MBOOT bootloader
================
MBOOT is a clone of well known das U-Boot, with reduced functionality. I think,
it is it's main benefit. The key point is:
Allow the board owner to write a code he needs to boot the board.
This means that there is no single board_init_r function for everyone with tones
of defines, callbacks, switches and bugs people are afraid to fix because they
think it can hurt someone else. Sorry for my English, there are probably some
grammar mistakes.
Other features:
* All board's boot procedure is in single file (actually, only one board is
supported - the one I have access to). See board/uemd/uemd.c for an
illustration.
* Smaller and cleaner Makefile. No symlinks, almost no generated files, still
supporting linux-style CONFIG_ defines. Works faster!
* Cleaner code: Network stack and Main loop now have explicit states, main
booting procedure is in single board-specific file, lighter environment system.
* New MTD stack and read-write routines.
* Easy framework for in-place generating of Linux tags and commad line.
* Relocation is no more, easy to debug.
Working commands are: help, setenv, getenv, saveenv, reset, bootm, mtdboot,
tftpboot, ping, version, mtd, fwupgrade and some other which are not so important.
Unfortunately, there are heavy limitations, U-boot is a huge project after all.
* Only Linux kernels, only legacy uImage format, no compression, no RAM disks
(but it can be added easily)
* One arch (ARM 1176), one board (unknown for the public).
* Simple serial console
COMPILE
=======
To build the bootloader one have to type
export CROSS_COMPILE=<your compiler prefix>
make -f Makefile.<board>
Known to work with my compiler - gcc version 4.4.5 p1.3, pie-0.4.5 built with
the help of Gentoo crossdev suit.
Extending
=========
Porting a new board
-------------------
Board-specific code::
Use board/uemd/ as an example. Create board/yourboard/ and write board-specific
code. Typically, you will need to write board entry-code (yourboard.S), main
routine (yourboard_main.c), and a linker script. Create separate header for
CONFIG_ macros. Insert following code (or somthing like that) to start
interaction with a user.
struct main_state ms;
main_state_init(&ms);
while(! MAIN_STATE_HAS_ENTRY(&ms)) {
ret = main_process_command(&ms);
if(ret != 0) {
board_hang();
}
}
To terminate the loop, some command should set ms.os_image to correct values.
The handler of bootm command does it for you. See uemd.c to find out how to
master linux command line and boot it.
Besides that, you have to define several board_ functions to make old-style code
work.
Console::
Copy board/uemd/uemd_console.c (simple serial console) to your board's
directory.
Makefile::
Write Makefile.yourboard (again, use Makefile.uemd as an example). Setup
BOARD_ variables, include arch/arm/ and arch/arm/cpu/ Makefiles. Finally,
include rules.mk and define 'all' and 'clean' rules. Refer to 'rules_all' and
'rules_clean' from rules.mk.
KNOWN BUGS
==========
* Makefile doesn't like when you remove headers.
* Tones of old U-boot code. Most of commands are disabled and have to be
adopted to the new format. See command.h for details.
* Nasty bug is lurking somewhere in readline function. Sometimes It stops working
when I press Ctrl+C.
--
Best regards,
Sergey Mironov
ierton@gmail.com
https://github.com/ierton/mboot