PXS20RM Datasheet, PDF (315/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Crossbar Switch (XBAR)
1
2
3
4
5
6
7
8
9
hclk
m0 request
m2 request
m4 request
Highest
Priority
Requester
Address/Cntrl
owner
htrans
Master 0
XBAR
Master 0
IDLE
NSEQ
Master 2 None Master 4
XBAR Master 2 XBAR
IDLE
NSEQ
IDLE
None
Master 4
NSEQ
XBAR
IDLE
hready
Figure 15-6. High to low priority mastership change
When the slave port is programmed for round-robin mode of arbitration then the slave port will switch
masters any time there is more than one master actively making a request to the slave port. This will
happen because any master other than the one which presently owns the bus will be considered to have
higher priority. Figure 15-7 shows an example of round-robin mode of operation.
hclk
m0 request
m1 request
m4 request
m5 request
Highest
Priority
Requester
Address/Cntrl
owner
htrans
hready
1
2
3
4
Master 1 Master 4
XBAR Master 1
IDLE
NSEQ
Master 5
Master 4
NSEQ
5
6
7
Master 0
Master 5
NSEQ
Master 4
Master 0
NSEQ
8
9
10
Master 5
None
Master 4 Master 5 XBAR
NSEQ NSEQ IDLE
Figure 15-7. Round-robin mastership change
Freescale Semiconductor
PXS20 Microcontroller Reference Manual, Rev. 1
15-21