From owner-freebsd-current@FreeBSD.ORG Sat Nov 3 16:03:20 2012 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 034B6D16; Sat, 3 Nov 2012 16:03:20 +0000 (UTC) (envelope-from m.e.sanliturk@gmail.com) Received: from mail-vc0-f182.google.com (mail-vc0-f182.google.com [209.85.220.182]) by mx1.freebsd.org (Postfix) with ESMTP id 7C2648FC0A; Sat, 3 Nov 2012 16:03:19 +0000 (UTC) Received: by mail-vc0-f182.google.com with SMTP id fw7so6162672vcb.13 for ; Sat, 03 Nov 2012 09:03:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=wOFSHQ3WSAWpoppWjw9ooJxFcbPZO3yUxAFEbNDsu+w=; b=A/h7W8MQRZG9vm5MhFLZJhrpgTcH/KRB5eG6hy6z7J5SNxoB8eoT/Li6+J28KBiluY cV64CNYydZBD8kGmsODvkiC9y+Qswa9l16JXMpb3nrD4gmAy0fSnccxg7k/LLgmQA8qM 8G4Qe4J52ixh/3zui2POrG23Wg33Tyqq3D7B+yD443oMNlqVGJZoqVfl7PIR9RLg+1lZ I5ztLewQkjU+a7g29UUBgukcGRb5IwFR9Sue3wbbHi0a0f92QRGCg7vmm6GEeQXsiX1W fxuqjHJuz+AxLDRooU1qyRaaKtDs3hmrT0yNNob9OmhEJCE3WBsx+fTxpNWQFFshJ0Zh jYgQ== MIME-Version: 1.0 Received: by 10.58.64.196 with SMTP id q4mr5064500ves.3.1351958598695; Sat, 03 Nov 2012 09:03:18 -0700 (PDT) Received: by 10.58.218.35 with HTTP; Sat, 3 Nov 2012 09:03:18 -0700 (PDT) In-Reply-To: <1351956625.1120.44.camel@revolution.hippie.lan> References: <1167404891.20121103170049@serebryakov.spb.ru> <1351956625.1120.44.camel@revolution.hippie.lan> Date: Sat, 3 Nov 2012 09:03:18 -0700 Message-ID: Subject: Re: FreeBSD as read-only firmware From: Mehmet Erol Sanliturk To: Ian Lepore Content-Type: text/plain; charset=UTF-8 X-Content-Filtered-By: Mailman/MimeDel 2.1.14 Cc: Alexander Yerenkow , lev@freebsd.org, freebsd-current X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 03 Nov 2012 16:03:20 -0000 On Sat, Nov 3, 2012 at 8:30 AM, Ian Lepore 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