linux-kernel - Re: [PATCH] mmc_spi: do propper retry managment in the block layer

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Date:	Tue, 19 May 2009 11:16:27 +0200
From:	Wolfgang Mües <wolfgang.mues@...rswald.de>
To:	"Matt Fleming" <matt@...sole-pimps.org>
Cc:	"Pierre Ossman" <drzeus@...eus.cx>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"David Brownell" <dbrownell@...rs.sourceforge.net>,
	"Mike Frysinger" <vapier.adi@...il.com>,
	linux-kernel@...r.kernel.org,
	"Nicolas Ferre" <nicolas.ferre@...el.com>
Subject: Re: [PATCH] mmc_spi: do propper retry managment in the block layer - rewritten

Matt,

Am Dienstag, 19. Mai 2009 schrieb Matt Fleming:
> Oh, wow. I didn't pick up on the fact that you were artificially
> generating errors on the bus.

I have started with observing random errors in a batch of 20 pre-production 
devices. There were about 1 error in 10 seconds of transfer due to an non-
optimal GND area design. Remember that for 25 MHz SPI clock, you only have
20ns from the start of the clock pulse into the SD card, and out of the
data line of the SD card and into the controller. This is fast - and induced 
EMP pulses of say 5 ns will be able to produce random transmission errors. 
And you can not apply any filtering to the data lines at 25 MHz - so you need 
some sort of fault tolerance in the software.

After that observation, I started to test these devices with an ESD pulse 
tester to test the software retry logic.

best regards

i. A. Wolfgang Mües
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