FAQ (SBC-i.MX51)

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Frequently Asked Questions for the SBC-i.MX51

Q: I've plugged in my SBC the first time, and after a while, it seems dead. What's the matter?

A: The first boot of the SBC Gnome image may take several minutes, because there are a lot of post-installation tasks to be run. Don't worry if the HDMI-connected screen gets blank -- as soon as the Gnome login screen loads, the screen will unblank automatically. Unblanking the screen with mouse or keyboard is not possible as long as the USB kernel modules are not loaded. Note that subsequent boots are faster.

Update: Since release 0.9, USB support is compiled into the Linux kernel and is therefore loaded earlier. So you can unblank the screen with a key press during configuration.


Q: What is the easiest way to disable gdm, the Gnome Display Manager, at startup?

A: Provide the kernel argument text at startup, i.e. add it to the -c switch of the exec command in Redboot.


Q: Why is the Linux kernel not able to mount the rootfs on the SD card? Boot stops with the error message "VFS: Cannot open root device "mmcblk0p1" or unknown-block(2,0)".

A: Likely, the kernel wanted to mount the rootfs before it detected the SD card. It's easy to solve however: Supply the kernel argument rootdelay=1 in Redboot. The argument tells the kernel how many seconds to wait before trying to mount the rootfs.


Q: Can I manually blank or unblank a frame buffer screen?

A: Yes, you can. There's a sysfs entry for each frame buffer: /sys/class/graphics/fbX. To blank e.g. fb0, type the following:

echo 1 > /sys/class/graphics/fb0/blank

To unblank fb0, type the following:

echo 0 > /sys/class/graphics/fb0/blank


Q: Why do I get a lot of ...time stamp is in the future warning messages while Linux boots?

A: The SBC-i.MX51 does not have a coin cell installed by default, so the RTC of the MC13892 PMIC cannot keep the correct time while the board is powered off. However, the default image starts the NTP (Network Time Protocol) at startup, which tries to synchronize the clock via the Internet.


Q: Why does Linux boot seem "hanging" if I mount the rootfs via NFS?

A: Likely, you forgot to disable eth0 network configuration in /etc/network/interfaces. See here how the target network setup works.


Q: My board reboots suddenly. Where's the problem?

A: We saw this behavior if the power supply is not powerful enough. Check your power supply if it delivers the correct voltage (try 12V). If it has a current limiter, disable it or set the maximum current.


Q: I get the error message "The network manager could not find some resources" if I log in to Gnome. What's wrong?

A: We tracked down this problem and are now using the .tar.bz2 and not the .jffs2 image for NAND flash setup (Gnome image). Release 0.9 (and the scripts coming with it) takes care of this issue, but your board obviously came installed with release 0.2, where this issue was not yet fixed.


Q: How can I interrupt RedBoot before it executes the boot script? I want to change the RedBoot configuration.

A: Use the serial terminal. Press the SBC's reset button and send [ Ctrl-c ] continuously to the serial terminal until RedBoot stops.

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