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UDMA information for kernels 2.0.35+

Version 0.4 - July 98

by Andrew D. Balsa 

If you are in a hurry, skip to the "How does one use UDMA support?" section.

If you need troubleshooting advice, check the "Unreliable drive +

motherboard + driver combination" section.

Support for UDMA is based on previous work by Kim-Hoe Pang and Christian

Brunner, posted on the Linux Kernel mailing list around September 1997.

Additional code was provided by Michel Aubry (VIA support) and Andre Hedrick

(support for various PCI UDMA controller cards). The code base is Mark

Lord's triton.c driver.

Check the Linux UDMA mini-HOWTO by Brion Vibber first! It is the only Linux

specific document available on the subject.

Technical references:

a) The Intel 82371AB data sheet, available in PDF format.

b) The SiS 5598 and 5591 data sheets, available in Microsoft Word format. :(

c) The VIA 82C586, 82C586A and 82C586B data sheets, in PDF format.

d) Small Form Factor document SFF 8038I v1.0. This is the original document

   that describes the DMA mode 2 protocol. Available in PDF format.

e) The ATA/ATAPI-4 Working Draft, revision 17. This is document

   d1153r17.pdf (in PDF format), available from the main IDE technical

   reference site, ftp://fission.dt.wdc.com/pub/standards. This draft

   describes the Ultra DMA protocol and timings.

A somewhat less technical, but still very informative document is the

Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan. Check

the Web page at http://come.to/eide.

**************************************************************************

Files changed

-------------

Here is the set of files from Linux kernels 2.0.32/2.0.34 modified to enable

UDMA transfers on motherboard chipsets that support it. For each file, there

is a small explanation of the changes.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

The following changes do not affect performance or stability of the IDE

driver in any way.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

/drivers/block/triton.c

 - removed some Intel specific timing stuff. This should not affect

driver operation or performance. This is the only file that is heavily

modified; the Promise and Artop code is by Andre Hedrick, the VIA code

by Michel Aubry.

/drivers/block/ide.c

 - added UDMA drive reporting during driver initialization, at the end

of routine do_identify (single line mod).

 - added data for SiS 5513 and VIA VP-1 chipset in routine probe_for_hwifs

(single line mods). Each new UDMA capable chipset will have to be added to

this list (a single line is needed each time). Notice that you don't even

need the motherboard chipset's data sheets to find the needed information.

You just have to identify the IDE controller. You can do this by checking

/proc/pci, and then comparing the IDE controller signature with that

available from the Linux kernel.

As it stands in this patched version, routine probe_for_hwifs supports the

following chipsets: Intel FX, HX, VX, TX, LX and SiS 5513 (which is

integrated in the SiS 5571, 5598 and 5591 chips). The VIA-VP1

chipset is supported for DMA mode 2 transfers, but compatibility has not

been tested with this driver. The VIA MVP-3 is reported OK with UDMA.

/drivers/block/ide.h

 - added flag using_udma in struct ide_drive_s (single line mod).

Small changes to the tape and ide-floppy code, and additions to pci.h and

pci.c for the extra PCI UDMA controller devices.

Tested configurations

---------------------

UDMA support has been thoroughly tested on the following configurations:

Intel TX motherboard, PCI bus at 33 and 37.5MHz. (ASUS TX-97E)

SiS 5598 motherboards, PCI bus at 33 and 37.5MHz. (Chaintech P5-SDA; ASUS

SP-97V at 33MHz only)

IBM DeskStar 6.4Gb and 8.4Gb drives. Samsung UDMA hard disk proved

unreliable under Linux _and_ Windows95 (so it was not a driver problem).

Other UDMA drives not tested.

libc5 and gcc2.7.2. Also tested under libc6 (RedHat 5.0).

6x86MX processor running at 166MHz or 187.5MHz.

DANGER: EIDE drives do not accept a PCI bus at 41.5MHz (83MHz / 2). Trying

to run DMA Mode 2 or UDMA at these PCI bus clocks will result in crashes and

loss of data. If your FSB runs at > 75MHz you MUST set the PCI bus for

asynchronous 33MHz operation. YOU HAVE BEEN WARNED.

