Ppc Arbiter; Table 2-6. Ppc Arbiter Pin Assignments - Motorola MVME2400 Series Programmer's Reference Manual

Caution should be exercised when using this mode since the over-
!
generosity of bus ownership to the PPC master can be detrimental to the
host CPU's performance. The Bus Hog mode can be controlled by the
Caution
XMBH bit within the GCSR. The default state for XMBH is disabled.

PPC Arbiter

PHB has an internal PPC60x bus arbiter. The use of this arbiter is optional.
If the internal arbiter is disabled, then the PHB must be allowed to
participate in an externally implemented PPC60x arbitration mechanism.
The selection of either internal or external PPC arbitration mode is made
by sampling an RD line at the release of reset. Please see the section titled
PHB Hardware Configuration on page 2-49
PHB has been designed to accommodate up to four PPC60x bus masters,
including itself (HAWK), two processors (CPU0/CPU1) and an external
PPC60x master (EXTL). EXTL can be an L2 cache, a second bridge chip,
etc. When the PPC Arbiter is disabled, PHB will generate an external
request and listen for an external grant for itself. It will also listen to the
other external grants to determine the PPC60x master identification field
(XID) within the GCSR. When the PPC Arbiter is enabled, PHB will
receive requests and issue grants for itself and for the other three bus
masters. The XID field will be determined by the PPC Arbiter.
The PPC60x arbitration signals and their functions are summarized in the
following table.

Table 2-6. PPC Arbiter Pin Assignments

Pin Name Pin Type Reset
XARB0 BiDir Tristate
XARB1 BiDir Tristate
XARB2 BiDir Tristate
XARB3 BiDir Tristate
XARB4 Input
XARB5 Input
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Internal Arbiter
Direction Function
Output CPU0 Grant_
Output CPU1 Grant_
Output EXTL Grant_
Input CPU0 Request_
- - Input CPU1 Request_
- - Input EXTL Request_
Functional Description
for more information.
External Arbiter
Direction Function
Input CPU0 Grant_
Input CPU1 Grant_
Input EXTL Grant_
Output HAWK Request_
Input HAWK Grant_
Input - -
2-15
2