PXN20RM Datasheet, PDF (432/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

AMBA Crossbar Switch (AXBS)
Table 16-4. XBAR_MPRn Descriptions (continued)
Field
MSTR2
Description
Master 2 priority. Set the arbitration priority for master port 2 on the associated slave port.
000 This master has the highest priority when accessing the slave port.
MSTR1
101 This master has the lowest priority when accessing the slave port.
110–111 Invalid values
Master 1 priority. Set the arbitration priority for master port 1 on the associated slave port.
000 This master has the highest priority when accessing the slave port.
MSTR0
101 This master has the lowest priority when accessing the slave port.
110–111 Invalid values
Master 0 priority. Set the arbitration priority for master port 0 on the associated slave port.
000 This master has the highest priority when accessing the slave port.
101 This master has the lowest priority when accessing the slave port.
110–111 Invalid values
16.2.1.2 Slave General-Purpose Control Registers (XBAR_SGPCRn)
The XBAR_SGPCRn 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_SGPCRn[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 XBAR_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 SGPCRn registers are writeable and readable,
but they serve no function. Setting any of these bits has no effect on the
operation of this module.
16-6
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor