how to identify bootable 4-bit, 3V SD cards?

(undoubtedly the first in a series of trivial questions as i'm
putting together an intro seminar on the beagleboard i'm planning to
present at least twice later this year, and i'm trying to anticipate
every possible question, including the ones *i* have. :slight_smile:

  assuming that you can still boot only off of a 4-bit, 3V SD card, is
there an easy way to identify those? even the people at the local
tech shop seemed puzzled when i asked if they had a way of telling
whether the card was either:

  * 4-bit, 3V, or
  * 8-bit, 1.8V (are those the only possibilities?)

  pawing through the selection of 2G cards, i found one -- a patriot
SD -- which had written on the back of the package buried in chinese
text the words "2.7 - 3.6V", which i'm *guessing* means a 4-bit card,
but i don't know enough about these things to be sure of that.

  and if one inserts a mystery SD card into a linux system, will that
info show up anywhere, maybe in /var/log/messages or under /proc
somewhere? thanks.

rday

I've been able to boot of every SD, SDHC and MMC card I have.

regards,

Koen

Robert P. J. Day wrote:

  assuming that you can still boot only off of a 4-bit, 3V SD card, is
there an easy way to identify those?

Any SD(HC) card is 3V, 4 bit.

  * 8-bit, 1.8V (are those the only possibilities?)

8 bit are only mmcplus/mmcmobile cards or some sort of embedded MMC like Samsung MoviNAND. And even those (except possibly embedded ones) can do 3V and 4 or 1 bit transfers. However the MMC protocol is a bit different from SD so maybe MMC cards can have some issues with bootloader code? In that case using SD (not MMC) card is safest bet.

Frantisek

then what does it mean when you read warnings that you *must* use a
4-bit, 3V SD card, like here?

http://www.beagleboard.org/irclogs/index.php?date=2008-09-18#T18:52:35

and i know i've read that warning in huge red letters elsewhere, i
just don't remember where. has anyone here failed to boot from SD
because they were accidentally using the wrong type of SD card?

rday

Robert P. J. Day wrote:
> assuming that you can still boot only off of a 4-bit, 3V SD card, is
> there an easy way to identify those?

Any SD(HC) card is 3V, 4 bit.

  ah, i was unaware of that. maybe i'd better take a few minutes and
read up on the technicalities of SD/MMC cards.

> * 8-bit, 1.8V (are those the only possibilities?)

8 bit are only mmcplus/mmcmobile cards or some sort of embedded MMC
like Samsung MoviNAND. And even those (except possibly embedded
ones) can do 3V and 4 or 1 bit transfers. However the MMC protocol
is a bit different from SD so maybe MMC cards can have some issues
with bootloader code? In that case using SD (not MMC) card is safest
bet.

  i'm thinking that's the sort of thing that should be included along
with the warning about SD card types, for people (like me :slight_smile: who
weren't sure what to *do* with that warning. thanks.

rday

Robert P. J. Day wrote:

Robert P. J. Day wrote:

  assuming that you can still boot only off of a 4-bit, 3V SD card, is
there an easy way to identify those?

Any SD(HC) card is 3V, 4 bit.

  ah, i was unaware of that.

AFAIK dual voltage was planned for SD standard but so far was not finalized in any revision of the standard (anyone knows why?) so there really is not another option for SD. Or do we talk about possible cards supporting voltage like 2.8V and not supporting 3V exactly? Don't think so, any card should do 3V, SD operating voltage is 2.7-3.6V.

MMCmobile/MMCplus are the ones who are realy dual voltage so they can do ~3V or switch to ~1.8V.

maybe i'd better take a few minutes and
read up on the technicalities of SD/MMC cards.

http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf
:slight_smile:

MMC was available [1] on www.mmca.com site too but I can't find it now, the site is pretty empty.

Frantisek

1. http://intr.overt.org/blog/?p=69