Is the RPI SD card clocking speed established at startup?

Currently the SD card slot is not using the maximum spec of the SD card.  There are people who have fixed this problem and are trying to get the foundation to incorporate the performance of the SD card into the next image.

See this: http://www.raspberrypi.org/phpBB3/viewtopic.php?p=91559 for more information.

I can not answer Q2 and Q3.  Sorry.

Hello Nick, that crashing sounds like it could be a power problem, rather than something to do with the SD card ? What is the spcfication of the charger you are using ?

Some of the early Pi's seem to be sensitive to heat as well, my first Pi needs power removed and a good rest before it will boot back up again (although doesn't crash), the second, later model is fine with all peripherals being the same as for the first.

Also check that your SD card is on the working list:http://elinux.org/RPi_VerifiedPeripherals#SD_cards

I've heard of people solving mysterious crashes by setting "vm.min_free_kbytes" to a larger value.  For example, here is a RasPi forum thread I found by searching for "min_free_kbytes" on the raspberrypi.org front page: http://www.raspberrypi.org/phpBB3//viewtopic.php?f=71&t=11445&start=25.

I've never tried this myself.

Thank you.  The link is very interesting.

Fergus Byrne wrote:

 

Currently the SD card slot is not using the maximum spec of the SD card.  There are people who have fixed this problem and are trying to get the foundation to incorporate the performance of the SD card into the next image.

 

See this: http://www.raspberrypi.org/phpBB3/viewtopic.php?p=91559 for more information.

As the instigator of that thread, I'll point out that most of the fixes are already incorporated in the current Raspbian image. In essence the driver now uses the maximum speed that the R-Pi hardware can support in combination with your card.

You're correct that this may not be the maximum the card can support, but this is largely due to the faster modes requiring the interface to run at 1.8v and the R-Pi only being capable of running the sd interface at 3.3v.

There's still work to be done - seems that some people are having data corruption problems.  The latest changes to try to sort that have recently been pulled, see https://github.com/raspberrypi/linux/pull/70 but this may take some time to appear in a released image. In the meantime you may get the updates uring the 'rpi-update' command if it's in your chosen distro. If it's not, get it here https://github.com/Hexxeh/rpi-update

Nicholas Toop wrote:

 

1. Is the SD card clock speed "discovered" by RPI at start up by it trying to find the fastest clock which works or is this speed fixed?

2. Does the working maximum clock rate for an SD card drop as it warms up?

3. I note that cooling the RPI SD card but not the RPI from a crashed RPI with freezer spray seems to make it much more likely the RPI will reboot successfully.

1. The card is interrogated at boot/card insertion, the card has some details of what it thinks it supports that the driver will make use of to work out what speeds to try. Eventually there's some tuning where the driver will attempt a speed and if it fails try another, usually slower, speed until it finds one that works.

2. Unlikely. Even so, the driver won't attempt to renegotiate the speed unless the card is removed, or possibly if there's an error and it tries to recover. If you follow through the threads Fergus linked to you'll see that once a 'working' speed has been chosen it tends to stick with it, even if that means it takes 30mins to boot..

3. Do you have some different cards you can try ?  One of the issues with sd cards is that there are many counterfeit cards, especially on places like ebay. So it's possible to get a card labelled as a 8GB class 10 card that in reality is a 2GB class 2. If the descriptor in the card has been modified then there's the chance you're effectively overclocking the card.

As others have said, check the wiki for compatible cards, get one from somewhere reputable.   As suggested by John several times elsewhere on this forum, the wiki troubleshooting section is always worth a read http://elinux.org/R-Pi_Troubleshooting