Didj Explorer SD Kernel

From eLinux.org
Revision as of 17:57, 16 December 2010 by Reggie (talk | contribs)
Jump to: navigation, search

Booting a didj using an explorer framebuffer kernel and rootfs from SD


working toolchain
the latest kernel sources for the leapster explorer
the latest erootfs obtained via lfconnect (from the lfps)
some patches (rcS, kconfig,makefiles, source code patches?)
A djhi or other means of connecting an SD/uSD card to a didj
a reasonable sized SD card partitioned with a Vfat partition and ext3 partition in that order (tested on a 2GB uSD, will probably work on 64MB but > 512MB is probably best)
a patched defconfig (goes in arch/arm/configs with the other lf1000 defconfigs)
lightning-boot 1.4 or the latest emerald boot or a modified lightning-boot (not essential but nice for testing)

This document lays out what I went through to patch the leapfrog explorer 2.6.31 kernel to work on a didj with the kernel and rootfs on an uSD card, you don't have to follow the whole article as I will wrap it all up in patches/source code but you may find it useful for reference for driver/module patching in the future.

Kernel Preparation

I based my defconfig on leapfrogs new arch/arm/lf1000_ts_fb_defconfig, simply running make clean then make lf1000_ts_fb_defconfig however you do not need to do this yourself if you are using my defconfig and supplied patches.

Patch the MMC/SD,ext3 and nand drivers

first thing we need to do is patch the MMC stuff, as it stands, you can put them in as built in but it will stall the kernel when it tries to bring everything up, if you leave it long enough it clears its issue (pending frags in the audio dma buffers?) but this doesn't help as the system doesn't bring up the other core mmc modules with the lf1000 stuff. The lf1000-mmc is obviously clashing with something so we need to look in the makefile, in the makefile we find that its been randomly placed in the list and looking at what leapfrog tend to do I simply moved the mmc object to the end of the list, which immediately cleared the kernel stalling issue :)

Now we've cleared the stalling issue we can get on to the rest of the mmc module bringup, it was suggested to me that I should try adding the lf1000, mmc block and ext3 modules to each others dependency lists in the respective kconfig file, having done this the lf1000 mmc driver now comes up correctly with the kernel :) use the supplied mmc patch to patch the relevant makefile and kconfig files.

Patch the cmdline in .config

thats the MMC drivers patched, but we need a custom cmdline configuration to actually see the rootfs partition on the SD card, this is taken care of in the deconfig that I've supplied:

CONFIG_CMDLINE="mem=16M root=179:02 rw rootfstype=ext3 rootdelay=2 debug=1 init=/sbin/init console=ttyS0,115200 ubi.mtd=Brio"

You'll notice that the cmdline is a bit sparse compared to the usual one, I've removed the mtd.ubi references as they are unecessary for this purpose and simply make the boot time longer as the nand driver tries to find non-existent partitions. I've patched the 2.6.31 nand driver to use the didj mtd partition layout and I improved nirvous fantastic original 2.6.31 didj kernel patch by patching the kconfig file to have use the same layout. use the supplied patch(es) to patch the nand driver and kconfig files.

This kernel *DOES NOT* automatically mount any didj partitions but they can still be accessed by the usual mount commands, the didj partitions are not necessary but I made the changes so they are accessible so that in theory you can rebuild a dead didj using just a djhi, lightning-boot1.4-uart and a prepared SD card. Be aware that whilst they aren't mounted the didj partitions can still be overwritten by the standard flashing tools that are supplied by leapfrog, you have been warned :)

Patch the buttons in the .config

thats the MMC and nand sorted but there is still a little way to go. we need to setup the buttons so that they are recognised correctly at boot time, this can be mostly achieved by setting


This fixes the majority of the button recognition but leaves the volume buttons unrecognised, however the volume slider does still work, the drivers need patching to complete this setup, that will be for a later update.

Patch the Framebuffer

We also need to patch the framebuffer settings, leapfrog very kindly supplied a newer framebuffer driver and a defconfig to go with it, I based my defconfig around this, unfortunately its setup for an explorer with 64MB of ram, fortunately its an easy fix, the start address is in the wrong place, in the defconfig I made the following change:


that's pretty much it for the kernel preparation, you can compile it now if you like, then all that is left to do is prepare the SD card and populate it.

Prepare and Populate the SD card

As previously mentioned, you will need a uSD card and a djhi, you can probably build this on a 64MB card but > 512MB would be much more sensible, I used a 2GB card.

