README

Info data is placed, followed by the stack (growing downward).

Additionally, some exception handler code is copied to the low 8 kB
of DRAM (0x00000000 ... 0x00001FFF).

So a typical memory configuration with 16 MB of DRAM could look like
this:

	0x0000 0000	Exception Vector code
	      :
	0x0000 1FFF
	0x0000 2000	Free for Application Use
	      :
	      :

	      :
	      :
	0x00FB FF20	Monitor Stack (Growing downward)
	0x00FB FFAC	Board Info Data and permanent copy of global data
	0x00FC 0000	Malloc Arena
	      :
	0x00FD FFFF
	0x00FE 0000	RAM Copy of Monitor Code
	...		eventually: LCD or video framebuffer
	...		eventually: pRAM (Protected RAM - unchanged by reset)
	0x00FF FFFF	[End of RAM]


System Initialization:
----------------------

In the reset configuration, U-Boot starts at the reset entry point
(on most PowerPC systems at address 0x00000100). Because of the reset
configuration for CS0# this is a mirror of the onboard Flash memory.
To be able to re-map memory U-Boot then jumps to its link address.
To be able to implement the initialization code in C, a (small!)
initial stack is set up in the internal Dual Ported RAM (in case CPUs
which provide such a feature like MPC8xx or MPC8260), or in a locked
part of the data cache. After that, U-Boot initializes the CPU core,
the caches and the SIU.

Next, all (potentially) available memory banks are mapped using a
preliminary mapping. For example, we put them on 512 MB boundaries
(multiples of 0x20000000: SDRAM on 0x00000000 and 0x20000000, Flash
on 0x40000000 and 0x60000000, SRAM on 0x80000000). Then UPM A is
programmed for SDRAM access. Using the temporary configuration, a
simple memory test is run that determines the size of the SDRAM
banks.

When there is more than one SDRAM bank, and the banks are of
different size, the largest is mapped first. For equal size, the first
bank (CS2#) is mapped first. The first mapping is always for address
0x00000000, with any additional banks following immediately to create
contiguous memory starting from 0.

Then, the monitor installs itself at the upper end of the SDRAM area
and allocates memory for use by malloc() and for the global Board
Info data; also, the exception vector code is copied to the low RAM
pages, and the final stack is set up.

Only after this relocation will you have a "normal" C environment;
until that you are restricted in several ways, mostly because you are
running from ROM, and because the code will have to be relocated to a
new address in RAM.


U-Boot Porting Guide:
----------------------

[Based on messages by Jerry Van Baren in the U-Boot-Users mailing
list, October 2002]


int main(int argc, char *argv[])
{
	sighandler_t no_more_time;

	signal(SIGALRM, no_more_time);
	alarm(PROJECT_DEADLINE - toSec (3 * WEEK));

	if (available_money > available_manpower) {
		Pay consultant to port U-Boot;
		return 0;
	}

	Download latest U-Boot source;

	Subscribe to u-boot mailing list;

	if (clueless)
		email("Hi, I am new to U-Boot, how do I get started?");

	while (learning) {
		Read the README file in the top level directory;
		Read http://www.denx.de/twiki/bin/view/DULG/Manual;
		Read applicable doc/*.README;
		Read the source, Luke;
		/* find . -name "*.[chS]" | xargs grep -i <keyword> */
	}

	if (available_money > toLocalCurrency ($2500))
		Buy a BDI3000;
	else
		Add a lot of aggravation and time;

	if (a similar board exists) {	/* hopefully... */
		cp -a board/<similar> board/<myboard>
		cp include/configs/<similar>.h include/configs/<myboard>.h
	} else {
		Create your own board support subdirectory;
		Create your own board include/configs/<myboard>.h file;
	}
	Edit new board/<myboard> files
	Edit new include/configs/<myboard>.h

	while (!accepted) {
		while (!running) {
			do {
				Add / modify source code;
			} until (compiles);
			Debug;
			if (clueless)
				email("Hi, I am having problems...");
		}
		Send patch file to the U-Boot email list;
		if (reasonable critiques)
			Incorporate improvements from email list code review;
		else
			Defend code as written;
	}

	return 0;
}

void no_more_time (int sig)
{
      hire_a_guru();
}


Coding Standards:
-----------------

All contributions to U-Boot should conform to the Linux kernel
coding style; see the file "Documentation/CodingStyle" and the script
"scripts/Lindent" in your Linux kernel source directory.

Source files originating from a different project (for example the
MTD subsystem) are generally exempt from these guidelines and are not
reformated to ease subsequent migration to newer versions of those
sources.

Please note that U-Boot is implemented in C (and to some small parts in
Assembler); no C++ is used, so please do not use C++ style comments (//)
in your code.

Please also stick to the following formatting rules:
- remove any trailing white space
- use TAB characters for indentation and vertical alignment, not spaces
- make sure NOT to use DOS '\r\n' line feeds
- do not add more than 2 consecutive empty lines to source files
- do not add trailing empty lines to source files

Submissions which do not conform to the standards may be returned
with a request to reformat the changes.


Submitting Patches:
-------------------

Since the number of patches for U-Boot is growing, we need to
establish some rules. Submissions which do not conform to these rules
may be rejected, even when they contain important and valuable stuff.

Please see http://www.denx.de/wiki/U-Boot/Patches for details.

Patches shall be sent to the u-boot mailing list <u-boot@lists.denx.de>;
see http://lists.denx.de/mailman/listinfo/u-boot

When you send a patch, please include the following information with
it:

* For bug fixes: a description of the bug and how your patch fixes
  this bug. Please try to include a way of demonstrating that the
  patch actually fixes something.

* For new features: a description of the feature and your
  implementation.

* A CHANGELOG entry as plaintext (separate from the patch)

* For major contributions, your entry to the CREDITS file

* When you add support for a new board, don't forget to add this
  board to the MAINTAINERS file, too.

* If your patch adds new configuration options, don't forget to
  document these in the README file.

* The patch itself. If you are using git (which is *strongly*
  recommended) you can easily generate the patch using the
  "git format-patch". If you then use "git send-email" to send it to
  the U-Boot mailing list, you will avoid most of the common problems
  with some other mail clients.

  If you cannot use git, use "diff -purN OLD NEW". If your version of
  diff does not support these options, then get the latest version of
  GNU diff.

  The current directory when running this command shall be the parent
  directory of the U-Boot source tree (i. e. please make sure that
  your patch includes sufficient directory information for the
  affected files).

  We prefer patches as plain text. MIME attachments are discouraged,
  and compressed attachments must not be used.

* If one logical set of modifications affects or creates several
  files, all these changes shall be submitted in a SINGLE patch file.

* Changesets that contain different, unrelated modifications shall be
  submitted as SEPARATE patches, one patch per changeset.


Notes:

* Before sending the patch, run the MAKEALL script on your patched
  source tree and make sure that no errors or warnings are reported
  for any of the boards.

* Keep your modifications to the necessary minimum: A patch
  containing several unrelated changes or arbitrary reformats will be
  returned with a request to re-formatting / split it.

* If you modify existing code, make sure that your new code does not
  add to the memory footprint of the code ;-) Small is beautiful!
  When adding new features, these should compile conditionally only
  (using #ifdef), and the resulting code with the new feature
  disabled must not need more memory than the old code without your
  modification.

* Remember that there is a size limit of 100 kB per message on the
  u-boot mailing list. Bigger patches will be moderated. If they are
  reasonable and not too big, they will be acknowledged. But patches
  bigger than the size limit should be avoided.