A2091 14Mhz SCSI mod

[Dale423]

So with the BigRam2630 and the v6 SCSI2SD running The A2091toFast and Vbak2091 I am getting 1.6mb/sec (SysInfo). Without the BigRam2630 installed I get 2.6mb/sec. So the 112MB of the BigRam is causing some issues with the memory used for DMA. Not sure there is a way to force it to use the RAM on the 2091. Would like to get 2.6mb with the BigRam installed

 

[dorken]

The max. theoretical transferrate for async SCSI is 3,3MB/sec, Sync SCSI is 5MB/sec but ZII limit it to 3,5MB/sec, so real 2,6MB/sec is not bad, but also not optimal.
With Bigram installed the CPU has to copy the Data from 24Bit DMA memory into the 32Bit "Upper" Memory, this halves the max reachable transfer rate to 1,75MB/sec (1/2 ZII bandwidth) so 1,6MB/sec is not bad. To be able to reach the maximum really all settings must optimized to the max..

What could still be tried is:
- Optimize the Transfer to ZII, i.e. check if Sync Transfer is enabled, try a different MASK, i.e. 0xffffff or 0xfffffe or even 0xfffffc to get higher transferrates from Drive to ZII Mem. I dont know the V7 ROM limit, but with GururROM the A2091 is able reach the ZII Bus limit.
- A CopyMem replacement for 68030 CPU (e.g. CMQ030). Since the OS CopyMem is not highly optimized (even in 3.1.4) this sometimes give a noticeable difference with copies between ZII to 32Bit memory but here it could only give a little Boost because the ZII Bandwidth is the real bottleneck.

 

[Dale423]

Where would I look for Sync Transfer? I get the other stuff and will try it.

The max. theoretical transferrate for async SCSI is 3,3MB/sec, Sync SCSI is 5MB/sec but ZII limit it to 3,5MB/sec, so real 2,6MB/sec is not bad, but also not optimal.
With Bigram installed the CPU has to copy the Data from 24Bit DMA memory into the 32Bit "Upper" Memory, this halves the max reachable transfer rate to 1,75MB/sec (1/2 ZII bandwidth) so 1,6MB/sec is not bad. To be able to reach the maximum really all settings must optimized to the max..

What could still be tried is:
- Optimize the Transfer to ZII, i.e. check if Sync Transfer is enabled, try a different MASK, i.e. 0xffffff or 0xfffffe or even 0xfffffc to get higher transferrates from Drive to ZII Mem. I dont know the V7 ROM limit, but with GururROM the A2091 is able reach the ZII Bus limit.
- A CopyMem replacement for 68030 CPU (e.g. CMQ030). Since the OS CopyMem is not highly optimized (even in 3.1.4) this sometimes give a noticeable difference with copies between ZII to 32Bit memory but here it could only give a little Boost because the ZII Bandwidth is the real bottleneck.

 

[dorken]

The A2091 should pay attention to the sync flag in the RDB so the best option would be to edit it and set the Flag permanent.
Most newer Partition Tool can set this flag, but mix up different tools can completely destroy the RDB, so better be careful and always make a backup of the RDB!
There are also some some Commandline Toola like RDB or RDBFlags, this tools usually work with RDB from all Partitiontools, but a Backup cant hurt...

An other option is to use a Commandline tool like omniscsictrl or myunitcontrol and set the sync transfer in Startup-Sequence at every start, but i dont know if this tools word with original A2091 ROM...

In Post #36 (https://www.amibay.com/showthread.php?14706-A2091-14Mhz-SCSI-mod&p=400162&viewfull=1#post400162) it was mentioned that J5-4 must be set in order to activate the synchronous mode.