Repeater and CFC

[don.goodeve@home.com]

Dear Loopers

Disclaimers: 
------------------------------------------------------------------------
1. The following is based on my experience and is my personal 
    opinion. It should not be taken to represent the official views 
    or position of Electrix/IVL Technologies. (even though the
    conclusion is pretty much exactly the same).

2. The following only relates to CFC cards in the context of
    their use with Repeater, and implies nothing about their
    suitability or performance with ANY OTHER PRODUCT.

3. If you think I am being paranoid, I have been flamed badly
    in the past. All this having been said, flame proof underpants
    on and here goes...
-----------------------------------------------------------------------

I noticed the discussion starting around CFC buys. There is some 
stuff on the Electrix website, and also on a flyer shipped with the 
unit. However you do need to be aware of card specs - the only
real way to know things are going to be cool is to test Repeater
with the card you wish to use. Until specifications become a
perfect art, rather than a marketting tool, that is just the way it
is.

Electrix has been doing a lot of testing with different CFC cards,
and our recommendations are based on the results of those
tests.

Technobabble follows
---
CFC card specs that are published from different manufacturers 
seem to cover the following:

Burst-mode rate (quoted ~6-10MB/sec). Ignore this. Unfortunately 
everyone who designs a CFC interface needs to design for the 
lowest common denominator anyway, making this spec worse than 
useless IMHO.

Read rate. Typically 800KB/sec -> 2MB/sec. Read rate is not
really the issue. Reading flash memory is pretty damn quick and
in Repeater accounts for a fairly small proportion of the time 
consumed at the CFC interface.

Write rate. Quoted (ahem!) 500KB/sec -> 1.5MB/sec. However
this is the long-term sustained rate, and depending on the card
manufacturer, the data caching algorithms they use, and a whole
load of other variables the short-term variance in write operation 
latency can be huge. I know - I have pored over the logic analyser 
and scope traces looking into this phenomenon until I went bug 
eyed [still in recovery...].

CFC cards do some pretty nifty footwork under the hood to manage 
the storage medium - including error recovery, bad sector
remapping, wear levelling etc... Also, writing is a cached 
mechanism and there are additional time effects due to the caching
scheme used, the pattern of writes to the card and the amount of 
cache available.

The result of all of this is that an apparently fast card may 
occasionally (or in the case of one card we tested, very often...) 
take a long time to complete a write operation. Hit a few of these 
long write operations in a row and all of a sudden Repeater will 
have run out of write buffer space and will inform you that there is 
an issue here...

Most cards will handle the 'sequential' writing of mono operation 
with no problems. Stereo operation is where most problems lie. 
The pattern of writes to two .wav files can fight with the CFC 
caching scheme and cause the card performance to be somewhat 
less than desirable. 

So - that is the low down.
---

My advice is to read the specs (the faster card manufacturers will 
quote them with pride. The slower card manufacturers will quote 
them under a subtle disguise to make you think they are better 
than they are...). Take all specs with a healthy dose of reserve.

Then, if you can test a card before you buy, do. We are providing 
information on cards we have thoroughly tested and are happy with 
to help with purchase decisions. 

The Simple Technologies cards deliver. DaneElec also are just 
dandy. This does not imply that other cards out there will not
also do just fine, but it provides a starting point. I hope that with
experience that this forum will provide more information about
good card choices for use with Repeater. We will also update
the information on the web site as more experience and test
results become available.

Please consult the website and feel free to post questions
for us folks about CFC cards. We will be happy to occasionally 
break the lurking mode and provide what information we can.

Cheers, and I hope you folks have a *lot* of fun...

        Don Goodeve

(of Rik Elswit's 'Don and the Maniacs' fame... I kind of like that 
one...)

ps. CFC technology is moving *damn* quick these days, and the 
speed of cards will become less of an issue as time goes on. With 
Repeater we had to design towards where we expected CFC 
technology to be, and fortunately our Crystal Ball did a pretty good 
job.
 ----------------------------------------------------
|Don Goodeve                                         |
|Brentwood Bay, BC, Canada                           |
| don.goodeve@home.com                               |
 ----------------------------------------------------
'As if you could kill time without injuring eternity'
  (still my favourite H.D.Thoreau quote - after all
   these years...)