Is the RPI SD card clocking speed established at startup?

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

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