WHAT'S NEW

    This version contains several bugfixes, new options/features and includes
    source.

INTRODUCTION

    ZorroII boards can only reach the lower 16MB of address space. So DMA
    SCSI controllers must find another way to transfer data to expansion
    RAM. Some of them (especially the A2091) do a very bad job in this
    situation. In an A4000/40 transfer rates may drop to 50KB/s.
    This program patches the (2nd.)scsi.device to use MEMF_24BITDMA
    RAM as a buffer followed (in case of CMD_READ) by CopyMem().
    It was developed with the A4000/A2091 combinbation in mind, but
    should work with other configurations, too (see REQUIREMENTS).

FEATURES

    There are already some PD utilities floating around that do a similar
    job. So why may this one be better?

    - It patches the device instead of the Read() & Write() DOS-functions,
      giving the following advantages:

      o Programs accessing the device directly (e.g. SysInfo, SCSI-Speed
        or tape-handlers) are patched, too.
      o Patching Read() doesn't seem to have any influence on LoadSeg(), so
        those patches don't speedup loading of programs whereas vb2091 does.
      o It is possible to use double-buffering and load into one buffer
        while copying the contents of the other one to fastram. This makes
        higher transfer rates possible. I wasn't able to get more than
        800KB/s with DOS-level-patches, but could get over 1MB/s with
        vb2091.

    - Some early A4000s (including mine :-( ) can't do DMA to onboard ram.
      On such A4000s every transfer to/from chipmem will cause the
      computer to hang. vb2091 can be told to redirect those transfers too.

 PERMSSN    UID  GID    PACKED    SIZE  RATIO METHOD CRC     STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                 4029    8372  48.1% -lh5- 50e7 Feb 21  1995 vb2091
[generic]                 2653    9668  27.4% -lh5- 2da9 Feb 21  1995 vb2091.c
[generic]                 3996    9220  43.3% -lh5- ea7c Feb 21  1995 vb2091.doc
[generic]                 2871    4708  61.0% -lh5- 5eb3 Feb 13  1995 vb2091SAS
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total         4 files   13549   31968  42.4%            Feb 22  1995