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MPC563XM Reference Manual, Rev. 1
Freescale Semiconductor
283
Preliminary—Subject to Change Without Notice
to instruction or data accesses. For the fixed partition, two configurations are supported. In one
configuration, buffers 0 and 1 are allocated for instruction fetches and buffers 2 and 3 for data accesses. In
the second configuration, buffers 0, 1 and 2 are allocated for instruction fetches and buffer 3 reserved for
data accesses.
11.7.9.4
Buffer Invalidation
The page read buffers may be invalidated under hardware or software control. Any falling edge transition
of the array’s
bkn_fl_done
signal causes the page read buffers to be marked as invalid. This input is
asserted by the Flash array at the beginning of all program/erase operations as well as in certain other cases.
Buffer invalidation occurs at the next AHB non-sequential access boundary, but does not affect a burst
from a page read buffer which is in progress. Software may also invalidate the buffers by clearing the
Bx_Py_BFE bit, which also disables the buffers. Software may then re-assert the Bx_Py_BFE bit to its
previous state, and the buffers will have been invalidated.
Also, the buffers are invalidated by hardware on any non-sequential (NSEQ) access with a non-zero value
on
haddr[28:24]
to support wait-state emulation.
11.7.10 Read-While-Write Functionality
The Flash BIU supports various programmable responses for read accesses while the Flash is busy
performing a write (program) or erase operation. For all situations, the Flash BIU uses the state of the Flash
array’s
bkn_fl_done
output to determine if it is busy performing some type of high-voltage operation,
namely, if
bkn_fl_done
= 0, the array is busy.
Specifically, there are two 3-bit read-while-write (BKn_RWWC) control register fields which define the
Flash BIU’s response to these types of access sequences. There are five unique responses that are defined
by the BKn_RWWC setting: one immediately reports an error on an attempted read and four settings that
support various stall-while-write capabilities. Consider the details of these settings.
•
BKn_RWWC = 0b0--
— For this mode, any attempted Flash read is a busy array is immediately terminated with an AHB
error response and the read is blocked in the controller and not seen by the Flash array.
•
BKn_RWWC = 0b111
— This defines the basic stall-while-write capability and represents the default reset setting. For
this mode, the Flash BIU module simply stalls any read reference until the Flash has completed
its program/erase operation. If a read access arrives while the array is busy or if a falling-edge
on
bkn_fl_done
occurs while a read is still in progress, the AHB data phase is stalled by
negating
hready_out
and saving the address and attributes into holding registers. Once the array
has completed its program/erase operation, the Flash BIU uses the saved address and attribute
information to create a pseudo address phase cycle to “retry” the read reference and sends the
registered information to the array as
bkn_fl_rd_en
is asserted. Once the retried address phase
is complete, the read is processed normally and once the data is valid, it is forwarded to the
AHB bus and
hready_out
negated to terminate the system bus transfer.
•
BKn_RWWC = 0b110
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