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Ok, now I want to compile the kernel on the Pi. Cross compiling is *much* faster, but since I plan to only make deltas to some driver files, I won't have to recompile every time. So bite the bullet now, get the object files on my Pi with my compiler, and then (hopefully) after 6-9 hours I can start doing some development on SPI drivers and/or an SAA1064 I2C driver.

So, using the magic of Google, found out what packages I need from here. I'm pretty sure I already have some of them, but what the heck:

Code:

sudo apt-get -y install libncurses5-dev fakeroot wget bzip2 build-essential

Turns out all I needed was libcurses5-dev - the others were already there.

Now grab bootc's kernel branch. This will actually get everything there, including the mainline and such. Takes a lot more time, but will allow me to contribute patches back to him if I want to in the future.

Code:

cd
mkdir raspi
cd raspi
git clone https://github.com/bootc/linux.git

This failed the first time because I don't have enough memory on my Pi to decompress what I get from github. I will probably run into problems while compiling too. Hmm.

Try adding swap partition:

Code:

sudo fdisk /dev/mmcblk0         #create swap partition, type 82
sudo reboot
sudo mkswap /dev/mmcblk0p3
sudo swapon /dev/mmcblk0p3
vi /etc/fstab                   # uncomment the swap mount point

...

Well, the 2GB SD card I started with was getting a bit cramped. So I bought an 8GB one, and transplanted by filesystem.

First, I used Win32 Disk Imager to read the 2GB SD card onto a new image on my Windows desktop. Then I popped in the 8GB card and wrote the image to it.

I booted the Raspberry Pi with it, and I still had the 2GB images (this was expected). I then followed the instructions here, and they worked perfectly.

Next I'm going to compile the kernel on the Pi. Cross compiling is faster, but I will end up doing small changes and relinking a lot, so it may be tolerably fast once I get it compiled once. We'll see :-)

Well, the bug I found in my last blog post was found by someone else (and fixed commit1 commit2 ) in bootc's kernel branch (not in the official one though, sadly).

So here is how I updated stuff and tested.

First, update the firmware using the rpi-update tool installed previously:

Code:

$ sudo rpi-update
$ sudo reboot

Then install new kernel and give it a try:

Code:

$ wget http://apt.bootc.net/debian/pool/main/l/linux-source-3.2.21-rpi1+/linux-image-3.2.21-rpi1+_2_armel.deb
$ sudo dpkg -i linux-image-3.2.21-rpi1+_2_armel.deb
$ rm !$
$ sudo cp /boot/vmlinuz-3.2.21-rpi1+ /boot/kernel.img
$ sudo reboot

Now, try the stuff we did before. Load up the i2c-dev driver and manually configure the I/O expander using the sysfs mechanism:

(as root)

Code:

# modprobe i2c_dev
# echo pca9535 0x20 > /sys/bus/i2c/devices/i2c-0/new_device
# dmesg | tail -2
 
 
[  272.400789] i2c i2c-0: new_device: Instantiated device pca9535 at 0x20
[  272.440470] pca953x 0-0020: interrupt support not compiled in

Yay! No error!

Code:

$ cd /sys/class/gpio/gpiochip240
$ cat label base ngpio
 
 
pca9535
240
16

It auto-sets the range of gpios! The default number for ARCH_NR_GPIOS is 256, so I guess it is counting backwards as it tries to find a range.

Try to actually allocate ...

The end of my last post ended with this:

Code:

root@raspberrypi:~# echo pca9535 0x20 > /sys/bus/i2c/devices/i2c-0/new_device
root@raspberrypi:~# dmesg | tail -4
[ 1007.458897] pca953x 0-0020: interrupt support not compiled in
[ 1007.458931] gpiochip_add: gpios -1..14 (pca9535) failed to register
[ 1007.458990] pca953x: probe of 0-0020 failed with error -28
[ 1007.459029] i2c i2c-0: new_device: Instantiated device pca9535 at 0x20

Well, now I know why this doesn't work.

Update: Everything below is sort of wrong. The sequence is correct, but it turns out the default behavior is to search for an open range of gpios to assign the I/O expander (file drivers/gpio/gpiolib.c, function gpiochip_find_base). However, the system constant ARCH_NR_GPIOS (set in arch/arm/mach-bcm2708/include/mach/gpio.h) on the Raspberry Pi is set to the number of I/Os on the BCM2708 chip, NOT the number of I/Os available for the kernel to assign. So when gpiolib tries to find an open gpio range, it can't find anything, and fails. This is a bug in the platform support code from the Raspberry Pi guys, and makes it not possible to load drivers for I/O expanders (at least ones that use the gpiolib framework).


The Linux I2C framework has several ways to "instantiate" a device and load it into the system (see here). The one we are using above is "Method 4: Instantiate from user-space". This has the benefit of being very ...

So I am using the same setup for the PCA9535 as my previous post. Using the Raspberry Pi I/O expander diagram, I wired up my PCA9535 to the Raspberry Pi.



When it starts, I log in, become root, and start to play. Install i2c-tools:

Code:

sudo apt-get -y install i2c-tools

Now if I try to detect, it doesn't work:

Code:

i2cdetect -l

Just gives blank output.

Load up the i2c-dev kernel module:

Code:

modprobe i2c_dev

Now i2cdetect shows us something:

Code:

root@raspberrypi:~# i2cdetect -l
i2c-0   i2c             bcm2708_i2c.0                           I2C adapter
i2c-1   i2c             bcm2708_i2c.1                           I2C adapter
root@raspberrypi:~# i2cdetect -y 0
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Now try some low-level stuff on the bus directly, not using a driver. When the thing powered on, the interrupt light turns on. I have to read locations ...