CF Performance settings

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Hi all,

Is anybody knows how to configure CompactFlash for best performance.
What register ? May be FEATURE_REG in ATA's ?

My design reaches about 150Ko/s which is far from CF spec.

Thank you all, Habib.

Re: CF Performance settings
On Fri, 18 Feb 2005 19:42:22 +0100, habib bouaziz-viallet

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Throughput is defined by many factors. Are you acessing it with 16
bit's or 8, is DMA used or not? The low level IO routines (transfering
sector data) is written in assembly ? Just by writing the low level
routines in assembly I once could increase the throughput by the
factor of 5.. Ok, this very much dends on the quailty of the compiler
in use but there it made a huge difference.

Memory mapped mode (wich btw. is quite a misleading term in the
context of CF) can have an advantage if the host CPU you are using is
supporting IO instructions or other kinds of fast external memory
transfers. In this mode, the CF simply ignores the address lines
during data transfer hence block move operations that the CPU may
supports can be used where as otherwise you must feed every single
byte (or word in 16 bit mode) through the date register. If your CPU
does not support memory block move operations there is not much
advantage (performance wise) in useing memory mapped mode over true
IDE or IO mode.



Re: CF Performance settings
Le Fri, 18 Feb 2005 22:59:57 +0100, Markus Zingg a écrit :

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Hi Markus,

Hardware : Atmega64 driving CF ATA_media with no DMA, no IT, so CF is
driven in memory mapped mode. All transferts CF <--> AVR are 8 bits width.

In order to increase Read/Write perfs, trying to deal with asm provided by
gcc is on the go. But i read that CF ATAmedia enters Sleep mode after a
programmable delay if no activity.
How to configure that delays (Sleep to Write, Sleep to Read) after
carrefully reading Sandisk and ATA_CF specs no further infos is clearly
Have you ever dealing with ?

Many thanks, Habib

Re: CF Performance settings
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I don't know the ATmegas good enough to know if they support memory
block move operation on asm level. If so, then this is the way to go
since it will be the best you can do to transfer sector data.

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IMHO the sleep mode is completely transparent and out of my experience
can't really be the reason for the low transferrate you experience.
I'm of course asuming you are not waiting seconds between individual
sector transfers :-) Just implement the low level code in assembly
(again, using the a10 pin high feature i.e. blocktransfer) and I'm
very sure you will achive the maximum trhoughput possible with your
controller. The CF by itself (unless it's a really old one) should be
much faster than what your ATmega can move around.

I haven't used this feature, but so far I found the CF specs to be
well written. You may have to read it a couple of times though.


Re: CF Performance settings
Le Sat, 19 Feb 2005 14:26:04 +0100, Markus Zingg a écrit :

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After re-implement Read and Write sectors functions (mostly in asm),
speed-rate is now about 230 Ko/s with ATmega running at 7,37MHz. Yet
another proof that hand-coding assembly is sometimes far better than
anyother compiler, even gcc.
PS : Sleep to read/write delays may be configured through IDLE command
(Cf. CF datasheet)

Thank you, Habib

Re: CF Performance settings
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Hi. It's all about how fast you can transfer blocks of bytes between your
CPU and the CF device. There are ATA commands that enable write buffering
and multi-sector transfer modes, but I wouldn't worry about those for now.
Just concentrate on writing a highly optimised function for transfering a
block of 512 bytes (one sector) between the CPU and the CF device; this is
where most of the performance gain will come from. Move as much data from
memory into the CPU registers as you can, then transfer those as fast as you
can and repeat this in as tight a loop as possible. Of course, you shouldn't
transfer faster than the card can handle; there is a field in the CIS (Card
Information Structure) that reports the supported speed. However, you're
unlikely to get close to the imit of the card with your CPU.


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