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IDT Bus Arbitration
Theory of Operation
79RC32438 User Reference Manual
5 - 5
November 4, 2002
Notes
Figure 5.2 IPBus Arbitration Algorithm Flow Chart
*The fairness bit is used internally by the arbiter and is not visible to software
any bus master requesting
ownership of the bus with a
non-zero CMTC
any bus master requesting
ownership of the bus with a
zero CMTC
Grant ownership to the master with highest priority that is
requesting the bus. If multiple bus masters share the highest
priority, then choose one in a fair manner as follows:
a Select the bus master with the lowest index that
has highest priority, is requesting ownership of the
bus, and does not have its fairness bit set.*
b If all of these bus masters have their fairness bit
set, then clear the fairness bit of all bus masters
with highest priority and go back to step a.
Set the fairness bit of the bus master that is granted ownership
of the bus.
Decrement the CPTC of all priorities.
Decrement the CPTC of all priorities.
looping done
START
is CPTC for priority p equal
to zero
loop through all priorities
p = 0 through 3
Set the CPTC for priority p equal to its corresponding PTC.
For all bus masters with priority p, set their CMTC equal to the
corresponding MTC.
If the MF bit in the corresponding IPAPxC register is cleared,
then for all bus masters with priority p, clear the bus master’s
fairness bit.*
YES
NO
YES
NO
YES
YES
NO
NO
has the bus been
idle for 16 clock cycles
YES
NO
Grant ownership to the bus master with highest priority that is
requesting the bus and has a non-zero CMTC. If multiple
masters share these characteristics, then grant the bus to the
master that currently owns the bus. If none of the masters with
these characteristics currently own the bus, then grant the bus
to the master with the lowest index.
Decrement the CMTC of the bus master that was granted the
bus.
Decrement the CPTC of all priorities higher than or equal to the
priority of the master that was granted the bus.