Andre Hedrick Tests [IMPORTANT: those are SMP configurations]

-------------------------------------------------------------

Test I

------

Tyan Tomcat III bios v4.01 SMP Dual P5 200 w/ Artop AEC6210 w/ DMA2 drives

Intel MultiProcessor Specification v1.4

    Virtual Wire compatibility mode.

OEM ID: OEM00000 Product ID: PROD00000000 APIC at: 0xFEE00000

Processor #0 Pentium(tm) APIC version 17

Processor #1 Pentium(tm) APIC version 17

I/O APIC #2 Version 17 at 0xFEC00000.

Processors: 2

Linux version 2.0.34 (root@Zosma) (gcc version 2.8.1) #1 Mon Jun 8 16:40:25 CDT

Booting processor 1 stack 00002000: Calibrating delay loop.. ok - 79.67

BogoMIPSTotal of 2 processors activated (159.33 BogoMIPS).

Starting kswapd v 1.4.2.2

ide: DMA Bus Mastering IDE controller on PCI bus 0 function 57

ide: ports are not enabled (BIOS)

ide: AEC6210 ROM enabled but no address

ide: UDMA Bus Mastering IDE controller on PCI bus 0 function 160

ide: timings == 04010401

    ide0: BM-DMA at 0x6700-0x6707

    ide1: BM-DMA at 0x6708-0x670f

hda: Maxtor 72004 AP, 1916MB w/128kB Cache, CHS=973/64/63, DMA

hdb: Maxtor 71626 A, 1554MB w/64kB Cache, CHS=789/64/63, DMA

hdc: IOMEGA ZIP 100 ATAPI, ATAPI FLOPPY drive

hdd: HP COLORADO 5GB, ATAPI TAPE drive

ide-tape: Sorry, DRQ types other than Accelerated DRQ

ide-tape: are still not supported by the driver

ide-tape: the tape is not supported by this version of the driver

ide2: ports already in use, skipping probe

ide0 at 0x6300-0x6307,0x6402 on irq 11

ide1 at 0x6500-0x6507,0x6602 on irq 11 (shared with ide0)

scsi0 : ncr53c8xx - revision 2.5f.1

Test II

-------

SuperMicro P6DNF SMP Dual P6 233 w/ Artop AEC6210 and Promise Ultra33

Intel MultiProcessor Specification v1.4

    Virtual Wire compatibility mode.

OEM ID: INTEL    Product ID: 440FX        APIC at: 0xFEE00000

Processor #0 Pentium(tm) Pro APIC version 17

Processor #1 Pentium(tm) Pro APIC version 17

I/O APIC #2 Version 17 at 0xFEC00000.

Processors: 2

Linux version 2.0.34 (root@Orion) (gcc version 2.8.1) #1 Wed Jun 17 01:13:15 CDT 1998

Booting processor 1 stack 00002000: Calibrating delay loop.. ok - 232.65 BogoMIPS

Total of 2 processors activated (464.49 BogoMIPS).

ide: Intel 82371 (single FIFO) DMA Bus Mastering IDE

    Controller on PCI bus 0 function 57

ide: ports are not enabled (BIOS)

ide: AEC6210 ROM enabled at 0xfebf8000

ide: PCI UDMA Bus Mastering IDE

    Controller on PCI bus 0 function 160

ide: timings == 04010401

    ide0: BM-DMA at 0xef90-0xef97

    ide1: BM-DMA at 0xef98-0xef9f

hda: QUANTUM FIREBALL ST3.2A, 3079MB w/81kB Cache, CHS=782/128/63, UDMA

hdb: QUANTUM FIREBALL ST6.4A, 6149MB w/81kB Cache, CHS=784/255/63, UDMA

hdc: IOMEGA ZIP 100 ATAPI, ATAPI FLOPPY drive

hdd: CD-ROM CDU611, ATAPI CDROM drive

ide2: ports already in use, skipping probe

ide0 at 0xeff0-0xeff7,0xefe6 on irq 10

ide1 at 0xefa8-0xefaf,0xefe2 on irq 10 (shared with ide0)

