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Subject: Re: SD Card BUS royalties on a new hardware

Re: SD Card BUS royalties on a new hardware

From: john cooper <>
Date: Fri, 10 Apr 2009 11:44:34 -0400

Paul Louden wrote:
> Jonas Häggqvist wrote:
>> No one said using SD is a bad idea. What *was* said, was that having
>> *only* an external SD slot is a bad idea. We're suggesting you have
>> some internal storage - which could be as little as 64MB - for storing
>> Rockbox and the related files, and booting from.
>> Do you really not see that having Rockbox on removable storage is a
>> problem?
>> The Rockbox build, themes, settings, highscores etc will be on the SD
>> card, and you will have to copy these things back and forth or live
>> with everything changing and having to reboot each time you swap the
>> SD card.
> Maybe as much as 1GB of internal storage would be good, if one idea is
> to "share" music. If you have an SD card and no appreciable internal
> storage, you can't actually share. You may as well simply swap players,
> since there's no way to combine collections. If you have internal
> storage, you can copy appropriately licensed music off their SD card,
> then once you re-insert yours, add it to it.

The other issue which I had started to reply to was
SD is becoming (perhaps has become) a viable choice
for embedded flash usage. The issue being unmanaged NOR
flash gets expensive as effective capacity increases.
Moving to NAND flash has its own issues. Even if you
aren't impacted by the loss of direct instruction
execution with NAND, ECC becomes an issue. Not so
much for the SLC devices as the required ECC strength
is modest and as is the computational complexity of the
ECC algorithms. MLC NAND is quite attractive from a
low cost storage perspective. But it is a different
beast and requires stronger error correction with the
associated algorithms are (IIRC) at least O^2 dependent
on data size resulting in very limited throughput in
software based schemes.

You probably can't find any currently manufactured
flash <whatever> card which isn't MLC NAND. Flash
controllers have pushed the error management issue
into a hardware solution resulting in throughput
essentially becoming a non-issue.

So unless you are able to economically fit in NOR
flash, NAND is going to be the solution. And except
for the case of SLC NAND with software error correction
you are looking at specialized hardware to deal with
NAND management. My point here being is SD wraps up
MLC NAND + hardware management into a unified solution
at a mass market price point. SMD packaged surface
mount SD devices as well exist. So in the case your
widget is supporting an external user accessible SD
media slot, a scheme will already exist to communicate
with SD. Adding on-board SD would therefore pose no
added interface requirements on the system.


Received on 2009-04-10

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