Motorola DSP96002 - Manual (Page 791)

MOTOROLA 9
2.6 CACHE OPERATING MODES
There are two main operating modes for the DSP96002: cache mode and PRAM mode.
They are both global, as they affect the internal program memory as a whole. When the
processor is in cache mode, each separate sector could be in one of two operating modes:
sector unlocked mode or sector locked mode. When the processor is in PRAM mode the
PRAM itself could be in one of two modes: PRAM enabled or PRAM disabled. Both in
cache mode and PRAM mode, the whole cache can be flushed by a software instruction.
The following list summarizes the DSP96002’s operating modes:
Cache Mode (global):
• Sector Unlocked Mode (per sector)
• Sector Locked Mode (per sector)
• Cache flush (global)
PRAM Mode (global):
• PRAM Enabled (global)
• PRAM Disabled (global)
• Cache flush (global)
2.6.1 Cache Mode
In the cache mode, accesses to the storage area of the sectors are done implicitly by in-
struction fetches or by MOVEM instructions. DMA references to and from program mem-
ory space (in the cache or external) are disabled in hardware.
2.6.1.1 Sector Unlocked Mode
When the processor is in the sector unlocked mode, the program memory sector is con-
figured as a regular cache sector. Sector replacement from that cache sector is allowed.
The cache controller will decide when to replace an external memory sector that resides
in a certain cache sector (sector miss), according to the cache controller LRU algorithm.
Unlocking a sector could happen in four different situations. In the first situation, the user
unlocks a specific cache sector by using the PUNLOCK instruction. In the second situa-
tion, the user unlocks all the cache sectors in the internal program memory by using the
PFREE instruction. In the third situation, the user unlocks all the cache sectors in the in-
ternal program memory as part of a cache flush by using the PFLUSH instruction. In the
forth situation, a hardware reset unlocks all the cache sectors.
A locked sector can be unlocked by the new special instructions PUNLOCK and PUN-
LOCKR. Their operand is an effective memory address. The memory sector containing
this address is allocated into a cache sector (if it is not already in a cache sector) and the