Partition and format

You'll need to partition the SD card into 2 partitions, 1 vfat partition and 1 ext3 partition, the vfat partition needs to be first, its entirely up to you what size they are as long as the vfat partition is big enough to hold at least 1 kernel zImage (about 2MB) and the ext3 partition is big enough to hold a full rootfs (about 40MB).

Populate the partitions

Once the card is formatted you can now populate the partitions with the necessary files.

You will need the erootfs.ubi file mentioned in the prerequisites, once you've downloaded it you need to mount the image on your host PC, to mount the leapfrog erootfs.ubi file use this tutorial: How to Extract Files From the Firmware LFP file

Once you have the erootfs.ubi image mounted copy the contents onto your ext3 partition on the SD card, copy across the supplied patched files to the ext3 partition and copy your zImage to the vfat partition on the uSD card, if you are using the patched lightning boot then make sure you name your zImage appropriately (zImage or zImage2).

Test everything

If everything has gone smoothly you should be able to put the SD card into your djhi, start lightning boot and choose 'Load zImage from SD', you should see the counter increase in the bottom right corner of the screen, once it stops you should see the console start outputting as the kernel probes all the built in modules.


1. Leapfrog and my changes

Leapfrog have changed the way they do things now, most of the hardware stuff is created via the kernel module probing and mdev. Most of the /etc/init.d/rcS stuff was for communicating with leapfrog for updates or recovering from crashes, I have left it so you get a minimal boot, all of the networking stuff still works, you just have to do it by hand for now until we decide exactly what resources are necessary at boot up, we may well be able to do NFS boot on the didj via g_ether usb gadget drivers.

2. Mounting the /Didj nand partition and the mmc vfat partition

I've left the /Didj ubi.mtd=Brio partition in the cmdline, the nand drivers attach it for us, all you need to do is mount it if you need access to it, it will be on /dev/mtdblock8, unless you have an NHE cart in which case it will be on the mtd device named ubi_Brio, to find out which partition that is do:

cat /proc/mtd

Translate that to the appropriate mtdblocknumber and mount that device with the following (change the 8 to the appropriate number):

mount -tvfat -orw,noatime /dev/mtdblock8 /mnt2

You can mount the vfat partition on the didj with:

mount -tvfat -orw,noatime /dev/mmcblk0p2 /mnt

3. Mass Storage access for file transfer and kernel updates

I have written a pair of simple scripts to allow the vfat SD partition to be available over the g_file_storage module, this makes it act as if it were a usb stick in its own right. I have it configured so that I can plug in the usb cable, run the appropriate script and the drive automatically mounts on my dev box. This makes it very simple to update the kernel and transfer it to the device, run the disable script and reboot into your new kernel.

The scripts are called massenable and massdisable, to setup the didj so that it automounts on the host I have done the following on the didj:

# echo -e "ENABLED\nUNLOCKED\n" > /flags/usb_mass_storage
you can enable the mass storage by running:
# massenable
you can disable the mass storage by running:
# massdisable

at the moment it is only setup for the vfat partition but there is nothing to stop you using the existing script to learn how mount any partition on a host PC.

4. using the framebuffer

I have done minimal testing on the framebuffer, we get the tux logo and leapfrog have supplied a new app. called imager-fb, make sure you are using the correct mode, RGB 565,888, RGBA 8888 (16,24,32bit) via bits_per_pixel :

echo 24 > /sys/devices/platform/lf1000-fb/graphics\:fb0/bits_per_pixel
imager-fb /LF/Base/L3B_Art/UI_TitleSplash.png

should set the mode up for RGB888 and display the splash screen.

5. To Do

The volume buttons need sorting out so that the system recognises them properly at boot, as mentioned they work but still give a pin/port undefined error.

/dev complains about being in use when the system is rebooted/shutdown, I suspect this is because its mounted early on a ramdisk, I suspect its not a major issue as /dev is populated from a tar created on first boot of a new rootfs but it would be good to confirm.

We need to quieten down the messages the drivers send to the console, some of it is kernel/error messages which can be turned off via debug settings (I think) and setting log levels? in the kernel cmdline, but turning off some things that produce messages like CONFIG_LF1000_AUDIO_STATS breaks the driver.

Add code to lightning boot or emerald boot to allow booting from a simple text configuration file on the vfat partition, this will allow for simple CONFIG_CMDLINE changes that don't require recompilation of the kernel. This will be useful for the SD rootfs based kernels and normal didj/explorer kernels.