Test III

--------

Same kernel above but with Promise Ultra33

ide: Intel 82371 (single FIFO) DMA Bus Mastering IDE

    Controller on PCI bus 0 function 57

ide: ports are not enabled (BIOS)

ide: PDC20246 ROM enabled at 0xfebd0000

ide: PCI UDMA Bus Mastering IDE

    Controller on PCI bus 0 function 160

ide: timings == 000003ee

    ide0: BM-DMA at 0xef80-0xef87

    ide1: BM-DMA at 0xef88-0xef8f

hda: QUANTUM FIREBALL ST3.2A, 3079MB w/81kB Cache, CHS=782/128/63, UDMA

hdb: QUANTUM FIREBALL ST6.4A, 6149MB w/81kB Cache, CHS=784/255/63, UDMA

hdc: IOMEGA ZIP 100 ATAPI, ATAPI FLOPPY drive

hdd: CD-ROM CDU611, ATAPI CDROM drive

ide2: ports already in use, skipping probe

ide0 at 0xeff0-0xeff7,0xefe6 on irq 10

ide1 at 0xefa8-0xefaf,0xebe6 on irq 10 (shared with ide0)

All tests cases yield this problem, IOMEGA ZIP 100 ATAPI FW 23.D

I have a patch fix for 2.1.99->106 similar for FW 21.D drives.

ide-floppy: hdc: I/O error, pc = 5a, key =  5, asc = 24, ascq =  0

ide-floppy: Can't get drive capabilities

Note that both AEC6210 and PDC20246 have onboard bios that auto-config.

What UDMA support does

----------------------

        - It enables UDMA transfers on the Intel TX chipset.

        - It enables DMA mode2 transfers on the SiS 5571 and VIA VP-1

          (82C586) chipsets.

        - It enables DMA mode2 and UDMA mode2 transfers on the SiS 5598 and

          SiS 5591 chipsets, and the VIA VP3 and MVP-3.

        - With single line mods for each new chipset, it will support any DMA

          mode2 and/or UDMA capable chipset compatible with document

          SFF 8038I v1.0.

        - Supports a variety of PCI UDMA controller cards.

Support for other chipsets

--------------------------

It is relatively easy to add support for other chipsets. Some chipsets are

entirely integrated (e.g. the SiS 5598 chipset has various devices in a

single chip), others are divided into a Northbridge (CPU to PCI circuitry,

L2 cache control, etc) and Southbridge (PCI to IDE bus mastering interface,

USB, etc). We are dealing here with the Southbridge, specifically with the

IDE bus master PCI device. If the data sheet says the device is SFF 8038I

v1.0 compatible, then the registers have a more or less standard layout and

this driver should work with the below changes:

1) Check that the chipset is correctly identified by /proc/pci. Search for

the line that identifies a bus-mastering IDE controller device.

2) If the chipset is not correctly identified (new chipsets are not in

kernels up to 2.0.33), you will need to edit /include/linux/pci.h and

/drivers/pci/pci.c. This is actually quite easy, requiring a single line in

each of these files.

3) Now add a single line to ide.c, in routine probe_for_hwifs.

4) Test and report results; when troubleshooting, please check first that

you have the latest BIOS for your motherboard.

HOW does UDMA mode2 work?

-------------------------

Well, actually, the excellent triton.c driver written by Mark Lord is a

generic DMA transfer hard disk driver. It does not depend on any chipset

feature or transfer mode (i.e. it will work with DMA mode 2, UDMA and other

future DMA modes with little or no changes). BTW in late 2.1.x kernels the

driver was renamed ide-dma.c, to indicate that it is independent of the

chipset used.

(Note: triton is the "old" name for the Intel FX chipset, for which Mark

Lord wrote the driver initially.)

The Intel chipset specific parts were slightly changed in the triton.c

driver. These are only used to gather information for driver testing, and

actually do not affect the operation or performance of the driver, so the

changes are (well, should be) relatively inocuous.

The real work involved in setting up the chips for DMA transfers is done

mostly by the BIOS of each motherboard. Now of course one hopes that the

BIOS has been correctly programmed...

For example, the ASUS SP-97V motherboard with its original BIOS (Rev. 1.03)

would malfunction with the modified Linux driver in both DMA mode 2 and UDMA

modes; it would work well using PIO mode 4, or under Windows 95 in all

modes. I downloaded the latest BIOS image (Rev. 1.06) from the ASUS Web site

and flashed the BIOS EPROM with the latest BIOS revision. It has been

working perfectly ever since (at 66 MHz bus speeds).

