
                  README for ARM based OMAP processor from TI
                  ===========================================

This is the README for Linux 2.6 on ARM based TI OMAP processors.

In the first section it gives some general hints how to start with OMAP Linux.
 
When successfully build a OMAP Linux kernel with help of first section and no 
bootloader is already on the board, section 2 gives some tips how to use
commercial JTAG tools. 

In March 2004 the Linux Kernel 2.6 for ARM based TI OMAP processors was cleaned.
The goal was to send clean patches to RMK's official ARM tree and to make it 
easier to add new OMAP processors or boards to the kernel tree. To keep the
kernel tree clean now, this document describes also some steps how 
to add code for a new OMAP processor or OMAP based board to the OMAP Linux 2.6 
kernel tree. This is what the third section of this document is about.

Section 4 of this README reports some rules to be followed to write 
clean code to make it ready for easy inclusion into public OMAP Linux kernel.

For more information also see TI's 'Linux Community for Texas Instruments OMAP
Processors' web page:

http://linux.omap.com

There, various downloads and resources can be found (e.g. documentation how
to build the kernel, how to use u-boot with OMAP Linux, pre-built tool chain
etc.).

The mailing list for OMAP Linux is hosted there, too:

http://linux.omap.com/mailman/listinfo


1. General hints how to start with OMAP Linux
--------------------------------------------------------------

The minimal setup is a arm-linux-gcc cross compiler, make, and some editor.
You will also most likely need a JTAG to flash the bootloader for the first
time.

The first step is to get a bootloader for your board, u-boot is the
recommended one:

http://www.denx.de/en/Software/GIT

Then you need to compile it with the same cross compiler as you would use
for the Linux kernel. Then you need to flash it to the board either via the
serial port, or by using a JTAG.

Once you have the bootloader running, you can compile the kernel.

You can get the OMAP sources either from the OMAP GIT tree, or by
applying patches. The OMAP GIT tree has the most up to date sources
and is the recommended one.

- Using GIT and cloning OMAP GIT tree please follow the README at:

http://www.muru.com/linux/omap/README_OMAP_GIT

Hint: If you are sitting behind a firewall and have to use a proxy for 
internet access, you can access GIT by http by setting the
http_proxy envirionment variable:

http_proxy=http://proxy_username:proxy_password@proxy_name:proxy_port/

If you use bash shell, then this might look like:

export http_proxy=http://foo:123@abc.host.com:8080/

with:

foo: Your user name for the proxy
123: Your password for the proxy
abc.host.com: The name of your proxy you use for internet access
8080: The port used on to access the proxy


- Using Patches:

If you don't want to use GIT, then you can do the same thing with patch.

Download the latest OMAP Linux patch from:

http://www.muru.com/linux/omap/

Get a matching Linux kernel from:

ftp://ftp.kernel.org/pub/linux/kernel/v2.6/

For example, if you download Linux-2.6.4-omap1 from muru.com, then you need
linux-2.6.4 kernel from kernel.org:

$ wget ftp://ftp.kernel.org/pub/linux/kernel/v2.6/linux-2.6.4.tar.bz2
$ tar xjf linux-2.6.4.tar.bz2
$ cd linux-2.6.4
$ cat ../Linux-2.6.4-omap1 | patch -p1

Note: If OMAP patch from muru.com is against a kernel release candidate, 
marked by -rcX, then kernel can be found on kernel.org under v2.6/testing/

Now, if you have a local kernel tree, either by GIT or by patch, you
should look into arch/arm/configs/ to see which of the various omap_xxx
configurations there you want to use. For example, if you have a OMAP1510
based Innovator board, you select omap_innovator_1510_defconfig by 

$ make omap_innovator_1510_defconfig

at top level directory (linux-2.6.4 in the example above).

Then you can compile the kernel with

$ make vmlinux

Or make Image or make zImage or make uImage.

Once you have the kernel compiled, you can upload it to the board via serial
port or JTAG (see below).

Then you need a root file system either as initrd or on the flash.

Once you have the system booting to Linux, you can use pretty much any Linux
applications cross compiled for ARM.


