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Chapter 30 Flash Memory
MPC5606BK Microcontroller Reference Manual, Rev. 2
884
Freescale Semiconductor
30.8.8.4
Buffer invalidation
The page read buffers may be invalidated under hardware or software control.
At the beginning of all program/erase operations, the flash memory array will invalidate the page read
buffers. Buffer invalidation occurs at the next AHB non-sequential access boundary, but does not affect a
burst from a page read buffer that is in progress.
Software may invalidate the buffers by clearing the B
x
_P
y
_BFE bit, which also disables the buffers.
Software may then re-assert the B
x
_P
y
_BFE bit to its previous state, and the buffers will have been
invalidated.
One special case needing software invalidation relates to page buffer hits on flash memory data that was
tagged with a single-bit ECC event on the original array access. Recall that the page buffer structure
includes an status bit signaling the array access detected and corrected a single-bit ECC error. On all
subsequent buffer hits to this type of page data, a single-bit ECC event is signaled by the platform flash
memory controller. Depending on the specific hardware configuration, this reporting of a single-bit ECC
event may generate an ECC alert interrupt. In order to prevent repeated ECC alert interrupts, the page
buffers need to be invalidated by software after the first notification of the single-bit ECC event.
Finally, the buffers are invalidated by hardware on any non-sequential access with a non-zero value on
haddr[28:24] to support wait-state emulation.
30.8.9
Bank1 Temporary Holding Register
Recall the bank1 logic within the platform flash memory controller includes a single 128-bit data register,
used for capturing read data. Since this bank does not support prefetching, the read data for the referenced
address is bypassed directly back to the AHB data bus. The page is also loaded into the temporary data
register and subsequent accesses to this page can hit from this register, if it is enabled (B1_P0_BFE).
For the general case, a temporary holding register is written at the completion of an error-free flash
memory access and the valid bit asserted. Subsequent flash memory accesses that hit the buffer, that is, the
current access address matches the address stored in the temporary holding register, can be serviced in 0
AHB wait-states as the stored read data is routed from the temporary register back to the requesting bus
master.
The contents of the holding register are invalidated by the flash memory array at the beginning of all
program/erase operations and on any non-sequential access with a non-zero value on haddr[28:24] (to
support wait-state emulation) in the same manner as the bank0 page buffers. Additionally, the B1_P0_BFE
register bit can be cleared by software to invalidate the contents of the holding register.
Section 30.8.7, Flash error response operation
, the temporary holding register is
not
marked
as valid if the flash memory array access terminated with any type of transfer error. However, the result is
that flash memory array accesses that are tagged with a single-bit correctable ECC event are loaded into
the temporary holding register and validated. Accordingly, one special case needing software invalidation
relates to holding register hits on flash memory data that was tagged with a single-bit ECC event.
Depending on the specific hardware configuration, the reporting of a single-bit ECC event may generate
an ECC alert interrupt. In order to prevent repeated ECC alert interrupts, the page buffers need to be
invalidated by software after the first notification of the single-bit ECC event.
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