[Oberon] RISC.img format

[eas lab]

Nice thread.
I'm interested in disks & MBR and don't see how other can avoid it.

Jorg wrote:
>If you want to use the rest of your SD card, add a third partition in the
>MBR after the Oberon partition.

Tomas wrote:-
]what would be the size of a 3rd partition,

Do you put it in a <linux driven> card reader & see the partition sizes,
including the tail/rest/unformatted ?

== Chris Glur.


On 3/20/16, Tomas Kral <thomas.kral at email.cz> wrote:
> Hi Joerg,
>
> Aha, that corresponds to Ceres workstation, I read somewhere 40MB SCSI,
> and 10MHz processor clock. FPGA project clearly outperforms the 80'ies
> hardware.
>
> Yes I am interested in your code, what would be the size of a 3rd
> partition, I can imagine it is a clone o the primary OBS 64MB one?
>
> Many thanks.
>
> --
> Tomas Kral <thomas.kral at email.cz>
>
> On Sun, 2016-03-20 at 09:20 +0100, Jörg Straube wrote:
>> Hi Tom
>>
>> the RISC.img is an "normal" ISO file with an MBR. The MBR is populated
>> with two partitions.
>>
>> The first one  (256 MB) is just there and is not used by Oberon at all. It
>> can be (re)formatted to any filesystem you like.
>>
>> The second partition (64 MB) is the Oberon filesystem. It has to be at
>> that location (256 MB from the start of the disk) as the Oberon bootloader
>> does NOT read the MBR to find the first Oberon sector. It just reads
>> directly from a fixed position and reads in some 1K sectors to load the
>> system.
>>
>> The Oberon filesystem is currently limited to 64 MB as  Kernel.Mod keeps a
>> fixed sector map (VAR sectorMap) of 64k bit (CONST mapsize) Each bit
>> represents a sectior of 1K  --> 64k * 1kB = 64 MB.
>>
>> 64MB is the maximum size an Oberon system can hold. The actual size of the
>> few files distributed in RISC.img is much smaller; below 500kB.
>>
>> If you want to use the rest of your SD card, add a third partition in the
>> MBR after the Oberon partition.
>>
>> I wrote Oberon code to copy files from and to the second partition of
>> RISC.img. If your interested, I can send you my code.
>>
>> Jörg
>>
>> > Am 19.03.2016 um 16:09 schrieb Tomas Kral <thomas.kral at email.cz>:
>> >
>> > Dear Paul,
>> >
>> > I bought Pepino LX9 board recently. I am studying Project  Oberon 2013,
>> > making my firsts steps. My earlier experience comes from Pascal and
>> > Modula on ATARI-ST.
>> >
>> > I asked a similar question about RISC.img format here,
>> > http://saanlima.com/forum/viewtopic.php?f=14&t=1280&sid=6771605d7bfdce198fa7d7cba611aab7
>> >
>> > fdisk reports vfat and OBS partitons on my uSD card imaged with
>> > RISC.img, size 256MB.
>> >
>> > Having read chapters on file system - Files.Mod, FileDir.Mod,
>> > I wish to know, if OBS partition grows somehow, so I can get more
>> > sectors allocated on my 2GB uSD?
>> >
>> > I also missed the point of media formating, as FileDir.Mod does not seem
>> > to provide Format command in its ToolBox.
>> >
>> > Many thanks.
>> >
>> > --
>> > Tomas Kral <thomas.kral at email.cz>
>> >
>> >
>> >>
>> >>
>> >> Dear Oberoners,
>> >>
>> >> I've been asked a couple of questions about the RISC.img SD-Card image
>> >> downloadable from http://projectoberon.com for the FPGA RISC5 Oberon
>> >> systems.  (If you can, please post questions publically rather than
>> >> emailing me privately - otherwise I have to assume it's a private
>> >> matter
>> >> which is more time-consuming to deal with - if I can ever get to it -
>> >> and
>> >> doesn't benefit others.)
>> >>
>> >> The RISC Oberon system boots from an SD-Card and uses it as its file
>> >> system.  This filesystem is much simpler than common contemporary
>> >> filesystems such as FAT, FAT32, NTFS, exFAT, EXT4 etc. and is not in
>> >> any
>> >> way compatible.  (On the original Ceres, the backup floppy disk format
>> >> was
>> >> very close to the FAT12 format, but with an altered directory to cope
>> >> with
>> >> long filenames, which were not in those days supported on FAT).
>> >>
>> >> It would have been easy to make the RISC5 Oberon filesystem (including
>> >> its
>> >> reserved area for the bootfile) begin at offset 0 from the beginning of
