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okuji 1999-05-21 01:35:53 +00:00
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@ -979,7 +979,11 @@ where to find Stage 2, and the Stage 2 has to know where to find its
configuration file (if Stage 2 doesn't have a configuration file, it
drops into the command-line interface and waits for a user command).
Here is the memory map of the various components:
Here is the memory map of the various components
@footnote{Currently GRUB does not use the extended memory for itself,
since it is used to load an operating system. But we are planning to use
it for GRUB itself in the future by @dfn{lazy loading}. Ask okuji for
more information.}:
@table @asis
@item 0 to 4K-1
@ -1141,19 +1145,346 @@ which address range should be treated by operating systems.
@node Query System Address Map
@subsection INT 15H, AX=E820h interrupt call
mem64mb.html
Real mode only.
This call returns a memory map of all the installed @sc{ram}, and of
physical memory ranges reserved by the BIOS. The address map is returned
by making successive calls to this API, each returning one "run" of
physical address information. Each run has a type which dictates how
this run of physical address range should be treated by the operating
system.
If the information returned from INT 15h, AX=E820h in some way differs
from INT 15h, AX=E801h (@pxref{Get Large Memory Size}) or INT 15h AH=88h
(@pxref{Get Extended Memory Size}), then the information returned from
E820h supersedes what is returned from these older interfaces. This
allows the BIOS to return whatever information it wishes to for
compatibility reasons.
Input:
@multitable @columnfractions .15 .25 .6
@item @code{EAX} @tab Function Code @tab E820h
@item @code{EBX} @tab Continuation @tab Contains the @dfn{continuation
value} to get the next run of physical memory. This is the value
returned by a previous call to this routine. If this is the first call,
@code{EBX} must contain zero.
@item @code{ES:DI} @tab Buffer Pointer @tab Pointer to an Address Range
Descriptor structure which the BIOS is to fill in.
@item @code{ECX} @tab Buffer Size @tab The length in bytes of the
structure passed to the BIOS. The BIOS will fill in at most @code{ECX}
bytes of the structure or however much of the structure the BIOS
implements. The minimum size which must be supported by both the BIOS
and the caller is 20 bytes. Future implementations may extend this
structure.
@item @code{EDX} @tab Signature @tab @samp{SMAP} - Used by the BIOS to
verify the caller is requesting the system map information to be
returned in @code{ES:DI}.
@end multitable
Output:
@multitable @columnfractions 0.15 0.25 0.6
@item @code{CF} @tab Carry Flag @tab Non-Carry - indicates no error
@item @code{EAX} @tab Signature @tab @samp{SMAP} - Signature to verify
correct BIOS revision.
@item @code{ES:DI} @tab Buffer Pointer @tab Returned Address Range
Descriptor pointer. Same value as on input.
@item @code{ECX} @tab Buffer Size @tab Number of bytes returned by the
BIOS in the address range descriptor. The minimum size structure
returned by the BIOS is 20 bytes.
@item @code{EBX} @tab Continuation @tab Contains the continuation value
to get the next address descriptor. The actual significance of the
continuation value is up to the discretion of the BIOS. The caller must
pass the continuation value unchanged as input to the next iteration of
the E820h call in order to get the next Address Range Descriptor. A
return value of zero means that this is the last descriptor. Note that
the BIOS indicate that the last valid descriptor has been returned by
either returning a zero as the continuaition value, or by returning
carry.
@end multitable
The Address Range Descriptor Structure is:
@multitable @columnfractions 0.25 0.3 0.45
@item Offset in Bytes @tab Name @tab Description
@item 0 @tab @dfn{BaseAddrLow} @tab Low 32 Bits of Base Address
@item 4 @tab @dfn{BaseAddrHigh} @tab High 32 Bits of Base Address
@item 8 @tab @dfn{LengthLow} @tab Low 32 Bits of Length in Bytes
@item 12 @tab @dfn{LengthHigh} @tab High 32 Bits of Length in Bytes
@item 16 @tab @dfn{Type} @tab Address type of this range
@end multitable
The @dfn{BaseAddrLow} and @dfn{BaseAddrHigh} together are the 64 bit
@dfn{BaseAddress} of this range. The @dfn{BaseAddress} is the physical
address of the start of the range being specified.
