, if
available expansion card space allows. The only exception to this is the
Acorn SCSI card; RISC OS will only allow one Acorn SCSI interface to be
installed in a machine, although RISC iX is capable of differentiating
between them. If it is necessary to connect more than six hard drives and /
or CD ROM drives, SCSI cards are available from Cumana and Alsystems which
allow more than one card to be fitted to a single machine (physical space
permitting).

Troubleshooting

Occasionally, such as when power is interrupted during a write operation to
a hard disc, disc errors occur. Some error codes are:

From the ST506 Hard Disc controller:

&01    ABT Command abort has been accepted
&02    IVC Invalid command
&03    PER Command parameter error
&04    NIN Head positioning, disc access or drive check command before SPC has
           been issued
&05    RTS TST command after SPC command
&06    NUS USELD for a selected drive has not been returned
&07    WFL Write fault (WFLT) detected on the ST506 interface
&08    NRY Ready signal has been negated
&09    NSC Seek complete (SCP)was not returned before timeout
&0A    ISE SEK or disc access command issued during a seek
&0B    INC Next cylinder address greater than number of cylinders
&0C    ISR Invalid step rate; highest-speed seek specified in normal seek mode
&0D    SKE SEK or disc access command issued to drive with seek error
&0E    OVR Data overrun (memory running slower than drive)
&0F    IPH Head address greater than number of heads
&10    DEE Error Correction Code (ECC) detected an error
&11    DCE CRC error in data area
&12    ECR ECC corrected an error
&13    DFE Fatal ECC error in data area
&14    NHT In CMPD command data mismatched from host and disc
&15    ICE CRC error in ID field (not generated for ST506)
&16    TOV ID not found within timeout
&17    NIA ID area started with an improper address mark
&18    NDA Missing address mark
&19    NWR Device write-protected

Errors &01, &03, &04 and &05 should be trapped by ADFS, and hence should
never be seen by the user.

From the IDE Hard Disc controller:

&02    IVC Command aborted by controller
&07    WFL Write fault
&08    NRY Drive not ready
&09    NSC Track 0 not found
&13    DFE Uncorrected data error
&16    TOV Sector ID field not found
&17    NIA Bad block mark detected
&18    NDA No data address mark
&20        No DRQ when expected
&21        Drive busy when commanded
&22        Drive busy on command completion
&23        Controller did not respond within timeout
&24        Unknown code in error register

From these tables, it is clear that some errors relate to the data on the
disc and others to the drive itself; if you see an error other than &13,
&16, &17 or &18 from the hard drive, you should refer the problem to your
Acorn dealer.

The integrity of the data structures on a disc can be tested by using the
*CHECKMAP command; this searches through the directory structure of a disc
and compares it to the record of the structure as stored in the directory
headers.

If you find that you have any inconsistencies with your data, several
products exist which are able to recover as much data as possible from a
damaged disc; one of the popular packages is "Archimedes Disc Rescue,"
available from LookSystems.

Other Standards

In addition to ST506, SCSI and IDE, other drive standards have been
developed as extensions and enhancements; in particular, SCSI 2, SCSI 2
Wide, SCSI 2 Fast and EIDE. SCSI 2 protocols are designed to be backwardly
compatible with SCSI protocols; many SCSI 2 drives have a link which can be
set to enable or disable the variants of SCSI 2, while others can make the
translation automatically.Consult the documentation supplied with the drive,
or the drive manufacturer, as appropriate refarding compatibility.

EIDE is an enhanced version of IDE designed primarily to handle drives of
capacity >2 Gb. Currently EIDE is not supported on our platforms.

Appendix A: Useful Addresses

Disclaimer:
The inclusion or omission of an address does not imply any endorsement of
that company or product by Acorn Computers Ltd.

For SCSI and SCSI 2 interfaces

Cumana Ltd
Pines Trading Estate
Broad Street
Guildford
Surrey
GU3 3BH

Tel: [phone]
Fax: [phone]

Alsystems
47 Winchester Road
Four Marks
Alton
Hants
GU34 5HG

Tel: [phone]

For IDE interface expansion cards

HCCS Associates Ltd
575-583 Durham Road
Low Fell
Gateshead
Tyne & Wear
NE9 5JJ

Tel: [phone]
Fax: [phone]

ICS (Ian Copestake Limited)
1 Kington Road
Wirral
Merseyside
L48 5ET

Tel: [phone]
Fax: [phone]



Beebug Ltd
117 Hatfield Road
St Albans
Hertfordshire
AL1 4JS

Tel: [phone]
Fax: [phone]

For data recovery software and services:
LookSystems
47 Goodhale Road
Bowthorpe
Norwich
Norfolk
NR5 9AY

Tel: [phone]