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The MGPCRx[AULB] bits are the exception to this rule. The update of these bits is only
recognized when the master on that master port runs an IDLE cycle, even though the
slave bus cycle to write them will have already terminated successfully. If the
MGPCRx[AULB] bits are written between two burst accesses, the new AULB encodings
do not take effect until an IDLE cycle is initiated by the master on that master port.
18.3.3 Arbitration
The crossbar switch supports two arbitration schemes:
• A fixed-priority comparison algorithm
• A round-robin fairness algorithm
The arbitration scheme is independently programmable for each slave port.
18.3.3.1 Arbitration during undefined length bursts
Arbitration points during an undefined length burst are defined by the current master's
MGPCR[AULB] field setting. When a defined length is imposed on the burst via the
AULB bits, the undefined length burst is treated as a single or series of single back-to-
back fixed-length burst accesses.
The following figure illustrates an example:
Lost control Lost control
Master-to-slave
transfer
1
2
3
4
5
6
7
8
9 10
11
12
1 beat 1 beat 12 beat burst
No arbitration Arbitration allowed No arbitration No arbitration
MGPCR[AULB]
Figure 18-28. Undefined length burst example
In this example, a master runs an undefined length burst and the MGPCR[AULB] bits
indicate arbitration occurs after the fourth beat of the burst. The master runs two
sequential beats and then starts what will be a 12-beat undefined length burst access to a
new address within the same slave port region as the previous access. The crossbar does
not allow an arbitration point until the fourth overall access, or the second beat of the
second burst. At that point, all remaining accesses are open for arbitration until the master
loses control of the slave port.
Assume the master loses control of the slave port after the fifth beat of the second burst.
After the master regains control of the slave port no arbitration point is available until
after the master has run four more beats of its burst. After the fourth beat of the now
Functional Description
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
358
Preliminary
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