The @dfn{LengthLow} and @dfn{LengthHigh} together are the 64 bit
@dfn{Length} of this range. The @dfn{Length} is the physical contiguous
length in bytes of a range being specified.
The @dfn{Type} field describes the usage of the described address range
as defined in the table below:
@multitable @columnfractions 0.1 0.35 0.55
@item Value @tab Pneumonic @tab Description
@item 1 @tab @dfn{AddressRangeMemory} @tab This run is available
@sc{ram} usable by the operating system.
@item 2 @tab @dfn{AddressRangeReserved} @tab This run of addresses is in
use or reserved by the system, and must not be used by the operating
system.
@item Other @tab @dfn{Undefined} @tab Undefined - Reserved for future
use. Any range of this type must be treated by the OS as if the type
returned was @dfn{AddressRangeReserved}.
@end multitable
The BIOS can use the @dfn{AddressRangeReserved} address range type to
block out various addresses as @emph{not suitable} for use by a
programmable device.
Some of the reasons a BIOS would do this are:
@itemize @bullet
@item
The address range contains system @sc{rom}.
@item
The address range contains @sc{ram} in use by the @sc{rom}.
@item
The address range is in use by a memory mapped system device.
@item
The address range is for whatever reason are unsuitable for a
standard device to use as a device memory space.
@end itemize
Here is the list of assumptions and limitations:
@enumerate
@item
The BIOS will return address ranges describing base board memory and ISA
or PCI memory that is contiguous with that base board memory.
@item
The BIOS @emph{will not} return a range description for the memory
mapping of PCI devices. ISA Option @sc{rom}'s, and ISA plug & play
cards. This is because the OS has mechanisms available to detect them.
@item
The BIOS will return chipset defined address holes that are not being
used by devices as reserved.
@item
Address ranges defined for base board memory mapped I/O devices (for
example APICs) will be returned as reserved.
@item
All occurrences of the system BIOS will be mapped as reserved. This
includes the area below 1 MB, at 16 MB (if present) and at end of the
address space (4 GB).
@item
Standard PC address ranges will not be reported. Example video memory at
A0000 to BFFFF physical will not be described by this function. THe
range from E0000 to EFFFF is base board specific and will be reported as
suits the bas board.
@item
All of lower memory is reported as normal memory. It is OS's
responsibility to handle standard @sc{ram} locations reserved for
specific uses, for example: the interrupt vector table (0:0) and the
BIOS data area (40:0).
@end enumerate
Here we explain an example address map. This sample address map
describes a machine which has 128 MB @sc{ram}, 640K of base memory and
127 MB extended. The base memory has 639K available for the user and 1K
for an extended BIOS data area. There is a 4 MB Linear Frame Buffer
(LFB) based at 12 MB. The memory hole created by the chipset is from 8
M to 16 M. There are memory mapped APIC devices in the system. The IO
Unit is at FEC00000 and the Local Unit is at FEE00000. The system BIOS
is remapped to 4G - 64K.
Note that the 639K endpoint of the first memory range is also the base
memory size reported in the BIOS data segment at 40:13.
Key to types: @dfn{ARM} is AddressRangeMemory, @dfn{ARR} is
AddressRangeReserved.
@multitable @columnfractions 0.15 0.1 0.1 0.65
@item Base (Hex) @tab Length @tab Type @tab Description
@item 0000 0000 @tab 639K @tab ARM @tab Available Base memory -
typically the same value as is returned via the INT 12 function.
@item 0009 FC00 @tab 1K @tab ARR @tab Memory reserved for use by the
BIOS(s). This area typically includes the Extended BIOS data area.
@item 000F 0000 @tab 64K @tab ARR @tab System BIOS.
@item 0010 0000 @tab 7M @tab ARM @tab Extended memory, this is not
limited to the 64MB address range.
@item 0080 0000 @tab 8M @tab ARR @tab Chipset memory hole required to
support the LFB mapping at 12 MB.
