Re: Sandisk Compact Flash

David Hinds
2005-07-15T05:23:16Z

On Wed, Jul 13, 2005 at 07:04:38PM +0530, somshekar.c.kadam@in.abb.com wrote:
>
> I ma newbie to compactflash driver , I am using mpc862 PPC processor
> on my custom board having 64mb ram running linuxppc-2.4.18 kernel .
> i am using Sandisk Extreme CF 1GB which is 133x high speed, but
> found the performance with other kingston 1GB CF with slower speed ,
> is both same , CF is implemented on pcmcia port , i am not sure what
> is the mode set for transfer , Feature set command is used in which
> it sets the PIO mode or Multiword DMA transfer mode by specifying
> its value in Sector count register , i am not able to understand in
> linux kernel ide driver where this is set , is it by default set ,
> this mode is set or we need to set it , i think we should assign
> this value , right now i am not able to trace this in my code. ,

All Compact Flash cards, in 16-bit PCMCIA card readers, operate in PIO
mode 1 (polled IO, no DMA), which means you will get only about 1
MB/sec regardless of the card's claimed tranfer speed. Some cameras
also only support this mode; others will run CF cars in "TrueIDE"
mode, which is required to use the DMA transfer modes.

There are high performance CF card readers that can use TrueIDE mode:
both CardBus ones and Firewire ones. For example:

http://www.dpreview.com/news/0310/03102103delkincardbustest.asp

It sounds like your card reader is one of the slow 16-bit ones.

-- Dave