diff options
Diffstat (limited to 'arch/i386/cpu/start.S')
| -rw-r--r-- | arch/i386/cpu/start.S | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/arch/i386/cpu/start.S b/arch/i386/cpu/start.S index 1980f1a..3cea04b 100644 --- a/arch/i386/cpu/start.S +++ b/arch/i386/cpu/start.S @@ -33,7 +33,27 @@ .type _start, @function .globl _i386boot_start _i386boot_start: + /* + * This is the fail safe 32-bit bootstrap entry point. The + * following code is not executed from a cold-reset (actually, a + * lot of it is, but from real-mode after cold reset. It is + * repeated here to put the board into a state as close to cold + * reset as necessary) + */ + cli + cld + + /* Turn of cache (this might require a 486-class CPU) */ + movl %cr0, %eax + orl $0x60000000,%eax + movl %eax, %cr0 + wbinvd + + /* Tell 32-bit code it is being entered from an in-RAM copy */ + movw $0x0000, %bx _start: + /* This is the 32-bit cold-reset entry point */ + movl $0x18,%eax /* Load our segement registes, the * gdt have already been loaded by start16.S */ movw %ax,%fs @@ -42,6 +62,18 @@ _start: movw %ax,%es movw %ax,%ss + /* Clear the interupt vectors */ + lidt blank_idt_ptr + + /* + * Skip low-level board and memory initialization if not starting + * from cold-reset. This allows us to do a fail safe boot-strap + * into a new build of U-Boot from a known-good boot flash + */ + movw $0x0001, %ax + cmpw %ax, %bx + jne mem_init_ret + /* We call a few functions in the board support package * since we have no stack yet we'll have to use %ebp * to store the return address */ @@ -138,3 +170,7 @@ stack_ok: die: hlt jmp die hlt + +blank_idt_ptr: + .word 0 /* limit */ + .long 0 /* base */ |