@item 0100 0000 @tab 120M @tab ARM @tab Base board @sc{ram} relocated
above a chipset memory hole.
@item FE00 0000 @tab 4K @tab ARR @tab IO APIC memory mapped I/O at
FEC00000. Note the range of addresses required for an APIC device may
vary from base OEM to OEM.
@item FEE0 0000 @tab 4K @tab ARR @tab Local APIC memory mapped I/O at
FEE00000.
@item FFFF 0000 @tab 64K @tab ARR @tab Remapped System BIOS at end of
address space.
@end multitable
The following code segment is intended to describe the algorithm needed
when calling the Query System Address Map function. It is an
implementation example and uses non standard mechanisms.
@example
E820Present = FALSE;
Regs.ebx = 0;
do
@{
Regs.eax = 0xE820;
Regs.es = SEGMENT (&Descriptor);
Regs.di = OFFSET (&Descriptor);
Regs.ecx = sizeof (Descriptor);
Regs.edx = 'SMAP';
_int (0x15, Regs);
if ((Regs.eflags & EFLAGS_CARRY) || Regs.eax != 'SMAP')
@{
break;
@}
if (Regs.ecx < 20 || Regs.ecx > sizeof (Descriptor))
@{
/* bug in bios - all returned descriptors must be at
least 20 bytes long, and can not be larger than
the input buffer. */
break;
@}
E820Present = TRUE;
.
.
.
Add address range Descriptor.BaseAddress through
Descriptor.BaseAddress + Descriptor.Length
as type Descriptor.Type
.
.
.
@}
while (Regs.ebx != 0);
if (! E820Present)
@{
.
.
.
call INT 15H, AX E801h and/or INT 15H, AH=88h to obtain old style
memory information
.
.
.
@}
@end example
@node Get Large Memory Size
@subsection INT 15H, AX=E801h interrupt call
mem64mb.html
Real mode only.
Originally defined for EISA servers, this interface is capable of
reporting up to 4 GB of @sc{ram}. While not nearly as flexible as
E820h, it is present in many more systems.
Input:
@multitable @columnfractions 0.15 0.25 0.6
@item @code{AX} @tab Function Code @tab E801h
@end multitable
Output:
@multitable @columnfractions 0.15 0.25 0.6
@item @code{CF} @tab Carry Flag @tab Non-Carry - indicates no error.
@item @code{AX} @tab Extended 1 @tab Number of contiguous KB between 1
and 16 MB, maximum 0x3C00 = 15 MB.
@item @code{BX} @tab Extended 2 @tab Number of contiguous 64KB blocks
between 16 MB and 4GB.
@item @code{CX} @tab Configured 1 @tab Number of contiguous KB between 1
and 16 MB, maximum 0x3c00 = 15 MB.
@item @code{DX} @tab Configured 2 @tab Number of contiguous 64KB blocks
between 16 MB and 4 GB.
@end multitable
Not sure what this difference between the @dfn{Extended} and
@dfn{Configured} numbers are, but they appear to be identical, as
reported from the BIOS.
It is possible for a machine using this interface to report a memory
hole just under 16 MB (Count 1 is less than 15 MB, but Count 2 is
non-zero).
@node Get Extended Memory Size
@subsection INT 15H, AX=88h interrupt call
mem64mb.html
Real mode only.
This interface is quite primitive. It returns a single value for
contiguous memory above 1 MB. The biggest limitation is that the value
returned is a 16-bit value, in KB, so it has a maximum saturation of
just under 64 MB even presuming it returns as much as it can. On some
systems, it won't return anything above the 16 MB boundary.
The one useful point is that it works on every PC available.
Input:
@multitable @columnfractions 0.15 0.25 0.6
@item @code{AH} @tab Function Code @tab 88h
@end multitable
Output:
@multitable @columnfractions 0.15 0.25 0.6
@item @code{CF} @tab Carry Flag @tab Non-Carry - indicates no error.
@item @code{AX} @tab Memory Count @tab Number of contiguous KB above 1
MB.
@end multitable
@node Low-level disk I/O