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Multi-Layer AHB Crossbar Switch (XBAR)
MPC5644A Microcontroller Reference Manual, Rev. 6
202
Freescale Semiconductor
9.3
Function
This section describes in more detail the functionality of the XBAR.
9.3.1
Arbitration
The XBAR supports two arbitration schemes: a simple fixed-priority comparison algorithm and a simple
round-robin fairness algorithm. The arbitration scheme is independently programmable for each slave
port.
9.3.1.1
Fixed priority operation
When operating in fixed-priority mode, each master is assigned a unique priority level in the MPR (Master
Priority Register). If two masters both request access to a slave port the master with the highest priority in
the selected priority register will gain control over the slave port.
Any time a master makes a request to a slave port the slave port checks to see if the new requesting master’s
priority level is higher than that of the master that currently has control over the slave port (unless the slave
port is in a parked state). The slave port does an arbitration check at every clock edge to ensure that the
proper master (if any) has control of the slave port.
If the new requesting master’s priority level is higher than that of the master that currently has control of
the slave port the new requesting master will be granted control over the slave port at the next clock edge.
The exception to this rule is if the master that currently has control over the slave port is running a fixed
length burst transfer or a locked transfer. In this case the new requesting master will have to wait until the
end of the burst transfer or locked transfer before it will be granted control of the slave port. If the master
is running an undefined length burst transfer the new requesting master must wait until an arbitration point
for the undefined length burst transfer before it will be granted control of the slave port. Arbitration points
for an undefined length burst are defined in the MGPCR for each master.
If the new requesting master’s priority level is lower than that of the master that currently has control of
the slave port the new requesting master will be forced to wait until the master that currently has control
of the slave port either runs an IDLE cycle or runs a non IDLE cycle to a location other than the current
slave port.
9.3.1.2
Round-Robin priority operation
When operating in round-robin mode, each master is assigned a relative priority based on the master
number.This relative priority is compared to the ID of the last master to perform a transfer on the slave bus.
The highest priority requesting master will become owner of the slave bus as the next transfer boundary
(accounting for locked and fixed-length burst transfers). Priority is based on how far ahead the ID of the
requesting master is to the ID of the last master (ID is defined by master port number).
Once granted access to a slave port, a master may perform as many transfers as desired to that port until
another master makes a request to the same slave port. The next master in line will be granted access to
the slave port if the current master has no pending access request.
Summary of Contents for MPC5644A
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Page 24: ...MPC5644A Microcontroller Reference Manual Rev 6 24 Freescale Semiconductor...
Page 26: ...MPC5644A Microcontroller Reference Manual Rev 6 26 Freescale Semiconductor...
Page 52: ...Introduction MPC5644A Microcontroller Reference Manual Rev 6 52 Freescale Semiconductor...
Page 56: ...Memory Map MPC5644A Microcontroller Reference Manual Rev 6 56 Freescale Semiconductor...
Page 1228: ...Decimation Filter MPC5644A Microcontroller Reference Manual Rev 6 1228 Freescale Semiconductor...
Page 1440: ...FlexCAN Module MPC5644A Microcontroller Reference Manual Rev 6 1440 Freescale Semiconductor...