===========================
APEX Boot Loader
Release Notes & Quickstart
===========================
The APEX boot loader has been designed to be small, efficient, and
easy to extend. It uses some code and the build system from the Linux
kernel. There are pieces of code taken from BLOB and UBoot as well.
Newer Versions of APEX
----------------------
There is an ftp archive of APEX releases.
<ftp://ftp.buici.com/pub/apex>
There is also a wiki with information about APEX.
<http://wiki.buici.com/wiki/Apex_Bootloader>
Supported Targets
-----------------
The loader is fully functional for the LPD79524, LPD7A400, LPD7A404,
IXP42X. It builds for the LPD79520, but there is presently no version
of the Linux kernel that recognizes the correct architecture number.
APEX also builds for the MX31 and the S3C2410.
Building APEX
-------------
The config file has an option to define cross-compiler prefix. It
must be set unless you are building on an ARM host platform. For
example,
CROSS_COMPILE=/usr/arm-linux/gcc-3.4.1-glibc-2.3.3/bin/arm-linux-
The cross compiler may also be set in the environment or on the make
command line. Doing so will override the value set in the
configuration file.
make CROSS_COMPILE=/usr/arm-linux/gcc-3.4.1-glibc-2.3.3/bin/arm-linux-
Development proceeds with the 3.x compilers. GCC 2.95.3 does build
APEX at a slight penalty in code size.
Beware of GCC 2.95.3. It does not properly honor the naked function
-------------------- attribute which means that it may improperly
handle register allocation. The relocate_apex() function is
vulnerable to the problem and may cause APEX to fail. If you must use
GCC 2.95.3, make sure that there are no DEBUG_LL calls in
relocate_apex().
Like the Linux kernel, building APEX requires a configuration file
called '.config'. To build using the default configuration for the
LPD79524:
# make lpd79524_config
To change the default configuration, use one of the configuration
programs.
# make xconfig
APEX uses the Linux kernel build scripts so that rebuilding is as
optimal as the kernel. Changes to the configuration are automatically
propagated such that only affected source files are rebuilt.
# make
The ELF format binary, apex, as well as a link to the dumped apex.bin
will be put into the root directory.
Running APEX
------------
APEX is designed to start from any address and to relocate itself when
necessary. If the binary is small enough (less than 16KiB), it may be
copied to the internal SRAM of the LH79524 and executed from there.
Once you see the apex> prompt, the loader may be copied to flash and
the environment edited. Below is the signon message. It may be
reprinted with the 'version' command.
apex> ver
APEX Boot Loader 1.0.6 -- Copyright (c) 2004 Marc Singer
APEX comes with ABSOLUTELY NO WARRANTY. It is free software and you
are welcome to redistribute it under certain circumstances.
Refer to the source the COPYING for details.
apex => mem:0x20200000#0x4a94
env => nor:128k#64k
CPLD revision 0x5
The apex and env region specifications are important. The apex spec
describes where in RAM apex has been relocated as well as the exact
length of the program. The env spec describes where in flash the
environment is stored.
Assuming that APEX needs to be the first program in NOR flash, writing
APEX to flash looks like this.
apex> erase nor:0
apex> copy mem:0x20200000#0x4a94 nor:0
The source of the copy command is the descriptor from the signon
message. Preparing the environment area is even simpler.
apex> erase nor:128k#64k
Again, using the information in the signon to erase the proper portion
of flash. The environment allows APEX to be customized at runtime.
o Bootstraping APEX with LOLO or a JTAG emulator
o Downloading the kernel using XMODEM
o Changing the startup command to copy the kernel to RAM
o Changing the kernel command line
o Changing the startup command to automatically boot the kernel
Checksum Compatibility
----------------------
The checksum command built into APEX conforms to the POSIX.2 standard
algorithm which is also used by GNU cksum. This is not compatible
with the BSD sum command or with md5sum.
Getting Help
------------
Beyond what is here, you can send mail directly to me, the author.
Marc Singer <elf@buici.com>