Wait State Control
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SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
FRAM Controller (FRCTL)
7.5.1 Wait State and Cache Hit
The FRAM controller contains a cache with two cache sets. Each of these cache sets contains two lines
that are preloaded with four words (64 bits) during one access cycle. An intelligent logic selects one of the
cache lines to preload FRAM data and preserves recently accessed data in the other cache. If one of the
four words stored in one of the cache lines is requested (a cache hit), no FRAM access occurs; instead, a
cache request occurs. No wait state is needed for a cache request, and the data is accessed with full
system speed. However, if none of the words that are available in the cache are requested (a cache
miss), the wait state controls the CPU to ensure proper FRAM access.
7.6
FRAM ECC
FRAM ECC supports bit error correction and uncorrectable bit error detection.
Correctable errors are generally single-bit errors that are detected and corrected by the hardware, so they
do not result in data corruption or system failure. The CBDIFG FRAM correctable bit error flag is set if a
correctable bit error has been detected and corrected. CBDIE can be used to enable an NMI event.
Uncorrectable bit errors are always multiple-bit errors, and they indicate memory corruption. The UBDIFG
FRAM uncorrectable bit error flag is set if an uncorrectable bit error has been detected in the FRAM error
detection logic. UBDRSTEN can be used to enable a power up clear (PUC) reset, or UBDIE can be used
to enable an NMI event. UBDRSTEN and UBDIE are mutually exclusive and are not allowed to be set
simultaneously.
For more information, refer to the
MSP430 FRAM Quality and Reliability
application report.
7.7
FRAM Write Back
All reads from FRAM requires a write back of the previously read content. This write back is performed
under all circumstances without any interaction from a user.
7.8
FRAM Power Control
The FRAM controller can disable the power supply for the FRAM array. By setting FRPWR = 0, the FRAM
array supply is disabled. Register accesses in the FRAM controller are still possible. Memory accesses
pointing into the FRAM address space automatically reset the FRPWR = 1 and re-enable the power
supply of the FRAM. A second control bit, FRLPMPWR, delays the power-up of the FRAM after LPM exit.
With FRLPMPWR = 1, the FRAM is activated directly on exit from LPM. FRLPMPWR = 0 delays the
activation of the FRAM to the first access into the FRAM address space. For LPM0, the FRAM power
state during LPM0 is determined from the previous state in active mode. If FRAM power is disabled, a
memory access automatically inserts wait states to ensure sufficient timing for the FRAM power-up and
access. Access to FRAM that can be served from cache does not change the power state of the FRAM
power control.
A PUC reset forces the state machine to Active mode with FRAM enabled. The CPU must execute from
RAM to clear the FRPWR bit for turning off power to FRAM.
shows the activation flow of the FRAM controller.