x86: Add RAM bootstrap functionality
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>
diff --git a/arch/i386/cpu/start16.S b/arch/i386/cpu/start16.S
index 1ebb6bc..5e33aa1 100644
--- a/arch/i386/cpu/start16.S
+++ b/arch/i386/cpu/start16.S
@@ -45,10 +45,8 @@
wbinvd
/* load the descriptor tables */
-o32 cs lidt idt_ptr
o32 cs lgdt gdt_ptr
-
/* Now, we enter protected mode */
movl %cr0, %eax
orl $1,%eax
@@ -57,6 +55,8 @@
/* Flush the prefetch queue */
jmp ff
ff:
+ /* Tell 32-bit code it is being entered from hard-reset */
+ movw $0x0001, %bx
/* Finally jump to the 32bit initialization code */
movw $code32start, %ax
@@ -68,10 +68,6 @@
.long _start /* offset */
.word 0x10 /* segment */
-idt_ptr:
- .word 0 /* limit */
- .long 0 /* base */
-
gdt_ptr:
.word 0x30 /* limit (48 bytes = 6 GDT entries) */
.long BOOT_SEG + gdt /* base */