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CWSDPMI is Copyright (C) 1995-2000 Charles W Sandmann (sandmann@clio.rice.edu)
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1206 Braelinn, Sugar Land, TX 77479
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This is release 5. The files in this binary distribution may be redistributed
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under the GPL (with source) or without the source code provided:
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* CWSDPMI.EXE or CWSDPR0.EXE are not modified in any way except via CWSPARAM.
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* CWSDSTUB.EXE internal contents are not modified in any way except via
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CWSPARAM or STUBEDIT. It may have a COFF image plus data appended to it.
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* Notice to users that they have the right to receive the source code and/or
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binary updates for CWSDPMI. Distributors should indicate a site for the
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source in their documentation.
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-------------------------------------------------------------------------------
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CWSDPMI was written to provide DPMI services for V2 of DJGPP. It currently
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does not support 16-bit DPMI applications, or DPMI applications requiring a
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built in extender. It does support virtual memory and hardware interrupt
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reflection from real mode to protected mode. DJGPP V1.1x and RSX applications
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will also run using this server, which can be used to provide enhanced control
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over hardware interrupts. Some DPMI 1.0 extensions (0x506, 0x507, 0x508) have
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CWSDPR0.EXE is an alternate version which runs at ring 0 with virtual memory
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disabled. It may be used if access to ring-0 features are desired. It
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currently does not switch stacks on HW interrupts, so some DJGPP features
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such as SIGINT and SIGFPE are not supported and will generate a double fault
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or stack fault error (to be fixed someday).
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CWSDSTUB.EXE is a stub loader image for DJGPP which includes CWSDPMI. This
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allows single executable image distributions. You can use the EXE2COFF
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program and COPY /B CWSDSTUB.EXE+yourimage yourimage.exe to create a
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standalone executable image.
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Some of the internal tuning and configuration parameters may be modified
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in the image using CWSPARAM.EXE (see CWSPARAM.DOC).
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If you want to use CWSDPMI with DJGPP, you expand the distribution into the
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DJGPP directory tree. CWSDPMI.EXE will be put in the BIN directory with your
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DJGPP images and it will automatically be loaded when they run.
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Directions for use (server can be used in either of two different ways):
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1) "cwsdpmi" alone with no parameters will terminate and stay resident
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FOR A SINGLE DPMI PROCESS. This means it unloads itself when your
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DPMI application exits. This mode is useful in software which needs
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DPMI services, since CWSDPMI can be exec'ed and then will unload on exit.
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2) "cwsdpmi -p" will terminate and stay resident until you remove it.
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It can be loaded into UMBs with LH. "cwsdpmi -u" will unload the TSR.
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3) The file used for virtual memory swapping, if desired, is controlled
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by the "-sc:\cwsdpmi.swp" syntax on the command line. You must specify
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either a file with full disk/directory syntax, or "-s-" which disables
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4) The default swap file name is c:\cwsdpmi.swp, but this can be changed
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with the CWSPARAM image, as can some other parameters.
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5) You can disable the DPMI 1.0 extensions by starting the image with the
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"cwsdpmi -x" syntax. This feature allows you to run programs developed
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under other DPMI providers which do not behave properly with these
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extensions enabled (typically use of NULL pointers).
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I would like to give special thanks to DJ Delorie who wrote the original
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GO32 code on which CWSDPMI is based. Morten Welinder also provided and
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improved much of the code in this program.
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-------------------------------------------------------------------------------
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This section contains a list of the error messages you might see out of
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CWSDPMI and some details on what they mean.
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Exceptions are only handled by CWSDPMI if the application does not establish
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an exception handler, exceptions nest 5 deep, or the error is particularly bad:
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1) an illegal page fault happens in a RMCB or HW interrupt, (lock all pages!)
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2) all available pages have been locked,
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3) the application is using non-committed pages for null pointer protection.
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"Double Fault" - multiple exceptions occurred
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"Invalid TSS" - typically due to RMCB or HW interrupt being called after the
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selectors/memory have been deallocated (remember to reset the mouse)
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"General Protection Fault" - bad parameter sent to a DPMI call
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Since 80286 and lesser processors don't have the hardware necessary to
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run CWSDPMI. No workaround, upgrade.
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A few interrupts are used which need DOS 3.0 or higher. I don't expect to
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ever see this message, since 80386 machines were introduced after DOS 3.0
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and that check is made first.
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"CWSDPMI V0.90+ (r5) Copyright (C) 2000 CW Sandmann ABSOLUTELY NO WARRANTY"
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An informational message displayed if the program is not run in one-pass mode.
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"Protected mode not accessible."
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This message should only be displayed if running CWSDPMI in a protected
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environment with no access to protected mode. In this case, DPMI should
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already be available and CWSDPMI would not be needed. This might happen if
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a 16-bit DPMI client is loaded and a DJGPP image attempts to load CWSDPMI
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to provide 32-bit DPMI services under Windows.
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"Warning: cannot open swap file c:\cwsdpmi.swp"
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Maybe you are out of file handles, or the swap file name is incorrectly
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specified in the image (change the name with cwsparam).
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This message means you tried to use more paging file than CWSDPMI was
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configured to handle. Since this is protected against in the memory
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allocation code, you should never see this message.
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This means the paging file could not be expanded when trying to page
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memory out to disk. This would normally not be seen, unless you are
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writing output to the same disk which holds the paging file. Decrease
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the amount of memory your DPMI application is using or free up disk space.
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Your application tried to call an interrupt from protected mode which
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normally shouldn't be called (something like a data pointer). If the
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request was allowed to continue it would likely hang your machine. If you
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see this message and think the interrupt should be allowed to continue, let
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"Error: Using XMS switched CPU into V86 mode."
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This message might be seen if you have your memory manager in AUTO mode. The
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only workaround in this case is to stop using AUTO mode.
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"Error: could not allocate page table memory"
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The page table memory (a minimum of 16Kb) is allocated from conventional
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memory (either in the 640Kb region or UMBs). If CWSDPMI cannot allocate the
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minimum necessary memory, you would see this message. Free up some
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conventional memory. You may also see this message if a page directory needs
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to be faulted in, and there are no available pages. This means too many pages
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have been locked for the allocated page tables available. While CWSDPMI
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tries to dynamically allocate these if needed, this effort failed. You need
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to increase the number of page tables with CWSPARAM, or increase the amount
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of free conventional memory if it is low. If the application which calls
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CWSDPMI internally manages all the DOS memory, the page tables may need to
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be pre-allocated at DPMI startup time (if this is needed, try using the
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run option flag 2 in cwsparam).
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"16-bit DPMI unsupported."
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CWSDPMI is a 32-bit only DPMI server. Ideally, on the request to enter DPMI's
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PM with a 16-bit request, we would just fail the call setting the carry bit
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like the DPMI specification describes. Some buggy 16-bit compiler tools don't
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check the return status and will hang the machine in this case. So, I issue
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an error message and exit the image instead.
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"Descriptors exhausted."
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An attempt to nest a DPMI client failed in the setup phase due to insufficient
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free selectors in the LDT.
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"CWSDPMI not removed"
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When the -u parameter is specified, if DPMI is not detected this message is
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printed. Informational.
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os/dos/cwsdpmi.txt