What this tells us is that the BIOS sets up the DMA controller with specific

timing parameters (active pulse and recovery clock cycles). My initial BIOS

revision probably had bad timings. Since the Windows 95 driver sets up those

timings by itself (i.e. it does not depend on the BIOS to setup the hard

disk controller timing parameters), I initially had problems only with the

Linux driver, while Windows 95 worked well.

So, let me state this again: this Linux (U)DMA driver depends on the BIOS for

correct (U)DMA controller setup. If you have problems, first check that you

have the latest BIOS revision for your specific motherboard.

OTOH Michel Aubry's code for the VIA Apollo chipset has complete support for

setting up the timing parameters. Check the triton.c source code for

details.

New BIOS revisions can be downloaded from your motherboard manufacturer's

Web site. Flashing a new BIOS image is a simple operation but one must

strictly follow the steps explained on the motherboard manual.

Late Award BIOS revisions seem stable with respect to UDMA. Anything with a

date of 1998 should be fine.

Features missing from the present UDMA support code

---------------------------------------------------

It does not set UDMA transfer parameters (the driver assumes the BIOS has

correctly setup all timing parameters) in the various chipsets. This

requires access to a complete set of data sheets for the various chipsets,

and testing on a variety of configurations, so it's not exactly within the

reach of a humble Linux hacker. IMHO this is best left to the guys at Award

and AMI (the BIOS guys), and to the motherboard engineers.

Basically, UDMA transfers depend on two timing parameters:

        1) The pulse width of the active strobe signal for data transfers

(usually described as the active pulse width).

        2) The delay between the negation of the DMA READY signal to the

assertion of STOP when the IDE controller wants to stop a read operation

(usually described as the recovery time).

Both timing parameters can be set individually for each hard disk (up to two

hard disks per channel).

Knowing which registers must hold this data and the appropriate values, one

could program the Linux triton.c driver to setup the IDE controller device,

without relying on BIOS settings. However, some chipsets allow setting other

timing parameters, and the required code would quickly increase to a

not-so-easy-to-manage size. Better keep it simple, IMHO.

It seems Mark Lord has devised a neat way to do this in the ide-dma driver

included in late kernels 2.1.x: each chipset has an entry in a table, with

safe timing values. The chipset is also identified when the driver is

loaded.

How does one use UDMA support?

------------------------------

1) Backup your data or you will be sorry. Now do "hdparm -t -T

/dev/hda". Write a small note with the transfer rates you see.

2) Reboot. Press [Del] to launch the CMOS SETUP routine, go to the

CHIPSET SPECIFIC or PERIPHERALS SETUP menus, and enable UDMA transfers

for your hard disk drives which are UDMA capable, or leave the fields in

the default "AUTO" value. Enable both IDE channels even if you have just

one IDE drive (default setting).

3) Boot Linux, compile the kernel with the TRITON support enabled. Install

the new kernel (the lilo thingy). Reboot Linux.

4) Watch for the drive parameters message when the kernel loads (or type

"dmesg | more" after login). After the Cyl, Heads, Sect parameters you

should see "DMA" or "UDMA" depending on your hard disk drive and chipset

capabilities.

Here is what I get with UDMA enabled in the BIOS of my SiS 5598 based

configuration, with an IBM UDMA capable hard disk as hda:

...

ide: DMA Bus Mastering IDE controller on PCI bus 0 function 9

    ide0: BM-DMA at 0x4000-0x4007

    ide1: BM-DMA at 0x4008-0x400f

hda: IBM-DHEA-36480, 6197MB w/476kB Cache, LBA, CHS=790/255/63, UDMA

...

If I disable UDMA in the BIOS, I get:

...

ide: DMA Bus Mastering IDE controller on PCI bus 0 function 9

    ide0: BM-DMA at 0x4000-0x4007

    ide1: BM-DMA at 0x4008-0x400f

hda: IBM-DHEA-36480, 6197MB w/476kB Cache, LBA, CHS=790/255/63, DMA

...

5) Again, do "hdparm -t -T /dev/hda". Smile. Test your setup by copying

a few large files around or doing some large compilation (e.g. the Linux

kernel itself).

Performance issues

------------------

1) Sustained transfer rates.

