[Oberon] FPGA - Save / Restore OBERON.FS

[Skulski, Wojciech]

Chris:

  thank you for the thoughtful description. It closely mirrors the way we used a data acquisition about twenty or thirty years ago. It was the Age of the Magnetic Tape. I still remember these large 1/2" magnetic tape rolls and how they would spin. These were replaced by the Exabyte cartridges. Much smaller, but in essence the same. The access was sequential. The file would get open, written to, then closed. (We called these files "runs" and we referred to them by sequential numbers.) Once the run was closed, it could not be reopened. A new run would be opened, written to, and then closed. At some point the magnetic tape was almost full. It was then removed from the magnetic tape station and replaced with a fresh tape.

At some point in history, the disks grew up in the capacity enough to replace the tapes. The disks are random access, so now we could list the directories, selectively copy the files, etc. The file names on disks did not necessarily have the form "run000xx.dat" anymore. However, in most experiments the "data acquisition disks" are still being used much the same way as the old style tapes. The big difference is that the DAQ disks (usually RAID arrays these days) are not moved by hand to the data analysis computers. They are rather emptied over network. The DAQ disks thus serve as large FIFOs for the data runs.

I would say yes, this kind of data recording was sufficient back then. The same philosophy is now applied to the DAQ disks, even though these are random access.

I think that your description accurately captured the thought behind the data logging applications.

Thak you,
Wojtek
________________________________________
From: Oberon [oberon-bounces at lists.inf.ethz.ch] on behalf of Chris Burrows [chris at cfbsoftware.com]
Sent: Friday, April 21, 2017 10:27 AM
To: 'ETH Oberon and related systems'
Subject: Re: [Oberon] FPGA - Save / Restore OBERON.FS

> > From: Skulski, Wojciech skulski at pas.rochester.edu
> > Sent: Thu Apr 20 06:42:54 CEST 2017
>
> > My biggest concern about Oeron FS is its limited size.
>

What do you plan to do with the Oberon filesystem that makes the size a
problem? The solution might not necessarily be to increase its size. For
example:

My primary Project Oberon-related task is to support its use in embedded
software applications. The size of the file system could be an issue when
performing high-speed data logging. However, the Project Oberon, FAT and
other general-purpose filesystems were not designed for this sort of
realtime operation. Simply making the filesystem larger is likely to make it
even less suitable.

Fortunately, an additional special-purpose filesystem can be readily
implemented for this task if we limit the requirements to what is necessary
and sufficient.

To avoid data loss during realtime operation we need efficient code and fast
and predictable disk access speeds. SDHC cards (as with most other file
storage systems) are significantly more efficient when accesses are
sequential rather than random. Hence, the proposed requirements are:

1. On the embedded system the filesystem is write-only.
2. Disk writes are purely sequential.
3. Unlimited free space beyond the first 320MB of an SDHC can be used.
4. Larger file sizes is a higher priority than the number of files.
5. Multiple files can be created but all the space could be used by a single
file if required.
6. Only one file can be open for writing at any one time.
7. Once a file is closed it cannot be written to again.

Software would be written to transfer the files directly from the SDHC card
inserted into a PC for processing and analysis. The PC would also be used
for file deletion and other disk maintenance operations.

If anybody has a use for such a facility I would like to know if, and why,
any of the above requirements would be too restrictive for your use,

Regards,
Chris Burrows
CFB Software
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