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Re: [microblaze-uclinux] Getting Started with microblaze-uclinux-gcc

Jose,
I'm also new to working with Linux/uClinux kernel modules and been stumbling my way through to getting something working the last week. My approach is to build my module parallel to the xgpio driver in the uClinux build tree using it as a template for a functioning Xilinx specific kernel module. The steps I followed are below. 

The xgpio module header lives at:

  uClinux-2.4.x/include/linux/xgpio.h

My xilinx module header lives at:

  uClinux-2.4.x/include/linux/xmotor.h

The xgpio module source lives in the directory:

  uClinux-2.4.x/drivers/char/xilinx_gpio

My xilinx module source lives in the directory:

  uClinux-2.4.x/drivers/char/xilinx_motor
I copied the Makefile and adapter.c file the xgpio module source into my source directory and stripped the gpio hardware specific code from adapter.c and renamed it xmotor.c. Other changes included making my own test IOCTL handlers ans such. My header file xmotor.h was also edited as needed and the module assigned a non-conflicting minor device number. I then made the minor changes in the Makefile in my source directory to account for the name changes of the files it should compile.
Next, I edited the following Makefile in the directory above my source directory: 

  uClinux-2.4.x/drivers/char/Makefile

To add the following just before the GPIO section:

  # Support for Xilinx MOTOR driver
  mod-subdirs += xilinx_motor
  subdir-$(CONFIG_XILINX_MOTOR) += xilinx_motor
  obj-$(CONFIG_XILINX_MOTOR) += xilinx_motor/xilinx_motor.o

Next, I manually edited the uClinux build .config file:

  uClinux-2.4.x/.config

And appended my own entry:

  CONFIG_XILINX_MOTOR=y

Finally, I edited the following file:

  uClinux-dist/vendors/Xilinx/uclinux-auto/Makefile
to include the following just before the 'ifdef CONFIG_XILINX_GPIO' section to create a device file for my module: 

  ifdef CONFIG_XILINX_MOTOR
  DEVICES +=      \
          motor,c,10,186
  endif
The from the uClinux-dist directory I did a 'make clean; make dep; make' compile and had the beginnings of a functioning module compiled into resulting uClinux binary image. Once I got the skeleton working at the 'Hello World' level I then started adding in my own hardware specific code and such. The hardest part so far for me was getting the interrupt handler working -- but I looked at the following file for a working example: 

  uClinux-2.4.x/arch/microblaze/kernel/xmbserial.c
Of course, I also created a test application that opens up my device and calls the various test IOCTL calls.
There are probably better ways of doing this, but so far this approach is working for me in getting uClinux to talk with my specialized FPGA IP. 

I hope this information is useful.

Mike Thompson


Jose Torres wrote:

Hello,
I have been scouring the internet for information on
microblaze-uclinux-gcc and kernel modules. I haven't come up with much
and any guidance would greatly be appreciated.

I have found two books and I was wondering if anyone with experience
with them recommend I buy them.
http://www.amazon.com/Building-Embedded-Linux-Systems-Yaghmour/dp/059600222X http://www.amazon.com/Linux-Device-Drivers-Jonathan-Corbet/dp/0596005903/ref=pd_bxgy_b_img_b/104-2097690-1463950 

A major problem that I am running into is where to locate the header
files available to me.

From what it seems, the compiler uses this directory:
PetaLinux\tools\linux-i386\microblaze-uclinux-tools\microblaze-uclinux\include 

I would like to incorporate the header files that the EDK provides to
me to allow access to hardware such as xgpio.h and xtmrctr.h.

From my understanding, I cannot utilize these functions in user mode

and must use a module to access kernel mode.

I have tried compiling a simple kernel module as follows:

#include <linux/module.h>

int init_module()
{
       printk("Hello...\n");
       return 0;
}

void cleanup_module()
{
       printk("World...\n");
}

But it simply will not make:
[bleep@localhost KernelMod]# make
microblaze-uclinux-gcc   -msoft-float -mxl-pattern-compare
-mno-xl-soft-mul -mxl-barrel-shift -mno-xl-soft-div -Wl,-elf2flt -o
KernelMod KernelMod.o
KernelMod.elf2flt: In function `_start':
KernelMod.elf2flt(.text+0x44): undefined reference to `main'
KernelMod.elf2flt: In function `init_module':
/home/bleep/PetaLinux/software/user-apps/KernelMod/KernelMod.c(.text+0xe8):
undefined reference to `printk'
KernelMod.elf2flt: In function `cleanup_module':
/home/bleep/PetaLinux/software/user-appsKernelMod/KernelMod.c(.text+0x114):
undefined reference to `printk'
/home/bleep/PetaLinux/software/user-apps/KernelMod/KernelMod.c:11:
undefined reference to `main'
collect2: ld returned 1 exit status
make: *** [KernelMod] Error 1

I hope this isn't a big problem and that I'm just oblivious to something.
Thanks,
Jose
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