Here is some data gathered after extensive testing, using the hdparm utility

(also written by Mark Lord):

PIO mode 4 transfer rates under Linux:   +/- 5.2MB/s

DMA mode 2 transfer rates under Linux:   +/- 7.2MB/s

UDMA mode 2 transfer rates under Linux:  +/- 9.8MB/s

Data gathered on a Chaintech SiS 5598 motherboard, 6x86MX @ 187.5MHz, Linux

2.0.32/2.0.33 with patched triton.c driver as explained above, IBM DeskStar

6.4GB hard disk (IBM-DHEA-36480).

The integrated video hardware in the SiS 5598 chip was disabled (a standard

PCI video board was used); enabling the integrated SVGA controller will

cause a 20% performance hit in processing performance, due to limited main

memory bandwidth.

The TX motherboard under the same test conditions will be slightly

slower (0.1 - 0.2 MB/s slower).

Burst (instantaneous) transfer rates are supposed to go from 16.6MB/s (PIO

mode 4) to 16.6MB/s (DMA mode 2) up to 33MB/s (UDMA). In his patch against

kernel 2.1.55, Kim-Hoe Pang actually checked the UDMA burst transfer rate

with a logic analiser: 60ns/word, which translates into 33MB/s.

Note that burst transfer rates only affect data transfers to/from the EIDE

drive cache (476kB for the IBM 6.4GB drive), and IMHO are not particularly

relevant for most Linux users.

The Linux kernel uses as much RAM as possible to cache hard disk data

accesses, and so if data is not in the kernel cache there is little chance

that it will be in the (much smaller) hard disk cache.

2) Processor utilization

Unfortunately, it is very difficult to gather data about processor

utilization during data transfers, but this is exactly the biggest advantage

of DMA transfers over PIO transfers. My estimate is that CPU utilization

during UDMA transfers will be as low as 3-4%, while being somewhere around

30% for PIO transfers and 6-8% for DMA mode 2.

3) UDMA vs SCSI

The main advantage of DMA mode 2 and UDMA over SCSI is that the controller

is already on your motherboard, so why not use it?

Mark Lord's triton.c driver has a very small latency and so UDMA drives

may beat their Ultra-Wide SCSI-2 counterparts in some cases (at equal

spindle speeds) e.g. lots of small files (loaded news servers) being

read/written at irregular intervals.

Note however that SCSI drives are available at spindle speeds of 7,200,

10,000 and even a recently announced 12,030 rpm. IBM is planning some 7,200

rpm UDMA EIDE drives, but those are not yet available. Seagate has just

released its EIDE 7,200 rpm drives, but they have special cooling

requirements just like their SCSI counterparts. Expect this technology to

become commonplace by the end of 98, though.

The UDMA burst data transfer rates exceed maximum head transfer rates

(maximum head transfer rates in the industry have reached 160 Mbits/s in

1998) and so for large files neither Ultra-Wide SCSI-2 nor UDMA will have an

advantage over the other technology.

It used to be that high-capacity drives were only available with SCSI

interfaces, but this isn't true anymore. Right now top capacity for an EIDE

drive is Maxtor's 11.3Gb monster, which is quite affordable in fact. One can

drive four of these with a standard motherboard: 45Gb for < $2k.

SCSI drives can chain, overlap and re-order commands, EIDE drives cannot.

However, Linux already has an intelligent "elevator" algorithm for hard disk

accesses.

At present, EIDE top speed is 33MB/s burst. Ultra-Wide II SCSI is 80MB/s

burst. The cost of an Ultra-Wide II SCSI controller + 9Gb hard disk is > 4 x

the cost of an 8GB UDMA drive. IMHO the price/performance ratio of UDMA

beats SCSI.

A new standard is emerging called ATA-66, which will double the burst

transfer speed of EIDE drives to 66Mb/s. I don't have any technical info

about it, unfortunately. The first ATA-66 drives will be shipped by Quantum

in 1999, but VIA has already announced two ATA-66 capable chipsets (in fact

based on the same Southbridge chip); as I write this, data sheets are not

available to the general public. Probably Intel will come out with a chipset

of its own with ATA-66 capabilities.

4) What is the best UDMA chipset/hard disk?

Intel designed the first DMA mode 2 capable chipset, the FX (Triton I) a few

years ago. The Linux DMA mode 2 driver was initially written by Mark Lord

for the original Intel FX chipset and appeared around kernel 1.3.20 if I

remember well. The later HX and VX chipsets had exactly the same DMA mode 2

capabilities and the triton.c driver was for a long time Intel-only. Mark

planned to support the Opti Viper chipset but Opti went out of the

motherboard chipset business so fast that Mark didn't even have the time to

get his hands on an Opti motherboard, I guess.

