AT91 kernel programming documentation ?

AT91 kernel programming documentation ?

[Stefan Schoenleitner]

Hi,

I'm looking for some good documentation concerning AT91 Linux kernel development.
Currently I have a Olimex AT91SAM9260 development board which is supported by
the at91 patch set.
Now I would like to add different hardware to the board and write some kernel
code for it.
Unfortunately, there doesn't seem to be a lot of documentation.
At the moment I'm reading mach-at91 related source code and trying to find out
how things work.

Specificly, I would like to know how the different SoC devices can be accessed
and used, how I can do port multiplexing, how I can tell the kernel which
hardware is attached to where and so on.

Can you guys suggest any documentation ?

Re: AT91 kernel programming documentation ?

[Robert Schwebel]

On Wed, Jul 30, 2008 at 03:53:19PM +0200, Stefan Schoenleitner wrote:
> I'm looking for some good documentation concerning AT91 Linux kernel
> development. Currently I have a Olimex AT91SAM9260 development board
> which is supported by the at91 patch set.

The base functionality is supported in the Linux mainline.

> Now I would like to add different hardware to the board and write some
> kernel code for it.

What kind of hardware?

> Unfortunately, there doesn't seem to be a lot of documentation. At
> the moment I'm reading mach-at91 related source code and trying to
> find out how things work.

I assume you've already bought a copy of the Rubini Device Driver book?

> Specificly, I would like to know how the different SoC devices can be
> accessed and used, how I can do port multiplexing, how I can tell the
> kernel which hardware is attached to where and so on.

Check arch/arm/mach-at91/*. It very much depends on what you want to do.
Documentation/drivermodel/ might also be worth a look.

rsc
-- 
 Dipl.-Ing. Robert Schwebel | http://www.pengutronix.de
 Pengutronix - Linux Solutions for Science and Industry
   Handelsregister:  Amtsgericht Hildesheim, HRA 2686
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Re: AT91 kernel programming documentation ?

[Stefan Schoenleitner]

Hi,

Robert Schwebel wrote:
> [...]
> 
>> Now I would like to add different hardware to the board and write some
>> kernel code for it.
> 
> What kind of hardware?

An audio codec (TLV320AIC23B) connected to the I2C and I2S (over Atmel SSC) bus.
There seems to be a codec driver already (drivers/media/video/tlv320aic23b.c)
though it looks like I'll have to modify the driver a bit to support other
sampling rates as well.
Currently my first goal is to get the audio codec up and running so that it
works with ALSA.

Then I would like to add two SPI devices as well.
Since most of the chipselect lines are already used I was thinking of using a
demultiplexer which is supported by the AT91SAM9260.

Due to the fact that the board will be a custom design, I guess I will also have
to write a board implementation (i.e. arch/arm/mach-at91/board-<myboardname>.c)
so that the kernel for example knows which ports are used for communication
buses on the pins.

Reading the source code already shed a little light on how things are done.


> 
>> Unfortunately, there doesn't seem to be a lot of documentation. At
>> the moment I'm reading mach-at91 related source code and trying to
>> find out how things work.
> 
> I assume you've already bought a copy of the Rubini Device Driver book?

I read various papers and kernel documentation, parts of it also being from the
second edition of the book.
However, I just saw that there's a newer (third edition) available.
It's online under a CC license: http://lwn.net/Kernel/LDD3/

However, although the book gives a good intoduction on writing drivers, it seems
to miss some parts like SPI, I2C, board implementation and such.
IMHO the best way is to use the book as reference for driver implementation and
to read the existing AT91 kernel code.

>> Specificly, I would like to know how the different SoC devices can be
>> accessed and used, how I can do port multiplexing, how I can tell the
>> kernel which hardware is attached to where and so on.
> 
> Check arch/arm/mach-at91/*. It very much depends on what you want to do.
> Documentation/drivermodel/ might also be worth a look.

arch/arm/mach-at91 is where I looked at the source most of the time.
However, I didn't notice Documentation/drivermodel until now.
Thank you for mentioning it.

Book about embedded-type device drivers

[Thomas Petazzoni]

Le Fri, 01 Aug 2008 08:36:49 +0200,
Stefan Schoenleitner <dev.c0debabe@gmail.com> a écrit :

> I read various papers and kernel documentation, parts of it also
> being from the second edition of the book.
> However, I just saw that there's a newer (third edition) available.
> It's online under a CC license: http://lwn.net/Kernel/LDD3/

The 3rd edition is certainly newer than the second, but starts to be
quite old. It has been written against the 2.6.10/2.6.11 kernels.

> However, although the book gives a good intoduction on writing
> drivers, it seems to miss some parts like SPI, I2C, board
> implementation and such. IMHO the best way is to use the book as
> reference for driver implementation and to read the existing AT91
> kernel code.

In addition to « Linux Device Drivers », a good book is « Essential
Linux Device Drivers », from Sreekrishnan Venkateswaran, available at
Prentice Hall. This book is very recent (April 2008).

  1. Introduction
  2. A peek inside the kernel (timers, concurrency, memory, etc.)
  3. Kernel facilities (threads, helper interfaces)
  4. Laying the groundwork (IRQ, device model, memory barriers, etc.)
  5. Character drivers
  6. Serial drivers (including TTY drivers and line discipline drivers)
  7. Input drivers (evdev interface, serio, keyboard, mice, touch
     controllers, accelerometers, etc.)
  8. I2C (I2C core, EEPROM driver, RTC driver, i2c-dev, SPI, 1-wire)
  9. PCMCIA and Compact Flash
 10. PCI
 11. USB
 12. Video drivers (frame buffer, console drivers)
 13. Audio drivers
 14. Block drivers
 15. Network interface cards
 16. Linux without wires (Bluetooth, Infrared, Wifi)
 17. MTD
 18. Embedded Linux
 19. Drivers in userspace
 20. More devices and drivers
 21. Debugging device drivers
 22. Maintenance and delivery
 23. Shutting Down

I'm at the end of chapter 8, and until now, it's really good.

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers and embedded Linux development,
consulting, training and support.
http://free-electrons.com

Re: Book about embedded-type device drivers

[Markus Franke]

Hi,

Thomas Petazzoni schrieb:
> In addition to « Linux Device Drivers », a good book is « Essential
> Linux Device Drivers », from Sreekrishnan Venkateswaran, available at
> Prentice Hall. This book is very recent (April 2008).

thank you very much for the hint. LDD3 is indeed a bit outdated and I 
also missed a chapter about I2C device driver development.

Best regards,
Markus