Re: FreeBSD as read-only firmware

On Sat, Nov 3, 2012 at 8:30 AM, Ian Lepore <freebsd_at_damnhippie.dyndns.org>wrote:

> On Sat, 2012-11-03 at 08:01 -0700, Mehmet Erol Sanliturk wrote:
> > I do not know exact data transmission rate of SDHC cards , but , I
> > think ,
> > it is faster than CD or DVD . For CD and DVD , at present there is NO
> > any
> > only READ CD or DVD devices . They are disappeared from the market .
> > For
> > writable CD or DVD , it may be possible to append some files at the
> > end of
> > recorded area , and the media may be corrupted by re-recording ( I
> > think ) .
>
> Expect roughly 22-25MB/sec on a modern SDHC with a 4-bit datapath.
>
> Be aware that there's no way to truly write protect an SD card.  There
> is a write protect tab on a full-size card (but not on a MicroSD), but
> it's not enforced in the card's hardware, it is a polite request to the
> system "please don't write to this card" and some systems don't even
> have the hardware to sense the switch position.
>


Another option may be to use READ-ONLY USB card readers , if they really
are only readable ( which do not contain write circuitry ) . I am reading
information about such devices in company web sites which write is not
possible , and write able USB card readers are sold with that feature
specified .
I do not know exactly how they are working .



>
> Since it's flash-memory based, it also may corrupt the media on write,
> including the possibility of corrupting existing data that has no
> relation to the new data being written.  That is, you could have a
> write-protected partition and a write-enabled partition on the same
> SDCard, and writing into the write-enabled partition can damage data on
> the write-protected partition.  This is because you have no control over
> the way the embedded flash microcontroller allocates storage internally,
> and it is free to place data pages from unrelated filesystems into the
> same blocks (block = erase/programming sized unit).
>
> I suspect all off-the-shelf nand-flash based storage has the same
> problems, but CF and SDCard are the only ones I've got hands-on
> experience with.  At work we're now moving away from CF and SDCard and
> towards putting nand flash chips directly onto our boards, and using
> FreeBSD to access them rather than relying on the behaviors of some
> embedded microcontroller we know nothing about.
>
> -- Ian
>
>
>

Thank you very much .

Mehmet Erol Sanliturk