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FRAM ECC
Table 5-1. Manual Wait State Settings
f
MCLK
, MHz
NACCESS[2:0]
NPRECHG[2:0]
Number of wait states
8
0h
0h
0
16
1h
0h
1
20
2h
1h
3
24
2h
1h
3
5.5.2 Automatic Wait State Control
The automatic mode is the default mode, and after a boot the NAUTO bit is set to 1. The wait state is
controlled by an internal FRAM state machine, and the CPU is held when an access is executed. Manual
settings in the NACCESS and NPRECHG have no influence when the NAUTO bit is set. The wait state is
automatically adapted if an FRAM cache hit (as explained in
) occurs.
5.5.3 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 pre-loaded with four words (64 bits) during one access cycle. An intelligent logic selects one of
the cache lines to pre-load FRAM data and preserve 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 except
for a cache request. Upon a cache request, no wait state is needed and the data is accessed with full
system speed. However, if none of the words available in the cache are requested (a cache miss), the
wait state controls the CPU to ensure proper FRAM access.
5.5.4 Safe Access
The Safe Access is implemented to ensure correct FRAM access in Manual Wait State Mode.
Safe Access is active when the user configures the NACCESS[2:0] and NPRECHG[2:0] bits to values that
do not meet the required FRAM timing for the given clock setting. In this case, the Safe Access logic
ensures the correct timing for the access. The Access Time Error flag (ACCTEIFG) is set. A System NMI
(SYSNMI) occurs when ACCTEIE is set.
5.6
FRAM ECC
The FRAM supports bit error correction and uncorrectable bit error detection. The UBDIFG FRAM
uncorrectable bit error flag is set if an uncorrectable bit error has been detected in the FRAM memory
error detection logic. The CBDIFG FRAM correctable bit error flag is set if a correctable bit error has been
detected and corrected. UBDRSTEN enables a power-up clear (PUC) reset if an uncorrectable bit error is
detected. UBDIEN enables a NMI event if an uncorrectable bit error is detected. CBDIEN enables a NMI
event if a correctable bit error is detected and corrected.
246
FRAM Controller (FRCTL)
SLAU272C – May 2011 – Revised November 2013
Copyright © 2011–2013, Texas Instruments Incorporated