Short: Makes A2091 work better in A4000; v0.2b Author: volker@vb.franken.de (Volker Barthelmann) Uploader: volker vb franken de (Volker Barthelmann) Type: driver/media Architecture: m68k-amigaos 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.