Text preview for : S90_Bus_Configuration_Rules.pdf part of arete_arix S90 Bus Configuration Rules . Rare and Ancient Equipment arete_arix s90 S90_Bus_Configuration_Rules.pdf
Back to : S90_Bus_Configuration_Rul | Home
PRELIMINARY
System90IXS Bus Configuration Rules
Revision 0.5
INTRODUCTION
Bus configuration rules are required for a numbez of reasons. Rules are required to ensure a balance of
system resources that minimize perfonnance bottlenecks. Rules are required to ensure that each module
is installed in a bus slot with enough priority to prevent module starvation in the event of bus resource
overload. Rules are required by cabling restraints that require that certain modules JlC.in$talled .in certain
slots. And rules are required to ensure that the power supply is not overloadc(L '.~".'
This paper covers configuration rules that deal with the balancing of system',iesoW'ces. and the assignment
of modules to ess and esslXA Bus slots.
ARBITRATION PRIORITY
The Bus Arbiter allocates ess or eSS/XA Bus resources to requesters according to requester priority.
The priority of a requester is determined by the bus slot it is installed in. Priorities are assigned to. bus
slots by the bus arbiter.
The 8f}. Bus Arbiter provides the bus arbiter function for the 8-slot ess Bus and assigns priorities to
CSS Bus slots as shown in the following table. For configuration purposes. slots 4 thought 7 are
considered mOH priority slots and slots 0 through 3 are considered LOW priority slots.
Arbitration Priority CSS Bu~ Slot(s)
Highest 7
6
5
4
3 and 0
Lowest 2 and 1
8f}. Bus Arbiter Priority Assignments
There are two Bus Arbiters that can provide the bus arbitrationfmiction for the 16..slot eSSor CSSIXA
Bus. the 16f}. Bus Arbiter and the 16/4 Bus Arbiter. The 16/2 Bus Arbiter is the original.desi811and may'
be used as the ess Bus arbiter in systems with no more than six 68020 Processor 'Modules ,or tw.o 68040
Dual Processor Modules. The 16/4 BuS. Arbiter provides more evenpriority