Owner`s manual

Page 6-2 Chapter 6

6.3THE SCSI DISPATCHER

All newer Alpha Micro computers (AM-4000, Roadrunners, Eagles, and later) use a

SCSI dispatcher program to communicate with the SCSI controller chip.

For each type of computer, there are two versions of the SCSI dispatcher: the "simple"

dispatcher and the "enhanced" (PIC-encoded) dispatcher. The simple dispatcher is only

intended to initially bring up a new or upgraded system; to make a warm-boot tape; or

for temporary situations on computers which do not have an SSD chip. It does not

support enhanced SCSI functions and is not meant for normal system operation. The

enhanced SCSI dispatcher supports additional SCSI features such as command

queueing, synchronous transfers, and multi-threaded and scatter-gather operations. The

enhanced dispatcher provides a tremendous performance increase over the simple

dispatcher. The SCSI dispatcher supports up to seven SCSI devices on the same bus,

or fifteen devices on a Wide-SCSI bus.

The enhanced dispatcher uses the same PIC code as the AMOS

monitor

. Once you

enter the monitor PIC code to enable the requested number of users, and define the

enhanced dispatcher in your system initialization file, the dispatcher is also enabled.

If you have

any

SCSI peripherals attached to the SCSI port on a dispatched computer,

you MUST define the SCSI dispatcher in your boot INI, regardless of whether you are

using SCSI-1 or SCSI-2 peripheral devices.

The name of the dispatcher depends on the type of computer:

System Type Enhanced Dispatcher Simple Dispatcher

Roadrunner 030 and 040,

Eagle 100-550

SCZRR SIMRR

AM-4000, AM-4000M, and

AM-3000 with AM-540

SCZ190 SIM190

Roadrunner 060, AM-6000 SCZR60 SIMR60

To define the SCSI dispatcher in your system initialization file enter:

SCZDSP xxxxxx.SYS

xxxxxx

is the name of the dispatcher version for your computer, as stated above. For

example:

SCZDSP SCZRR.SYS ;Enable enhanced SCSI dispatcher

The SCZDSP statement must come after the last TRMDEF statement and before the

first DEVTBL statement.

The SCZRR and SCZ190 dispatchers accept one command line switch, which is used

mainly in troubleshooting situations. As stated previously, the enhanced dispatchers

support synchronous data transfer. Under normal conditions the dispatcher attempts to

communicate with the drive in synchronous mode, and, if unsuccessful, switches to

non-synchronous mode automatically. However, you can force these dispatchers to

System Operator’s Guide to the System Initialization Command File, Rev. 03