2. JTAG usage
--------------------------------------------------------------

If the flash of your board is really 'empty' and no bootloader is on the board
(e.g. u-boot) then you need a JTAG connection. With JTAG you can write
a bootloader to board's flash or download OMAP Linux kernel. For OMAP
commercial JTAG tools are available, so you have to pay for it.

Examples are TI's Code Composer Studio (CCS) or Lauterbach's TRACE32 JTAG.

- Linux kernel download with CCS

You can use CCS to directly load an ELF file to your board. For example, use  
arch/arm/boot/compressed/vmlinux. zImage isn't suited because it is not an ELF
file. CCS looks for .out files, so copy arch/arm/boot/compressed/vmlinux 
to vmlinux.out and load it using CCS. Or use the filter *.* to select
vmlinux directly. Remember to run arm-linux-strip on ELF file first as CCS 
get stroppy about unstripped ELF files.

If you want vmlinux to be linked to run at a specific address, you can use 
the CONFIG_ZBOOT options in the kernel build. But first try without
CONFIG_ZBOOT as the compressed image should be able to run from address
zero (if your CCS .gel files map address zero.)

Otherwise, use something like this:

CONFIG_ZBOOT_ROM=y
CONFIG_ZBOOT_ROM_TEXT=10408000
CONFIG_ZBOOT_ROM_BSS=10800000

Also note that CCS is pretty useless for debugging Linux as it doesn't
properly handle virtual memory. In other words, once the MMU is
turned on and Linux is using virtual memory, CCS can no longer
properly disassemble, set breakpoints or read memory.


- Linux kernel download with Lauterbach TRACE32

To be done.


3. How to add new processor or board to OMAP Linux kernel tree
--------------------------------------------------------------

It is assumed that the OMAP processor to be added is based on an already 
supported ARM core (e.g. ARM925 or ARM926). How to add support for new ARM 
processor core that is not supported by ARM Linux is not scope of this document.

1. If a new OMAP processor should be added, identify the ARM core of this 
processor. E.g. at time of writing this document in March 2004 OMAP730 (ARM926 
core), OMAP1510 (ARM925 core) and OMAP1610 (ARM926 core) are supported.

For a new board or device, identify the OMAP processor on the board. E.g. at 
time of writing this document in March 2004 four boards are supported: 
Innovator1510 (OMAP1510 processor), Innovator1610 (OMAP1610 processor), 
Perseus2 (OMAP730 processor) and H2 (OMAP1610 processor).

Please refer http://www.muru.com/linux/omap/ to get latest information on the
list of boards supported.

/* Discussion needed: How to handle the tons of compatible processors? 
E.g. what to do if OMAP16xx is mainly identical with OMAP16yy? */

2. Start with arch/arm/mach-omap[1/2]/Kconfig and add a new processor or board
option.

To add a new processor add a new config option to the "OMAP Core Type" choice. 
See examples for the syntax. The config option has to be called "ARCH_OMAPxxxx" 
where xxxx is the number of OMAP processor. Don't forget to select a existing
clock frequency or to add a new one in "OMAP Feature Selections" section for
your new processor. 

To add a new board or device, add a new config option to the "OMAP Board Type" 
choice. See examples for the syntax. The config option for boards has to be 
called "MACH_OMAP_yyyy" where yyyy is the board name. Don't forget to add a 
short help.

Note: Kernel 2.6 Kconfig system will automatically expand the configuration 
names with a leading "CONFIG_". So "ARCH_OMAPxxxx" will be expanded to 
"CONFIG_ARCH_OMAPxxxx" and "MACH_OMAP_yyy" will expand to 
"CONFIG_MACH_OMAP_yyyy". In code this can then be used by macros like 
"#ifdef CONFIG_ARCH_OMAPxxxx" and "#ifdef CONFIG_MACH_OMAP_yyyy".

Note: How to handle boards which are compatible or extensions of other boards? 
See MACH_OMAP_H2 for example. The H2 depends on MACH_OMAP_INNOVATOR and expands 
it. This is done by an additional select MACH_OMAP_INNOVATOR in MACH_OMAP_H2
configuration option. With this the whole MACH_OMAP_INNOVATOR configuration is
selected and an additional symbol CONFIG_MACH_OMAP_H2 is available to
distinguish between INNOVATOR and H2 where necessary. 

