
Prefetching SCRIPTS Instructions
2-9
Cache Line Size register value does not have any effect and the Memory
Read Line, Memory Read Multiple, and Memory Write and Invalidate
commands are not used.
The SYM53C895 may ush the contents of the prefetch buffer under
certain conditions, listed below, to ensure that the chip always operates
from the most current version of the software. When one of these
conditions apply, the contents of the prefetch buffer are ushed
automatically.
1.
On every Memory Move instruction.
The Memory Move instruction is often used to place modied code
directly into memory. To make sure that the chip executes all recent
modications, the prefetch buffer ushes its contents and loads the
modied code every time an instruction is issued. To avoid
inadvertently ushing the prefetch buffer contents, use the No Flush
option for all Memory Move operations that do not modify code within
the next 8 dwords. For more information on this instruction, refer to
Chapter 6.
2.
On every Store instruction.
The Store instruction may also be used to place modied code
directly into memory. To avoid inadvertently ushing the prefetch
buffer contents, use the No Flush option for all Store operations that
do not modify code within the next 8 dwords.
3.
On every write to the DSP.
4.
On all Transfer Control instructions.
When the transfer conditions are met, the prefetch buffer is ushed.
This is necessary because the next instruction to be executed is not
the sequential next instruction in the prefetch buffer.
5.
Prefetch Flush bit (DCNTL bit 6) is set.
The buffer ushes whenever this bit is set. The bit is self-clearing.
2.4.1 Op Code Fetch Burst Capability
Setting the Burst Op Code Fetch Enable bit in the DMODE register
(0x38) causes the SYM53C895 to burst in the rst two dwords of all
instruction fetches. If the instruction is a Memory to Memory move, the
third dword is accessed in a separate ownership. If the instruction is an