ARM based CPU (MACH) into the tree

FIXME

What's happens when the reset signal is gone

Note:

Code running immediately after reset runs at an address it is not linked to: "runtime address != link address". You should only use branches and do not refer to fixed data. This implies the use of assembler code only.

The ARM CPU starts at lable <reset> in one of the corresponding start-*.S files. After some basic hardware setup it can call a function <arch_init_lowlevel> if not disabled. This call is intended to give all developers a chance to use a standard reset vector file, but also do some special things required only on their specific CPU.

After handling some MMU related things <board_init_lowlevel> can be called (if not disabled). This is a board specific function for SDRAM setup for example. As its board specific, your can do whatever you need to bring your board up.

In the case the boot happens from NAND flash memory, further steps are required. Most of the known processor devices are reading the first few blocks from the NAND flash memory into some kind of internal SRAM. This small part must be able to initialize the SDRAM controller and to read the remaining rest of the barebox binary from the NAND flash memory prior returning from <board_init_lowlevel>.

When <board_init_lowlevel> returns it will be assumed there is now a working RAM that can be used for all further steps.

Next step is relocation of barebox itself (if not already done). It gets copied to RAM and the last assembler instruction is a jump into start_barebox(). This target address is the first C instruction in barebox. At this point of time:
"runtime address == link address".

List of changes

Lets call the new MACH new_cpu.

• create a new subdirectory in /arch/arm/new_cpu
• create a new subdirectory in /include/asm-arm/new_cpu
• add CPU specific definitions into /include/asm-arm/new_cpu/
• add /arch/arm/new_cpu/Kconfig
• add /arch/arm/new_cpu/Makfile
• add other CPU specific code into /arch/arm/new_cpu/
• modify /arch/arm/Kconfig
• modify /arch/arm/Makfile

Architectures using ARM processors

For details on specific architectures:

OMAP CPUs

• Texas Instrument's OMAP Platforms in barebox

S3C24XX CPUs

• Samsung's S3C24xx Platforms in barebox

TODO add more details