config.gml

开放源码的编译器open watcom 1.6.0版的源代码

set DOS16M= [switch_mode] [@start_address [- end_address]] [:size]
.code end
.pc
In the syntax shown above,
.mono start_address,
.mono end_address
and
.mono size
represent numbers, expressed in decimal or in hexadecimal (hex
requires a
.mono 0x
prefix).
The number may end with a K to indicate an address or size in
kilobytes, or an M to indicate megabytes.
If no suffix is given, the address or size is assumed to be in
kilobytes.
If both a size and a range are specified, the more restrictive
interpretation is used.
.np
The most flexible strategy is to specify only a size.
However, if you are running with other software that does not follow a
convention for indicating its use of extended memory, and these other
programs start before &dos4g, you will need to calculate the range of
memory used by the other programs and specify a range for &dos4g
programs to use.
.np
&dos4g ignores specifications (or parts of specifications) that
conflict with other information about extended memory use.
Below are some examples of memory usage control:
.begnote $setptnt 24
.note set DOS16M= 1 @2m-4m
Mode 1, for NEC 98-series machines, and use extended memory between
2.0 and 4.0MB.
.note set DOS16M= :1M
Use the last full megabyte of extended memory, or as much as available
limited to 1MB.
.note set DOS16M= @2m
Use any extended memory available above 2MB.
.note set DOS16M= @ 0 - 5m
Use any available extended memory from 0.0 (really 1.0) to 5.0MB.
.note set DOS16M= :0
Use no extended memory.
.endnote
.np
As a default condition &dos4g applications take all extended memory
that is not otherwise in use.
Multiple &dos4g programs that execute simultaneously will share the
reserved range of extended memory.
Any non-&dos4gct programs started while &dos4g programs are executing
will find that extended memory above the start of the &dos4g range is
unavailable, so they may not be able to run.
This is very safe.
There will be a conflict only if the other program does not check the
BIOS configuration call (Interrupt 15H function 88H, get extended
memory size).
.np
.ix 'PRIVATXM'
To create a private pool of extended memory for your &dos4g
application, use the PRIVATXM program, described in the
chapter entitled :HDREF refid='rsiutls'..
.np
The default memory allocation strategy is to use extended memory if
available, and overflow into DOS (low) memory.
:cmt. :I1.D16MemStrategy
:cmt. If you require that your memory allocations be confined to your
:cmt. specified extended memory range, use the &dos4g function
:cmt. .mono D16MemStrategy(MForceExt)
:cmt. in your program.
.np
.ix 'VCPI'
.ix 'DPMI'
In a VCPI or DPMI environment, the
.mono start_address
and
.mono end_address
arguments are not meaningful.
&dos4g memory under these protocols is not allocated according to
specific addresses because VCPI and DPMI automatically prevent address
conflicts between extended memory programs.
You can specify a
.mono size
for memory managed by VCPI or DPMI, but &dos4g will not necessarily
allocate this memory from the highest available extended memory
address, as it does for memory managed under other protocols.
.*
.section Using Extra Memory
.*
.np
.ix '&dos4gprd' 'extra memory'
Some machines contain extra non-extended, non-conventional memory just
below 16MB.
.ix 'Compaq 386 memory'
When &dos4g runs on a Compaq 386, it automatically uses this memory
because the memory is allocated according to a certain protocol, which
&dos4g follows.
Other machines have no protocol for allocating this memory.
.ix 'DOS16M' '+ option'
To use the extra memory that may exist on these machines, set
.ev DOS16M
with the + option.
.millust begin
set DOS16M=+
.millust end
.np
Setting the + option causes &dos4g to search for memory in the range
from FA0000 to FFFFFF and determine whether the memory is usable.
&dos4g does this by writing into the extra memory and reading what it
has written.
In some cases, this memory is mapped for DOS or BIOS usage, or for
other system uses.
If &dos4g finds extra memory that is mapped this way, and is not
marked read-only, it will write into that memory.
This will cause a crash, but won't have any other effect on your
system.
.*
.endlevel
.*
.section Setting Runtime Options
.*
.np
.ix '&dos4gprd' 'runtime options'
.ix 'DOS16M' 'runtime options'
The
.ev DOS16M
environment variable sets certain runtime options for all &dos4g
programs running on the same system.
.np
To set the environment variable, the syntax is:
.millust begin
set DOS16M=[switch_mode_setting]^options.
.millust end
.np
.bd Note:
Some command line editing TSRs, such as CED, use the caret (^)
as a delimiter.
If you want to set
.ev DOS16M
using the syntax above while one of these TSRs is resident, modify the
TSR to use a different delimiter.