>> >> the SD-Card.  This would have dedicated the SD-Card to Oberon use, but
>> >> simplified the bootloader.
>> >>
>> >> Or alternatively, the Oberon filesystem could have perhaps been stored
>> >> as
>> >> a file in the FAT filesystem on the SD-Card, making it much more
>> >> accessible to utilities running on other computers.  But this
>> >> convenience
>> >> would have come at a high cost: it would have made the bootloader much
>> >> more complicated, and given many more possibilities for distracting
>> >> problems in development.
>> >>
>> >> In the end, it was decided to place the Oberon filesystem at a fixed
>> >> offset from the beginning of the disk.  This was a trivial change to
>> >> the
>> >> bootloader, keeping it easily-understandable and within one block ram
>> >> (BRAM) of the FPGA.
>> >>
>> >> This meant that FAT-compatible data structures, and a reasonable-size
>> >> and
>> >> perhaps useful (256MB) FAT partition could still exist at the beginning
>> >> of
>> >> the disk.  If this FAT partition has nothing in it, it compresses very
>> >> well and therefore does not significantly increase the RISC.img
>> >> download
>> >> time.
>> >>
>> >> The MBR partition id for the Oberon filesystem was chosen as 0FFh,
>> >> because
>> >> the ids are historically rather a free-for-all and the filesystem is
>> >> not
>> >> exactly the same format as any that have gone before, even the ETH
>> >> PC-based Oberon filesystems.  0FFh is clearly an arbitrary value, and
>> >> also
>> >> was only used by others for private data structures rather than for
>> >> filesystems which were interoperable amongst systems.
>> >>
>> >> Note that a lot of the motivation for this was defensive.  For example
>> >> it
>> >> makes it more difficult for the Oberon filesystem to be destroyed when
>> >> the
>> >> SD-Card is inserted in a Windows system.
>> >>
>> >> When submitting some early additions to Peter de Wachter's RISC
>> >> emulator
>> >>
>> >> https://github.com/pdewacht/oberon-risc-emu
>> >>
>> >> for emulated RS232 file transfer which he kindly incorporated, I also
>> >> included a quick check on startup which allows the use of a disk image
>> >> which only contains the Oberon file system (called .OBERON.FS in the
>> >> Windows binary distribution of the emulator which I put on
>> >> http://projectoberon.com).
>> >>
>> >> This check is for the magic number 9B1EA38DH (FileDir.DirMark) which is
>> >> at
>> >> the beginning of the root directory sector.  Oberon uses a "parity"
>> >> scheme
>> >> for sector numbers, making all of them divisible by 29, so the first
>> >> usable Oberon sector, number 29, begins at SD-Card sector offset
>> >> 80002H.
>> >> This slightly odd value comes from the fact that SD-Cards have 512-byte
>> >> sectors, but Oberon uses two of these (1K) for each Oberon sector, and
>> >> that sector 0 is not used.
>> >>
>> >> So if you are using a nice operating system and you know what you are
>> >> doing (because it allows dangerous commands such as dd) you can extract
>> >> the Oberon file system from the image with a command like (262145 =
>> >> 40001H
>> >> = 80002H * 512 DIV 1024)
>> >>
>> >>  dd if=RISC.img of=.OBERON.FS  obs=1024 ibs=1024 skip=262145
>> >>
>> >> and you can even (sudo) write it directly back to a real SD-Card with
>> >> something like
>> >>
>> >>  dd if=.OBERON.FS of=/dev/disk1 obs=1024 ibs=1024 seek=262145
>> >>
>> >> The name .OBERON.FS was chosen to make it look like a system file,
>> >> which
>> >> would be totally destroyed if someone opened it and saved it with a
>> >> text
>> >> editor, for example.
>> >>
>> >> Hope that's useful!
>> >> Cheers,
>> >> Paul
>> >>
>> >>
>> >> --
>> >> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related
>> >> systems
>> >> https://lists.inf.ethz.ch/mailman/listinfo/oberon
>> > --
>> > Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
>> > https://lists.inf.ethz.ch/mailman/listinfo/oberon
>> --
>> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
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> --
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>