linux/drivers/char/ftape

Some notes for ftape users with PCI motherboards:
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The problem:
------------

There have been some problem reports from people using PCI-bus based
systems getting overrun errors.
I wasn't able to reproduce these until I ran ftape on a Intel Plato
(Premiere PCI II) motherboard with bios version 1.00.08AX1.
It turned out that if GAT (Guaranteed Access Timing) is enabled (?)
ftape gets a lot of overrun errors.
The problem disappears when disabling GAT in the bios.
Note that Intel removed this setting (permanently disabled) from the
1.00.10AX1 bios !

It looks like that if GAT is enabled there are often large periods
(greater than 120 us !??) on the ISA bus that the DMA controller cannot
service the floppy disk controller.
I cannot imagine this being acceptable in a decent PCI implementation.
Maybe this is a `feature' of the chipset. I can only speculate why
Intel choose to remove the option from the latest Bios...

The lesson of this all is that there may be other motherboard
implementations having the same of similar problems.
If you experience a lot of overrun errors during a backup to tape,
see if there is some setting in the Bios that may influence the
bus timing.

I judge this a hardware problem and not a limitation of ftape ;-)
My DOS backup software seems to be suffering from the same problems
and even refuses to run at 1 Mbps !
Ftape will reduce the data-rate from 1 Mbps to 500 Kbps if the number
of overrun errors on a track exceeds a threshold.


Possible solutions:
-------------------

Some of the problems were solved by upgrading the (flash) bios.
Other suggest that it has to do with the FDC being on the PCI
bus, but that is not the case with the Intel Premiere II boards.
[If upgrading the bios doesn't solve the problem you could try
a floppy disk controller on the isa-bus].

Here is a list of systems and recommended BIOS settings:


        Intel Premiere PCI (Revenge):

Bios version 1.00.09.AF2 is reported to work.



        Intel Premiere PCI II (Plato):

Bios version 1.00.10.AX1 and version 11 beta are ok.
If using version 1.00.08.AX1, GAT must be disabled !



        ASUS PCI/I-SP3G:

Preferred settings:     ISA-GAT-mode : disabled
                        DMA-linebuffer-mode : standard
                        ISA-masterbuffer-mode : standard


        DELL Dimension XPS P90

Bios version A2 is reported to be broken, while bios version A5 works.
You can get a flash bios upgrade from http://www.dell.com


To see if you're having the GAT problem, try making a backup
under DOS. If it's very slow and often repositions you're
probably having this problem.

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 LocalWords:  ftape PCI bios GAT ISA DMA chipset Mbps Kbps FDC isa AF ok ASUS
 LocalWords:  SP linebuffer masterbuffer XPS http www com