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CWSPARAM provided by Charles W Sandmann (sandmann@clio.rice.edu)
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1206 Braelinn, Sugar Land, TX 77479
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There are certain parameters built into the CWSDPMI.EXE, CWSDPR0.EXE, and
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CWSDSTUB.EXE images which might need to be modified for distributing some
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programs for better performance. The modified image could be renamed, and
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then the DPMI server name in a DJGPP V2 image may be stubedited to use the
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new name. CWSPARAM can also be run directly on images created by appending
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COFF images to CWSDSTUB.EXE. The parameters which can be modified are
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Full name of paging file ("" to disable) ? [c:\cwsdpmi.swp]
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This is where the file which provides virtual memory should be located. It
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may be desirable to change the default to a faster disk or one with more
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free space. To disable paging, enter two double quotes. The file name
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MUST contain the disk, full path, and file name. Anything less may cause
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unpredictable behavior. The maximum length of the name is 48 characters,
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and it must be a DOS 8.3 style name. Press return to keep the current value.
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Number of page tables to initially allocate (0=auto) ? [0]
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Page tables are stored in the DOS memory area and consume this precious
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resource. The default value of 0 chooses automatic allocation of enough
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page tables to hold all of the physical memory without paging (with the
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minimum enough to hold 20Mb without paging and a maximum to hold 128Mb).
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If your program is a fixed size (and does not spawn any other DPMI images)
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you can specify one page table for each 4Mb of your program's size. If
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your program is small, this can save a small amount of DOS memory, which
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might be needed for other purposes. If your program is large (typically
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larger than the physical memory) specifying a number will consume more DOS
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memory but improve performance since the page tables themselves will not
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page. CWSDPMI will attempt to dynamically allocate additional page tables
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at run time to prevent paging, but if all of the DOS memory is free,
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performance would be degraded. Remember to add an extra page table if
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mapping physical devices. As of r5, you must also allocate additional
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space for the bitmaps for physical and virtual memory (one bit for each
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4K page). Add one page for each 128Mb of total address space
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(physical+virtual). Be generous, since someone may run the image on a
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512Mb machine (or larger) and require 4 pages for the physical bitmap
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even if you disable virtual memory.
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Minimum application memory desired before 640K paging ? [512Kb]
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Typically, CWSDPMI only uses extended memory to return as DPMI memory, and
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saves the DOS memory area for DOS requests. On small memory machines with
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applications not needing much DOS memory (or poorly tuned memory management)
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there may be very little extended memory left available, with up to 600K of
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DOS memory unused. This parameter determines the threshold which CWSDPMI
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should start using DOS memory as DPMI memory. If an application is known to
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not need much DOS memory, this value could be set to the size of the memory
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required for the image, which provides roughly 0.5Mb additional memory before
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paging happens. This parameter is one I would expect might be adjusted when
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distributing an application for maximum performance on a wide variety of
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Paragraphs of DOS memory to reserve when 640K paging ? [3840]
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If the image needs to page in the DOS memory area (triggered by the parameter
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value above), this parameter tells how much DOS memory to save for DOS
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allocation requests. The value is in paragraphs (16 byte increments), so the
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default is 60Kbytes. You will actually end up with a bit more probably, since
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the page tables are allocated on 4Kbyte rounded boundaries. Some amount of
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DOS memory needs to be saved for potentially expanding the file table, the
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sbrk() algorithm, DMA buffers, etc. This amount can be tuned on an image
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by image basis, and may be as little as 0.
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Paragraphs of memory for extra CWSDPMI internal heap ? [256]
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CWSDPMI is built with an internal 4K heap. Each nested task consumes around
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300 bytes, each memory zone takes 12 bytes, and each HW interrupt (nested)
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takes around 850 bytes. If extra DOS memory is available, the additional
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paragraphs specified here are added to the heap at execution time by DOS.
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The 8K default should be good for up to 40Mb in small requests. If you
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compile very large C++ programs or allocate lots of memory in small pieces,
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you might need to bump this parameter. If you are very tight on memory,
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you could decrease it to zero and pick up another 4K of DOS memory. Each
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paragraph allows a little more than one more memory zone (or in the worse
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case around 85Kb of DPMI memory).
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Maximum size of swap file ? [128Mb]
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CWSDPMI dynamically allocates memory at run time for up to 2044Mb of swap file
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space. The bitmap for the swap usage requires 32 bytes of memory per 1Mb of
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swap usage. The default will provide up to 128Mb of swap space with a run
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time memory requirement of 4Kb DOS memory. The dynamic allocation is limited
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by the free space on the drive, so if you don't have much space on your hard
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drive, you don't need to worry about this. If you run small programs and want
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to save memory (maybe to stuff the allocation in a UMB) you can decrease this
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value. If you want to run monster programs needing 2Gb of address space you
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can increase this value (but this would increase the DOS memory usage). This
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value is ignored by CWSDPR0.
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Value of run option flags ? [0]
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There are a few run-time options in CWSDPMI which should not be needed by most
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users which can be activated by this field of bit flags:
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Bit 0 (1): Disable allocation of run time page tables in UMBs (low only)
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Bit 1 (2): Pre-allocate page table memory (in DPMI memory request)
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Bit 2 (4): Disable DPMI 1.0 extensions (Null page protection, mapping)
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Other values should be zero for future compatibility but are currently ignored.