Page 60
Appendix B
Eagle 450 Upgrade Instructions, Rev. A00
When specifying write buffering for a device, two files are placed into system memory: .DVR
(loaded from disk) and .WRC (directly created in system memory), which are the driver and
cache buffer. This is true for all SCSI disk devices except the DSK device. For the DSK device,
the file DSK.DVR does not need to be created because it is already loaded into the system
monitor. Therefore, for the DSK device, only the file DSK.WRC will be created in system
memory.
In the three-drive example mentioned earlier, the added SYSTEM commands would look like this:
SYSTEM DVR:DSK/N 100K 60 ;Driver in AMOS will create DSK.WRC
SYSTEM DVR:SUB/N 100K 60 ;Load SUB.DVR and create SUB.WRC
This would set up 100K of write buffering for the DSK devices and 100K of write buffering for the SUB
device. All three drives would have their write buffers flushed every minute (or sooner if the drives are
not busy with read requests).
FINAL NOTES
Both read-ahead and write buffering schemes used on the AM-138 board dramatically improve system
performance in our lab tests. Both schemes are fine-tuned for the ColdFire processor and RISC SCSI
controller and do not take cycles away from AMOS like other commercially-available disk optimization
software.
Although our lab tests attempt to simulate the "real world" of user applications, they probably use the
resources of the AM-138 CPU and SCSI subsystem differently than your application does; therefore we
highly recommend you experiment with cache and write buffer sizes, read-ahead blocks, and flush
periods on an installed system to find the best possible combination for that system.
