Hi,

I made some changes to the ATA driver runs on SanDisk
compact flash. SanDisk claim that it can read/write
multiple sectors with single sector read/write
command. In other words, the driver still issue single
sector read/write command, but I set 'n' sectors in
sector count register. I try it and it has been
working wonderfully for 2 years now.

Thanks!

Ferry

--- Artem Belevich <art@riverstonenet.com> wrote:
> Some time back I've whined about painfully slow I/O
> on CompactFlash
> cards in IDE mode. Looks like it could be improved.
> 
> To recap, under NetBSD/FreeBSD compactflash
> operations are several
> times slower than they are under Windows or Linux.
> 
> Recently I've spent some time tracking the problem
> and it looks like
> with some driver changes it would be possible to
> speed it up.
> 
> The issue is that:
> a) most CompactFlash cards claim to be capable of
> 1-sector PIO0
>    transfers only. I think it was a requirement in
> the CF+ spec before
>    rev1.4.
> b) CF cards have fairly long command-to-DRQ delay.
> One of Sandisk CF datasheets
>    says that it can be up to ~1.2ms. My measurements
> show the number pretty close 
>    to that.
> c) NetBSD driver issues a read command for *every*
> sector.
> 
> Here's a timeline for reading a single sector during
> 'dd bs=8192 count=<a lot>'.
> 
> 	     0   issue read command with sector count=1
> 	+~1300us interrupt happens  (first command takes
> long)
> 	+~ 250us fetch the data from the disk
> 
>         while(have sectors to read){
> 	    0	issue read command with sector count=1
> 	+~300us interrupt happens
> 	+~250us fetch the data from the disk
> 
> 	+  20us issue next command
> 	}
> 
> All in all it's ~570us/sector or <1Mb/s.
> 
> I've experimented a bit with ATA drivers I've got
> from
> http://www.ata-atapi.com/drvr.htm and with the same
> CF card I'm able
> to achieve ~3.3Mb/s read rate compared to ~900K/s
> I've got from the
> same card with NetBSD.
> 
> The main difference between ata-atapi.com's code and
> NetBSD is that
> NetBSD issues read command with 1-sector count and
> ata-atapi.com's
> driver reads several sectors at a time (32 in my
> case). 
> 
> The timings in this case looks like this:
> 
> 	     0   issue read command with sector count=N
> 	+~1300us interrupt happens  (first command takes
> long)
> 	+~ 250us fetch the data from the disk
> 
> 	while (more sectors) {
> 	         wait for next interrupt
> 	+   11us interrupt happens  (*** only 11us until CF
> delivers next sector.
> 	+  250us fetch data
> 	}
> 
> In this case it's ~260us/sector or ~2Mb/s.
> 
> So, if we could change NetBSD driver to issue single
> read command for
> N secors at a time, we'd be able to speed-up CF I/O
> quite a bit.  
> 
> Note that I'm talking about regular read/write
> commans (0x20/0x30),
> not read-multiple/write-multiple commands
> (0xc4/0xc5). I
> 
> Now, I'm not an expert on ATA/IDE and I'd appreciate
> if someone more
> familiar with the subject could take a look at the
> issue at see if and
> how it can be dealt with.
> 
> I wonder if the issue merits opening a PR for it.
> 
> --Artem
> 
> On Sun, Jul 14, 2002 at 07:26:00AM +0200, Wojciech
> Puchar <wojtek@chylonia.3miasto.net> wrote:
> > > Not the one(s) I have.
> > >
> > > wd1 at wdc0 channel 0 drive 0: <Hitachi
> CVM1.3.3>
> > > wd1: drive supports 1-sector PIO transfers, LBA
> addressing
> > > wd1: 244 MB, 695 cyl, 15 head, 48 sec, 512
> bytes/sect x 500400 sectors
> > >
> > > So far all the CompactFlash cards I saw
> (sandisk/lexar/io data/several
> > > no-names) reported themselves as PIO 0 with
> 1-sector-at-atime transfer
> > > capability. :-( I believe, that's what one of
> the earlier CF specs
> > > insisted upon.
> > >
> > > I saw some references to the multisector-capable
> CF cards on the web,
> > > but I haven't seen any of them myself yet.
> > 
> > i think it's possible they really can multisector
> but don't report. and
> > with >1sec/s will be same 3000us delay
> > 
> > 
> > >
> > > --Artem
> > >
> > > On Sat, Jul 13, 2002 at 08:27:23AM +0200,
> Wojciech Puchar <wojtek@chylonia.3miasto.net> wrote:
> > > > > snapshot for both windows and NetBSD. This
> should at least give us a
> > > > > hint why are we so slow.
> > > > >
> > > > > What I see is that single-sector read
> consists of
> > > > >
> > > > > 	command + 275us wait time + 150us data
> transfer time = 430us.
> > > > >
> > > > > Write, on the other hand, looks a bit
> different:
> > > > > 	command+150us data transfer+2850us wait
> time = 3000us
> > > > >
> > > > aren't these IDE-flash devices capable of IDE
> multisector?
> > > >
> > >
> > 
> >
>
--------------------------------------------------------------------
> > Charakterystycznymi cechami rozwoju oprogramowania
> jest wyk?adniczy
> > wzrost wymaga? sprz?towych, kwadratowy wzrost
> ilo?ci b??d?w, liniowy
> > wzrost ilo?ci bajer?w przy mniej ni? liniowym
> wzro?cie funkcjonalno?ci
> > 

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