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|
;; -----------------------------------------------------------------------
;;
;; Copyright 1994-2004 H. Peter Anvin - All Rights Reserved
;;
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, Inc., 53 Temple Place Ste 330,
;; Boston MA 02111-1307, USA; either version 2 of the License, or
;; (at your option) any later version; incorporated herein by reference.
;;
;; -----------------------------------------------------------------------
;;
;; highmem.inc
;;
;; Probe for the size of high memory. This can be overridden by a
;; mem= command on the command line while booting a new kernel.
;;
section .text
;
; This is set up as a subroutine; it will set up the global variable
; HighMemSize. All registers are preserved. Assumes DS == CS.
;
highmemsize:
push es
pushad
;
; First, try INT 15:E820 (get BIOS memory map)
;
get_e820:
xor ebx,ebx ; Start with first record
mov dword [E820Max],-(1 << 20) ; Max amount of high memory
mov dword [E820Mem],ebx ; Detected amount of high memory
mov es,bx ; Need ES = DS = 0 for now
jmp short .do_e820 ; Skip "at end" check first time!
.int_loop: and ebx,ebx ; If we're back at beginning...
jz .e820_done ; ... we're done
.do_e820: mov eax,0000E820h
mov edx,534D4150h ; "SMAP" backwards
xor ecx,ecx
mov cl,20 ; ECX <- 20
mov di,E820Buf
int 15h
jnc .no_carry
; If carry, ebx == 0 means error, ebx != 0 means we're done
and ebx,ebx
jnz .e820_done
jmp no_e820
.no_carry:
cmp eax,534D4150h
jne no_e820
;
; Look for a memory block starting at <= 1 MB and continuing upward
;
cmp dword [E820Buf+4], byte 0
ja .int_loop ; Start >= 4 GB?
mov edx, (1 << 20)
sub edx, [E820Buf]
jnb .ram_range ; Start >= 1 MB?
; If we get here, it starts > 1 MB but < 4 GB; if this is a
; *non*-memory range, remember this as unusable; some BIOSes
; get the length of primary RAM wrong!
cmp dword [E820Buf+16], byte 1
je .int_loop ; If it's memory, don't worry about it
neg edx ; This means what for memory limit?
cmp edx,[E820Max] ; Better or worse
jnb .int_loop
mov [E820Max],edx
jmp .int_loop
.ram_range:
stc
sbb eax,eax ; eax <- 0xFFFFFFFF
cmp dword [E820Buf+12], byte 0
ja .huge ; Size >= 4 GB
mov eax, [E820Buf+8]
.huge: sub eax, edx ; Adjust size to start at 1 MB
jbe .int_loop ; Completely below 1 MB?
; Now EAX contains the size of memory 1 MB...up
cmp dword [E820Buf+16], byte 1
jne .int_loop ; High memory isn't usable memory!!!!
; We're good!
mov [E820Mem],eax
jmp .int_loop ; Still need to add low 1 MB
.e820_done:
mov eax,[E820Mem]
and eax,eax
jz no_e820 ; Nothing found by E820?
cmp eax,[E820Max] ; Make sure we're not limited
jna got_highmem_add1mb
mov eax,[E820Max]
jmp got_highmem_add1mb
;
; INT 15:E820 failed. Try INT 15:E801.
;
no_e820:
mov ax,0e801h ; Query high memory (semi-recent)
int 15h
jc no_e801
cmp ax,3c00h
ja no_e801 ; > 3C00h something's wrong with this call
jb e801_hole ; If memory hole we can only use low part
mov ax,bx
shl eax,16 ; 64K chunks
add eax,(16 << 20) ; Add first 16M
jmp short got_highmem
;
; INT 15:E801 failed. Try INT 15:88.
;
no_e801:
mov ah,88h ; Query high memory (oldest)
int 15h
cmp ax,14*1024 ; Don't trust memory >15M
jna e801_hole
mov ax,14*1024
e801_hole:
and eax,0ffffh
shl eax,10 ; Convert from kilobytes
got_highmem_add1mb:
add eax,(1 << 20) ; First megabyte
got_highmem:
%if HIGHMEM_SLOP != 0
sub eax,HIGHMEM_SLOP
%endif
mov [HighMemSize],eax
popad
pop es
ret ; Done!
section .bss
alignb 4
E820Buf resd 5 ; INT 15:E820 data buffer
E820Mem resd 1 ; Memory detected by E820
E820Max resd 1 ; Is E820 memory capped?
HighMemSize resd 1 ; End of memory pointer (bytes)
|
