early_board_init has been skipped to avoid SDRAM corruption in the case
that a fully relocatable image has been loaded into SDRAM and is being
executed from SDRAM. x86 is being aligned with other architectures (ARM
and PPC in particlar) and will be using Cache-As-RAM to run a C
environment from Flash (or SRAM if you have some). early_board_init may
be needed to assist in the setup of Cache-As-RAM and the early C
environment
u-boot.bin can be loaded at any 4-byte aligned memory location and directly
'jumped' to using the 'go' command using the load address as the start
address. Doing so performs a 'warm boot' which skips memory initialisation
and other low-level initialisations, relocates U-Boot to upper memory and
starts U-Boot in RAM as per normal 'cold boot'
By reserving space for the Global Data immediately below the stack during
assembly level initialisation, the C declaration of the static global data
can be removed, along with the 'RAM Bootstrap' function. This results in
cleaner code, and the ability to pass boot-up flags from assembler into C
Change to:
- reparam=3
- no-from-pointer
- no-stack-protector
- preferred-stack-boundary=2
- no-top-level-reorder
These options make the code a little smaller and faster
Currently, the GDT is either located in FLASH or in the non-relocated
U-Boot image in RAM. Both of these locations are unsafe as those
locations can be erased during a U-Boot update. Move the GDT into the
highest available memory location and relocate U-Boot to just below it
Signed-off-by: Graeme Russ <graeme.russ@gmail.com>
Add a parameter to the 32-bit entry to indicate if entry is from Real
Mode or not. If entry is from Real Mode, execute the destructive 'sizer'
routine to determine memory size as we are booting cold and running in
Flash. If not entering from Real Mode, we are executing a U-Boot image
from RAM and therefore the memory size is already known (and running
'sizer' will destroy the running image)
There are now two 32-bit entry points. The first is the 'in RAM' entry
point which exists at the start of the U-Boot binary image. As such,
you can load u-boot.bin in RAM and jump directly to the load address
without needing to calculate any offsets. The second entry point is
used by the real-to-protected mode switch
This patch also changes TEXT_BASE to 0x6000000 (in RAM). You can load
the resulting image at 0x6000000 and simple go 0x6000000 from the u-boot
prompt
Hopefully a later patch will completely elliminate any dependency on
TEXT_BASE like a relocatable linux kernel (perfect world)
Signed-off-by: Graeme Russ <graeme.russ@gmail.com>
This patch allows the low-level assembler boot-strap to obtain the RAM
size without calling the destructive 'sizer' routine. This allows
boot-strapping from a U-Boot image loaded in RAM
Signed-off-by: Graeme Russ <graeme.russ@gmail.com>
Graeme Russ