AMBA Crossbar Switch (XBAR)
14-6
Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
14.2.1.2
Slave General-Purpose Control Registers (XBAR_SGPCRn)
The XBAR_SGPCR
n
of a slave port controls several features of the slave port, including the following:
•
Round-robin or fixed arbitration policy for a particular slave port
•
Write protection of any slave port registers
•
Parking algorithm used for a slave port
The PARK field indicates which master port this slave port parks on when no active access attempts are
being made to the slave and the parking control field is set to park on a specific master.
XBAR_SGPCR
n
[PARK] must only be programmed to select master ports that are actually available on
the device, otherwise undefined behavior results. The low-power park feature can result in an overall
power savings if the slave port is not saturated; however, an extra clock of latency results whenever any
master tries to access a slave (not being accessed by another master) because it is not parked on any master.
The XBAR_SGPCR can only be accessed in supervisor mode with 32-bit accesses. After the RO (read
only) bit is set in the XBAR_SGPCR, the XBAR_SGPCR and the SBAR_MPR can only be read. Attempts
to write to them have no effect and results in an error.
NOTE
Some of the unused bits in the SGPCR
n
registers are writeable and readable,
but they serve no function. Setting any of these bits has no effect on the
operation of this module.
25–27
MSTR1
Master 1 priority. Set the arbitration priority for master port 1 on the associated slave port.
000 Master 1 has the highest priority when accessing slave port n.
101 Master 1 has the lowest priority when accessing slave port n.
110–111
Invalid values
28
Reserved, must be cleared.
29–31
MSTR0
Master 0 priority. Set the arbitration priority for master port 0 on the associated slave port.
000 Master 0 has the highest priority when accessing slave port n.
101 Master 0 has the lowest priority when accessing slave port n.
110–111
Invalid values
Table 14-3. XBAR_MPRn Descriptions (continued)
Field
Description
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Summary of Contents for PXR4030
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