[Elphel-support] CFAST cards with SATA adapter compatible

[Andrey Filippov]

Sebastian,

I just replied Carlos and wrote that the only problem with SATA devices was
with the old  SSD made actually from the CF cards. Adapter is transparent,
so if the CF card does not work in the camera directly, it will not work
with the adapter.  For slow applications it is possible to disable DMA in
the camera (needs adding the lying card to the blacklist and recompiling
the software).

Devices support some of 3 modes:

1) PIO (slow and loads CPU a lot)
2) DMA - fast
3) UDMA - even faster
Most CF cards support only 1 and 3 and respond as if they support 2 also
ETRAX processor has a bug in implementation of the UDMA, so UDMA is
disabled, that means that in the camera we only have 1 and 2. When the
camera detects the disk, it loads the device capabilities (1,2,3), and
selects the fastest it can support - 2. But here the lie of the CF card
controller comes to the light - and the camera fails to communicate with
the disk. There is a black list of those untruthful cards in the driver, we
already added some cards there -
http://elphel.cvs.sourceforge.net/viewvc/elphel/elphel353-8.0/os/linux-2.6-tag--devboard-R2_10-4/drivers/ide/ide-dma.c?view=markup

 Axis engineers said that it is possible to mitigate that bug and gave some
hints how to do that, but we never worked on it ourselves and it is
probably not too easy - otherwise Axis people would do it themselves. But
if anybody with the driver development skills would volunteer - we would
definitely love that and support such project.

Andrey


On Sat, Feb 4, 2012 at 11:53 AM, Sebastian Pichelhofer <
sebastian.pichelhofer at gmail.com> wrote:

> Do you think that http://en.wikipedia.org/wiki/CFast#CFast CFast Cards
> could work with this adapter:
>
> http://www.amazon.de/exec/obidos/ASIN/b003r4ifmg/geizhals1-21/ref=nosim?m=A3JWKAKR8XB7XF
> connected to the Elphel camera over SATA.
>
> To my understanding the card itself acts like a drive and needs no
> controller chip betweencard and camera that could lead to running into
> the UDMA issues again. But the card itself might use UDMA... ;)
> Any educated guesses?
>
> Regards Sebastian
>
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>
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