From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailout02.sul.t-online.com ([194.25.134.17]) by canuck.infradead.org with esmtp (Exim 4.33 #1 (Red Hat Linux)) id 1BaiLI-0001Sw-KR for linux-mtd@lists.infradead.org; Wed, 16 Jun 2004 17:53:15 -0400 From: "Thomas Gleixner" To: "Dan Brown" , "Slim" , Date: Wed, 16 Jun 2004 23:47:20 +0200 References: <20040616161345.33330.qmail@web50802.mail.yahoo.com> <083701c453df$c65db960$0100a8c0@superfortress> In-Reply-To: <083701c453df$c65db960$0100a8c0@superfortress> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Message-Id: <200406162347.20436.tglx@linutronix.de> Cc: Subject: Re: [PATCH] Towards DiskOnChip support as a NAND driver Reply-To: tglx@linutronix.de List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wednesday 16 June 2004 22:23, Dan Brown wrote: > > ECC - hardware error correction by the device? Is this an optional > > enable in the driver? > > Yes, the DOC has an ASIC that does ECC computation (for actual error > correction, software assitance is required). It's not optional, though it > could be made so.... Why would you want to turn it off? It has two advantages over software ECC. 1. The software ECC is a Hamming code which can correct 1 bit errors and=20 detect 2 bit errors. The HW ECC on DOC devices is a Reed Solomon Encoder /= =20 Decoder which allows to correct and detect more errors 2. In general a HW based ECC generator is a lot faster than the software=20 version as it gets you rid of a ugly loop through all the data bytes on eac= h=20 read / write. A small drawback is the error correction for reed solomon, as it is more =20 complex and slower than for hamming codes. This is not too bad as error=20 correction usually starts to happen when the device wears out, but then the= =20 hamming code which we use in soft ecc can be rather unsufficient.=20 The speed improvement on write and read is really worth to use hw ecc if it= s=20 thers =2D-=20 Thomas _____________________________________________________________________ =46rom slash dot org "When customers are visiting, engineers are not allowed to wear ties.=20 That way the customer can tell who is the engineer and who is the=20 salesman (and therefore whom to believe.). Ties cut off blood flow=20 to the brain, making it easier for the salesmen to do their jobs."=20 _____________________________________________________________________ linutronix - competence in embedded & realtime linux http://www.linutronix.de mail: tglx@linutronix.de