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Date: Fri, 23 Jan 2009 11:30:53 +0100
From: Bernd Walter <ticso@cicely7.cicely.de>
To: Alexander Motin <mav@FreeBSD.org>
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Cc: freebsd-arm@FreeBSD.org, ticso@cicely7.cicely.de, ticso@cicely.de
Subject: Re: Mount root from SD card?
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On Fri, Jan 23, 2009 at 11:17:06AM +0200, Alexander Motin wrote:
> > Right now I'm only getting ~900kB/s (890-919) and we can do much
> > better, no?
> 
> I have started from alike values with sdmmc driver, but with multiblock transfers and 4 bits bus I have reached top possible for my controller 15Mbytes/s. Multiblock transfers are very important to reduce number of interrupts.

Not only that - they are important for card internal optimization.
Especially with writing a transfer can issue read-modify-write cycles
on the large cell blocks and writing a 16k FS block in 32 card
transactions is not very perfect.
Especially many MLC cards have a large write transaction overhead.
With reading it just means opening the cells for reading, but some
card designs are slow with this as well.

-- 
B.Walter <bernd@bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.