.np
These are the options:
.begnote
.note 0x01
.us check A20 line --
.ix 'A20 line'
.ix 'protected mode'
This option forces &dos4g to wait until the A20 line is enabled before
switching to protected mode.
.ix 'XMS'
.ix 'HIMEM.SYS'
.ix 'real mode'
When &dos4g switches to real mode, this option suspends your program's
execution until the A20 line is disabled, unless an XMS manager (such
as HIMEM.SYS) is active.
If an XMS manager is running, your program's execution is suspended
until the A20 line is restored to the state it had when the CPU was
last in real mode.
Specify this option if you have a machine that runs &dos4g but is not
truly AT-compatible.
For more information on the A20 line, see the
section entitled :HDREF refid='ctrl20'..
.note 0x02
.us prevent initialization of VCPI --
By default, &dos4g searches for a VCPI server and, if one is present,
forces it on.
This option is useful if your application does not use EMS explicitly,
is not a resident program, and may be used with 386-based EMS
simulator software.
.note 0x04
.us directly pass down keyboard status calls --
.ix 'keyboard status'
When this option is set, status requests are passed down immediately
and unconditionally.
.ix '8042 auxiliary processor'
When disabled, pass-downs are limited so the 8042 auxiliary processor
does not become overloaded by keyboard polling loops.
.note 0x10
.us restore only changed interrupts --
Normally, when a &dos4g program terminates, all interrupts are
restored to the values they had at the time of program startup.
When you use this option, only the interrupts changed by the &dos4g
program are restored.
.note 0x20
.us set new memory to 00 --
When &dos4g allocates a new segment or increases the size of a
segment, the memory is zeroed.
This can help you find bugs having to do with uninitialized memory.
You can also use it to provide a consistent working environment
regardless of what programs were run earlier.
This option only affects segment allocations or expansions that are
made through the &dos4g kernel (with DOS function 48H or 4AH).
This option does not affect memory allocated with a compiler's
.mono malloc
function.
.note 0x40
.us set new memory to FF --
When &dos4g allocates a new segment or increases the size of a
segment, the memory is set to 0xFF bytes.
This is helpful in making reproducible cases of bugs caused by using
uninitialized memory.
This option only affects segment allocations or expansions that are
made through the &dos4g kernel (with DOS function 48H or 4AH).
This option does not affect memory allocated with a compiler's
.mono malloc
function.
.note 0x80
.us new selector rotation --
When &dos4g allocates a new selector, it usually looks for the first
available (unused) selector in numerical order starting with the
highest selector used when the program was loaded.
When this option is set, the new selector search begins after the last
selector that was allocated.
This causes new selectors to rotate through the range.
Use this option to find references to
.us stale
selectors, i.e., segments that have been cancelled or freed.
.endnote
.*
.section *refid=ctrl20 Controlling Address Line 20
.*
.np
.ix '&dos4gprd' 'address line 20'
.ix 'address line 20'
.ix 'A20 line'
This section explains how &dos4g uses address line 20 (A20) and
describes the related
.ev DOS16M
environment variable settings.
It is unlikely that you will need to use these settings.
.np
Because the 8086 and 8088 chips have 20-bit address spaces, their
highest addressable memory location is one byte below 1MB.
If you specify an address at 1MB or over, which would require a
twenty-first bit to set, the address wraps back to zero.
Some parts of DOS depend on this wrap, so on the 286 and 386, the
twenty-first address bit is disabled.
To address extended memory, &dos4g enables the twenty-first address
bit (the A20 line).
The A20 line must be enabled for the CPU to run in protected mode, but
it may be either enabled or disabled in real mode.
.np
By default, when &dos4g returns to real mode, it disables the A20
line.
Some software depends on the line being enabled.
&dos4g recognizes the most common software in this class, the XMS
managers (such as HIMEM.SYS), and enables the A20 line when it returns
to real mode if an XMS manager is present.
.ix 'DOS16M' 'A20 option'
For other software that requires the A20 line to be enabled, use the
.mono A20
option.
The
.mono A20
option makes &dos4g restore the A20 line to the setting it had when
&dos4g switched to protected mode.
Set the environment variable as follows:
.millust begin
set DOS16M=A20
.millust end
.np
To specify more than one option on the command line, separate the
options with spaces.
.np
The
.ev DOS16M
variable also lets you to specify the length of the delay between a
&dos4g instruction to change the status of the A20 line and the next
&dos4g operation.
By default, this delay is 1 loop instruction when &dos4g is running on
a 386 machine.
In some cases, you may need to specify a longer delay for a machine
that will run &dos4g but is not truly AT-compatible.
To change the delay, set
.ev DOS16M
to the desired number of loop instructions, preceded by a comma:
.ix 'DOS16M' 'loops option'
.millust begin
set DOS16M=,loops
.millust end