Intel later introduced a UDMA compatible motherboard chipset with its TX

chipset. Kernel 2.0.31 was the first Linux kernel to support the TX chipset,

however only DMA mode 2 (16.6MB/s) was supported.

The TX chipset has a proven record of reliability. But DMA mode 2 and UDMA

transfers on the TX suffer from a flaw common to previous Intel DMA mode 2

only chipsets: a single data buffer is shared between the two IDE channels.

This buffer (64 bytes deep) is used to hold data on its way from the PCI bus

to/from the hard disk's small cache. A hardware arbitration mechanism

prevents data loss when the OS tries to simultaneously use both IDE

channels.

VIA chips also have a single FIFO, with the same 64 bytes deep buffer.

However, VIA chips can have the buffer split 1:1 or 3:1 between both IDE

channels; an interesting feature, but difficult to use.

How is this FIFO buffer used? Remember that the PCI bus can transfer data at

a maximum rate of 132MB/s when clocked at 33MHz, 150MB/s when clocked at

37.5MHz (maximum safe clock speed for PCI is 33MHz, after that well..). So the

PCI bus mastering IDE controller will be transfering data from main memory

DRAM to this FIFO buffer in small bursts of < 64 bytes, then from the buffer

to the IDE disk drive cache (when writing; the other way around for reads).

I recently managed to get hold of the SiS 5598 data sheet and studied the

IDE controller part of this highly integrated chip, a device identified by

the number 5513. The 5598 even includes an SVGA controller, which should be

disabled if one wants to get decent performance from this chipset: it

severely limits CPU/memory bandwidth. The SiS5597 is the same part with

a different pinout.

It appears the 5513 has two completely independent IDE channels, each with

its own 64 bytes deep data buffer. On disk-to-disk or CD-to-disk transfers,

the 5598 and 5591 chipsets will easily beat the Intel TX and VIA. On

simultaneous (U)DMA transfers to two disks (for example, when the Linux md

driver is used to create a RAID-0 array with data striping), the 5513 device

will be faster than the TX Southbridge device since there will be no

contention for the data buffer, assuming each drive is connected to a

different IDE channel.  Other PCI bus related features will also improve its

performance of the SiS devices. So, compared to the Intel TX and various VIA

chipsets, the 5598 and 5591 win hands down in terms of UDMA implementation.

Unfortunately, it is very difficult to get data sheets for the ALi Aladdin

IV+ and Aladdin V chipsets. These newer chipsets support up to 1 MB of L2

SRAM cache, the AGP bus (2X), 100 MHz CPU bus and of course, UDMA data

transfers. The newest VIA chipset for Socket 7 motherboards beats them all

in terms of features, as it sports ATA-66 compatibility.

On the UDMA hard drive front, the present performance leaders are the IBM

Deskstar drives. These drives have relatively large data caches (476kB

available), a 5,400 rpm rotational speed and < 10ms random access times.

They run very cool and although they can't be called silent, their noise

level is acceptable. They are also reliable.

Seagate has just begun shipping 7,200 rpm EIDE drives which will obviously

benefit from the lower data latency. They are reported as particularly

silent due to the use of Fluid Dynamic Bearing motors, but running quite

hot. IMHO if one has to add a fan to cool them, this defeats any advantage

these drives will have in terms of noise level. Another advantage of this

technology is the lower vibration levels compared to ball bearings.

IBM has pre-announced very large capacity (14GB), 7,200 rpm EIDE UDMA drives

a month ago, but those are not shipping yet. They are based on a new head

technology called Giant Magneto-Resistive Heads, which is supposed to

increase the data density on the disks by a factor of 4 or more. More details

when I get my hands on one. IBM licensed Western Digital to use this

technology.

Quantum has always shipped among the best and fastest EIDE drives, and they

worked with Intel to create the UDMA standard. They used to have the fastest

drives for Linux DMA mode 2 transfers (see the comments in

/Documentation/ide.txt).

