
Hawk PCI Host Bridge & Multi-Processor Interrupt Controller
MVME5100 Single Board Computer Programmer’s Reference (6806800H17B
)
76
2.3.2.5
PPC Arbiter
The 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. Refer to
information.
The 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 a
L2 cache, a second bridge chip, etc. When the PPC Arbiter is disabled, PHB generates an
external request and listen for an external grant for itself. It also listens to the other external
grants to determine the PPC60x master identification field (XID) within the GCSR. When the
PPC Arbiter is enabled, the PHB receives requests and issue grants for itself and for the other
three bus masters. The XID field is determined by the PPC Arbiter.
The PPC60x arbitration signals and their functions are summarized in the following table:
While RST_ is asserted, XARB0 through XARB4 is held in tri-state. If the internal arbiter mode
is selected, then XARB0 through XARB3 is driven to an active state no more than ten clock
periods after PHB has detected a rising edge on RST_. If the external arbiter mode has been
selected, then XARB4 is driven to an active state no more than ten clock periods after PHB has
detected a rising edge on RST_.
Table 2-7 PPC Arbiter Pin Assignments
Pin Name
Pin
Type
Reset
Internal Arbiter
External Arbiter
Direction Function Direction Function
XARB0
BiDir
Tristate
Output
CPU0 Grant_
Input
CPU0 Grant_
XARB1
BiDir
Tristate
Output
CPU1 Grant_
Input
CPU1 Grant_
XARB2
BiDir
Tristate
Output
EXTL Grant_
Input
EXTL Grant_
XARB3
BiDir
Tristate
Input
CPU0 Request_
Output
HAWK Request_
XARB4
Input
- -
Input
CPU1 Request_
Input
HAWK Grant_
XARB5
InpuT
- -
Input
EXTL Request_
Input
- -
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