3a. Only for new processors: Add the ARCH_OMAPxxxx to the correct ARM core in 
arch/arm/mm/Kconfig. E.g. ARCH_OMAP730 in CPU_ARM926T configuration.

3b. Only for new boards: Register the board within ARM Linux machine 
registration system from RMK. For the CONFIG_ section use the same name like 
in arch/arm/mach-omap[1/2]/Kconfig. E.g. MACH_OMAP_yyyy. For MACH_TYPE_ section use
OMAP_yyyy where yyyy is the board name like above.

Note: The elements of RMKs machine registration are used in 
arch/arm/tools/mach-types. While kernel compilation
include/asm-arm/mach-types.h is generated automagically from this file. The
content of mach-types.h then is used for machine identification by kernel
bootcode and can be used for board identification.

Note: The ARM Linux machine registration system from RMK can be found under:

www.arm.linux.org.uk/developer/machines/

Note: Only OMAP based boards should be registered to RMKs registration
system. Not processors.

4. Add a processor or board specific header file in include/asm-arm/arch-omap/. 
Use board-yyyy.h with yyyy board name or omapxxxx.h with xxxx processor number.

5. Add a processor or board specific section into include/asm-arm/arch-omap/
hardware.h. Use examples for syntax and use CONFIG_ names as defined in 
arch/arm/mach-omap[1/2]/Kconfig.

6. Add processor or board specific macros to board-yyyy.h or omapxxxx.h. The
macros to these specific files have to be named OMAPxxxx_ with xxxx processor
number to make them unique.

7a. Only for new boards: Add a file board-yyyy.c with yyyy board name to 
arch/arm/mach-omap[1/2]/. Put board specific initialization code and resource
description into this file. The first element of MACHINE_START must be equal to 
MACH_TYPE_ section of machine registration (see arch/arm/tools/mach-types after 
machine registration at RMKs registration system).

Put only code into this file that is board specific and not common. See other 
board files for examples.

7b. Only for new processors: Add processor specific IO description and
iotable_init() to arch/arm/mach-omap[1/2]/io.c. See examples for the syntax.

If you have introduced new clock definition in 2., add support for this new
clock in include/asm-arm/arch-omap/clocks.h and arch/arm/mach-omap[1/2]/clocks.c.

8. Only for new boards: Add "obj-$(CONFIG_MACH_OMAP_yyyy) += board-yyyy.o" with 
yyyy board name to arch/arm/mach-omap[1/2]/Makefile. This is used to compile your new
board specific initialization code from 7a.

9. Check if other of the existing files have to be adjusted for the new 
processor or board. Things to check:

- Pin multiplexing
- GPIO configuration
- Power Management
- Clocking
- Interrupt controller and interrupt configuration
- Additional board specific things (e.g. FPGAs)

If other existing files or device drivers have to be changed, use the following 
mechanism for processor specific things:

#ifdef CONFIG_ARCH_OMAPxxxx
 	if (cpu_is_omapxxxx()) {
 		/* Do the OMAPxxxx processor specific magic */
 	}
#endif

Note: cpu_is_omapxxxx() macro is defined in include/asm-arm/arch-omap/hardware.h
and uses OMAP_ID_REG for runtime processor identifcation.

For board differentiation use board macro from include/asm-arm/mach-types.h:

#ifdef CONFIG_MACH_OMAP_yyyy
 	if (machine_is_omap_yyyy()) {
 		/* Do the board specific magic */
 	}
#endif

Note: If technically possible and already implemented the OMAP Linux kernel
has support for a "one binary fits all" machanism. That is, the goal is to be
able to enable support for multiple OMAP processors and/or boards in Kconfig
system. Then it is decided by bootparameters and at runtime on which processor 
and/or board the kernel is actually running on. With this machanism it is 
possible to use the same kernel binary on different OMAP processors or boards 
without recompiling. This is achived by the cpu_is_omapxxxx() and
machine_is_omap_yyyy() macros.