Well, I just got an email from Denny de Jonge  that proves

Quantum drives will keep their reputation:

"Andre,

 After I applied the UDMA-patch for Linux 2.0.33 hdparm showed up with the

 following benchmarks:

 /dev/hda:

 Timing buffer-cache reads:   64 MB in  1.02 seconds =62.75 MB/sec

 Timing buffered disk reads:  32 MB in  3.02 seconds =10.60 MB/sec

 Not bad, don't you think ?

 These results have been obtained using the Intel 82371 Chipset and a

 Quantum Fireball 4.3SE harddisk."

I later asked what kind of processor Denny was using: it's a 266MHz PII.

BTW I have been collecting hard disk/file subsystem benchmarking information

based on bonnie, a popular benchmark available for Linux. I have come to the

conclusion that bonnie is not a reliable benchmark when it comes to

comparing different systems, basically because it depends so much on how

much RAM one has installed and how much of it is free, as well as system

load, CPU speed, etc. For this reason I will not quote bonnie results

anymore. For comparative benchmarking between two hard disk drives on

exactly the same hardware it may be acceptable, but otherwise it's too

unreliable as an indicator of performance.

Unreliable drive + motherboard + driver combination

---------------------------------------------------

Quoting Kim-Hoe Pang:

"The UDMA mode of an UDMA drive would NOT be enabled on a non-UDMA capable

chipset mobo. On power-up or after a hardware reset, the drive is in normal

PIO/DMA mode. To enable the UDMA mode in the drive, the host, BIOS or OS,

needs to send a SET FEATURE ("enable UDMA mode subcommand") AT command to

the drive. A non-UDMA capable mobo will not send this command to the drive.

UDMA mode is dis/enabled via BIOS setup. The patch does not attempt to

override user's BIOS setting."

There may be some combinations of drives, motherboards (BIOS) and Linux

driver which may prove unreliable. Remember we are transfering data at

33MB/s over unshielded ribbon cable in a very noisy (electromagnetically

speaking) environment.

In the future it would be nice if hard disk manufacturers would publish the

timings required by their drives, and chipset manufacturers would follow a

single standard for registers and controller architecture. Right now UDMA is

extremely timing sensitive.

A few recommendations for troubleshooting:

1) Make sure you have the latest BIOS for your motherboard. Connect to the

motherboard manufacturer's Web site and download the latest BIOS image file

and EEPROM flashing utilities. Check your BIOS version, and only flash your

EEPROM if needed.

2) Keep the IDE cable going from the motherboard to the drive short, and do

not loop it around another cable. I recommend < 30 cm (12") total cable

length.

3) If you have just a single UDMA hard disk drive per channel (which I

recommend), use the connectors at both ends of the cable to connect

motherboard and drive, do _not_ use the middle connector. If you have a UDMA

hard disk drive and a CD-ROM drive on the same cable, plug the hard disk

drive at the end of the cable (use the middle connector for the CD-ROM

drive). Also the hard disk must be the master EIDE device, the CD-ROM drive

the slave EIDE device, never the other way around (this is not determined by

cable position, but by small jumpers on the drive and at the back of the

CD-ROM). The same rules apply to CD-RW, ZIP and tape EIDE drives.

4) If you have (shudder) Windows 95 installed in your system, and have been

able to use UDMA, you should be able to use UDMA with Linux.

5) DON'T OVERCLOCK the PCI bus. 33MHz is the maximum supported speed for

the PCI bus. Some (supposedly compatible) UDMA drives will not even take

37.5MHz, but should be OK at 33.3MHz.

In any case, NEVER, NEVER set the PCI bus to 41.5MHz.

The RECOMMENDED safe setting is 33MHz.

Adequate testing is needed in each case. The golden rule here, as always:

backup, backup, backup.

Aknowledgments

--------------

Mark Lord for his excellent, reliable and very readable triton.c driver code

and all his (E)IDE Linux programming.

Kim-Hoe Pang for the first UDMA patch against kernel 2.1.55.

Christian Brunner for his patch converting triton.c into a generic DMA mode

2 EIDE driver.

Brion Vibber for his neat Linux UDMA mini-HOWTO, for his help and

contributions to this package, and for bearing with my various documentation

changes and suggestions.

Michel Aubry for his complete VIA support and neat diagnostics code, as well

as the patch to hdparm to support UDMA.

Andre Hedrick for his great code for the various PCI UDMA controller cards.