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• These masters have write access to a portion of bank 1 when FlexNVM is used with
FlexRAM as EEPROM.
• For bank 0:
• Prefetch support for data and instructions is enabled for crossbar masters 0, 1, 2.
• The cache is configured for least recently used (LRU) replacement for all four
ways.
• The cache is configured for data or instruction replacement.
• The single-entry buffer is enabled.
27.5.2 Configuration options
Though the default configuration provides a high degree of flash acceleration, advanced
users may desire to customize the FMC buffer configurations to maximize throughput for
their use cases. When reconfiguring the FMC for custom use cases, do not program the
FMC's control registers while the flash memory or FlexMemory is being accessed.
Instead, change the control registers with a routine executing from RAM in supervisor
mode.
The FMC's cache and buffering controls within PFB0CR allow the tuning of resources to
suit particular applications' needs. The cache and two buffers are each controlled
individually. The register controls enable buffering and prefetching per access type
(instruction fetch or data reference). The cache also supports three types of LRU
replacement algorithms:
• LRU per set across all four ways,
• LRU with ways [0-1] for instruction fetches and ways [2-3] for data fetches, and
• LRU with ways [0-2] for instruction fetches and way [3] for data fetches.
As an application example: if both instruction fetches and data references are accessing
bank 0, control is available to send instruction fetches, data references, or both to the
cache or the single-entry buffer. Likewise, speculation can be enabled or disabled for
either type of access. If both instruction fetches and data references are cached, the
cache's way resources may be divided in several ways between the instruction fetches and
data references.
27.5.3 Wait states
Because the core, crossbar switch, and bus masters can be clocked at a higher frequency
than the flash clock, flash memory accesses that do not hit in the speculation buffer or
cache usually require wait states. The number of wait states depends on both of the
following:
1. the ratio of the core clock to the flash clock, and
Functional description
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
578
Preliminary
Freescale Semiconductor, Inc.
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