Browse Prior Art Database

Method for Increasing the Number of Micro Channel Arbitration Levels

IP.com Disclosure Number: IPCOM000113743D
Original Publication Date: 1994-Sep-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 171K

Publishing Venue

IBM

Related People

Cheselka, HH: AUTHOR [+10]

Abstract

Operation: 1) Arbitrating participants drive -PREEMPT active to request use of the Micro Channel. 2) The CACP initiates an arbitration cycle by driving ARB/-GNT to the arb state (high level). 3) The arbitrating participants drive their 4-bit arb level onto the arb bus -ARB(0-3). When an arbiter detects a more-significant bit "low" on the arb bus s (other than one of (other than one of its own), it stops driving less-significant arb bits. The arbiter driving the lowest arb level (i.e., higher priority) thus wins control when ARB/-GNT goes to the grant state. to the grant state.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 36% of the total text.

Method for Increasing the Number of Micro Channel Arbitration Levels

       Operation:
  1) Arbitrating participants drive -PREEMPT active to request use
of the Micro Channel.
  2) The CACP initiates an arbitration cycle by driving ARB/-GNT to
the         arb state (high level).
  3) The arbitrating participants drive their 4-bit arb level onto
the         arb bus -ARB(0-3).
     When an arbiter detects a more-significant bit "low" on the arb
bus       s (other than one of
     (other than one of its own), it stops driving less-significant
arb
     bits.  The arbiter driving the lowest arb level (i.e., higher
     priority) thus wins control when ARB/-GNT goes to the grant
state.         to the grant state.
  4) The -BURST signal may be driven active "low" by the winning
arbiter       r to signal the CACP
     to signal the CACP that multiple bus transfer cycles need to be
     performed prior to an arbitration cycle.  The -BURST signal is
     held low until all transfer have been completed or until another
ed or until another
     bus requestor drives -PREEMPT active "low."

      Disclosed is a method for increasing the number of available
Micro Channel* arbitration levels from its maximum of sixteen without
requiring changes to either the Micro Channel adapters or to the
System Master's Central Arbitration Control Point.

      The Micro Channel arbitration function is ordinarily
implemented as shown in Fig. 1.  The Central Arbitration Control
Point (CACP) is responsible for controlling the arbitration cycles.
The arbitration bus is a parallel bus that consists of four lines
ARB(0-3), supporting up to sixteen arbitration levels.  The
arbitration cycles are controlled using three arbitration signals:
-PREEMPT, ARB/-GNT, and -BURST.  Arbitrating participants drive
-PREEMPT active to request use of the channel.  The CACP initiates an
arbitration cycle by driving ARB/-GNT to the ARB state.  The
requesting local arbiters then drive their four-bit arbitration level
onto the arbitration bus.

      Arbitration levels are designated as X'0' (the highest priority
level) through X'F' (the lowest priority level).  When a local
arbiter detects a more-significant arbitration bus bit "low" (other
than its own), it stops driving its less significant arbitration
bits.  Consequently, the local arbiter driving the highest priority
level at the end of the arbitration cycle wins control of the
channel.

   Described below and shown conceptually in Fig. 2, consists of
an extended arbitration and translation mechanism ("Exarb/Xlate")
which
is inserted into the arbitration ARB(0-3) bus and the -PREEMPT
signal.
The result is that the arbitration bus together with -PREEMPT is
divided
into segments.  One segment attaches directly to the CACP and System
Master functions.  Additional segments attach downstream to
arbitrating
Micro Channel feature adapters and to sys...