On the other hand, for memory limited embedded systems it should be possible
to compile the kernel with support for only one processor/board combination.
For this a kernel binary is necessary which isn't bloated with code for all
other (unused) processors and boards. This is achived by using the preprocessor
CONFIG_ARCH_OMAPxxxx and CONFIG_MACH_OMAP_yyyy macros around the runtime
cpu_is_omapxxxx() and machine_is_omap_yyyy() selection.

At the moment, the price for this flexibility is a increased number of #ifdef's
throughout the code.

10. Configure the kernel by make menuconfig or make xconfig and select the new 
processor or board.

11. Compile the kernel by an appropriate cross compilation toolchain. Make this
until the code compiles error and warning free. The kernel should also be 
compiled with the various debug checking thingies enabled (e.g.
CONFIG_DEBUG_SPINLOCK,  CONFIG_DEBUG_PAGEALLOC etc.).

/* ToDo: Anything to say about toolchain? */

12. Download the kernel image to the board and test it until it works ;-)

It's not in the scope of this document how to do this (use a appropriate 
bootloader or JTAG download).

Note: The kernel initialization code expects some special values in the
registers R0, R1 and R2 of the ARM processor. These registers have to be
written by bootloader or debugger before starting the kernel. R0 has to be
zero, R1 has to contain the machine number from machine registration in
arch/arm/tools/mach-types. R2 points to the physical address of tagged list
in system RAM. For more information see Documentation/arm/Booting.

While testing a new processor or board configuration, it is recommended to 
enable low level debugging. This uses low level output functions to print kernel
messages on serial line before console is working. Enable it by 

Kernel hacking -> Kernel debugging -> Kernel low-level debugging functions

in kernel configuration system.

13. Check that no other processors or boards are broken by the new code. A first
test is to successful compile the other omap_xxx configurations from 
arch/arm/configs/. Do this by e.g.

cd linux
make omap_innovator_1510_defconfig
Compile the kernel

Even better: Enable support for several processors and boards in Kconfig
system and compile kernel successfully.

14. Only for new boards: Add a new default board configuration to 
arch/arm/configs. Use omap_yyyy_xxxx_defconfig with yyyy boardname and xxxx 
processornumber as filename.

15. If the new code works, compiles without warnings and seems to break no other
configurations, post a patch to linux-omap-open-source@list.ti.com.

With sending a patch to the community, it is reviewed, can be used and tested by
other users. It then can be included into the public OMAP kernel tree. 

16. Then adapt device drivers or write additional drivers for non-existing 
processor peripherals or board devices. Improve and maintain the code for your 
new processor or board.


4. General guidelines to write clean and OMAP Linux compatible code
-------------------------------------------------------------------

- For register access use the __REG8/16/32() macros. At the moment, see first
example in include/asm-arm/arch-omap/hardware.h.

Allegedly __REG() makes at least some versions of GCC emit tighter code
than the more direct wrappers. Presumably by making it easier to use certain 
addressing modes. 

Make sure that the registers names are clearly marked as being registers
(and not addresses of registers). This has to be done by adding a '_REG'
suffix. E.g.

#define OMAP_ID_REG  (__REG32(0xfffed400))
#define DPLL_CTL_REG (__REG16(0xfffecf00))

__raw_read[bwl] and __raw_write[bwl] are deprecated. They will converted to
__REG8/16/32() syntax, soon. Don't use anything else like own pointer
definitions or in[bwl]/out[bwl] etc., too.

- Make read-modify-write register access preemption save. Use spin_lock() and 
spin_unlock() where necessary. If an IRQ handler can access the registers, 
use spin_lock_irqsave(), too. 

- Functions declared as __init shouldn't have any references after the kernel 
initialization phase is complete. Usually they should be static as well.

- Don't use return statements at end of void functions.

- Use consistent indentation style. Don't use space indentations. Use tab 
indentations.

- In general use Linux formatting style. See Documentation/CodingStyle for more
information. If you use GNU emacs, see also chapter 8 of that document how to
add a linux-c-mode to emacs.


------------------------------------------------------------------
Last modified 15. March 2006
The OMAP Linux Kernel Team
Dirk Behme <dirk.behme@de.bosch.com>
