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TC1784
LMB External Bus Unit
User´s Manual
12-22
V1.1, 2011-05
EBUT13L-A, V1.16
The next cycle (Cycle n + 3) sees these parameters being passed to the appropriate
external access cycle state machine (used to select/initialize the appropriate external
access cycle, and also to select the external bus pins to be used for the access cycle).
12.7.6
Programming Sequence Locking
Programming sequences for some flash devices require that the source of the
programming transactions has exclusive access to the external memory device for the
duration of the write sequence. If such devices are used and can be accessed by multiple
transaction sources then the “Locked Programming Sequence” feature can be enabled
via register bit EBU_BUSWCON.LOCK_CS.
A programming sequence is considered to start when the processor data port carries out
an initial write transaction.
Note: It has been assumed that the processor data port is the only port that will ever
attempt programming operations to a NOR flash.
A programming sequence is considered to have ended when the processor data port
carries out a subsequent read transaction to a CS which it has locked, or when the
processor data port, which has locked CSx, carries out a write to CSy resulting in the
locking of CSy, or when an internal fail-safe timeout expires.
A programming sequence lock is aborted if an access is attempted from the processor
instruction port to the locked device. An aborted sequence will be flagged by the status
bit LCKABRT in the EBU_MODCON register. The LCKABRT flag will be cleared when
1
B
is written to the LCKABRT field.
Note: This is to prevent a system livelock in the event that the code running the
programming sequence is interrupted.
If programming sequence locking is enabled for CSx, then once a write transaction to
CSx is accepted from the processor data port, the LMB interface automatically “locks”
ownership of the device on CSx to that port. Any transaction requests (read or write) to
the same CSx from other transaction sources are retried until the end of the
programming sequence. Accesses to other CSy or CSz devices from the other initiators
will be permitted.
Sequence “locking” takes place in the LMB interface block.
The fail-safe timeout timer defaults to a count of 00
H
and is decremented at a frequency
of EBU_CLK/16. It commences counting from the preload value every time a write
completes. The default value can be changed by writing to the
EBU_BUSCON.LOCKTIMEOUT register field.
12.7.7
LMB Bus Width Translation
If the internal access width is wider than the external bus width specified for the selected
external region, the internal access is split in the EBU into several external accesses. For
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