Freescale Semiconductor DSP56364 Manual de usuario Pagina 47

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Internal Memory Configuration
DSP56364 24-Bit Digital Signal Processor Users Manual, Rev. 2
Freescale Semiconductor 3-5
3.3.3 Dynamic Memory Configuration Switching
The internal memory configuration is altered by remapping RAM modules from Y data memory into
program memory space and vice-versa. The contents of the switched RAM modules are preserved.
The memory can be dynamically switched from one configuration to another by changing the MS bit in
OMR. The address ranges that are directly affected by the switch operation are specified in Table 3-3. The
memory switch can be accomplished provided that the affected address ranges are not being accessed
during the instruction cycle in which the switch operation takes place. For trouble-free dynamic switching,
no accesses (including instruction fetches) to or from the affected address ranges in program and data
memories are allowed during the switch cycle.
NOTE
The switch cycle actually occurs three instruction cycles after the
instruction that modifies the MS bit.
Any sequence that complies with the switch condition is valid. For example, if the program flow executes
in the address range that is not affected by the switch, the switch condition can be met very easily. In this
case a switch can be accomplished by just changing the MS bit in OMR in the regular program flow,
assuming no accesses to the affected address ranges of the data memory occur up to three instructions after
the instruction that changes the OMR bit. Special care should be taken in relation to the interrupt vector
routines since an interrupt could cause the DSP to fetch instructions out of sequence and might violate the
switch condition.
Special attention should be given when running a memory switch routine using the OnCE port. Running
the switch routine in trace mode, for example, can cause the switch to complete after the MS bit change
while the DSP is in debug mode. As a result, subsequent instructions might be fetched according to the
new memory configuration (after the switch), and thus might execute improperly.
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