Date: Sat, 3 Nov 2012 09:03:18 -0700 From: Mehmet Erol Sanliturk <m.e.sanliturk@gmail.com> To: Ian Lepore <freebsd@damnhippie.dyndns.org> Cc: Alexander Yerenkow <yerenkow@gmail.com>, lev@freebsd.org, freebsd-current <freebsd-current@freebsd.org> Subject: Re: FreeBSD as read-only firmware Message-ID: <CAOgwaMsa_HZWC0ztgmVcT=MbWHh9AnNYjxWfjfbWW106vWjh%2Bg@mail.gmail.com> In-Reply-To: <1351956625.1120.44.camel@revolution.hippie.lan> References: <CAPJF9wmO-oO7cy4XUwnTMb5cpD14TaK430rWW2nqodBFWw54DQ@mail.gmail.com> <1167404891.20121103170049@serebryakov.spb.ru> <CAPJF9wmVPxMDBqyy=Dqdnb%2BZ33f_wLDx9CFbk_oSEx4inboK6A@mail.gmail.com> <CAOgwaMtnqCvA3_zyd1fqmEFyrTD4hZHoE5QZC0akmK0DTm8=yw@mail.gmail.com> <1351956625.1120.44.camel@revolution.hippie.lan>
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On Sat, Nov 3, 2012 at 8:30 AM, Ian Lepore <freebsd@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
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