![](http://datasheet.mmic.net.cn/290000/XPC801ZP25_datasheet_16187868/XPC801ZP25_163.png)
Instruction Cache
9-12
MPC801 USER’S MANUAL
MOTOROLA
9
9.8 RESET SEQUENCE
To simplify the debug task of the system, the instruction cache is only disabled during
hardware reset (IC_CST
EN
= 0). This feature enables you to investigate the exact state of
the instruction cache prior to the event that asserts the reset. To ensure proper operation of
the instruction cache after reset, the unlock all, invalidate all, and instruction cache enable
commands must be issued.
9.9 DEBUG SUPPORT
The MPC801 can be debugged either in debug mode or by a software monitor debugger. In
both cases, the core asserts the internal freeze signal. When freeze is asserted the
instruction cache treats all misses as if they were from cache-inhibited
assuming the debug routine is not in the instruction cache, the cache state remains exactly
the same. When freeze is asserted, hits are still read from the array and the LRU bits are
updated. Therefore, in the simple case of the debug routine (if it is not already in the
instruction cache) it is read from memory like any other miss. For performance reasons, you
may prefer to run the debug routine from the cache by following these steps:
regions and,
1. Save both ways of the sets that are needed for the debug routine by reading the tag
value, LRU bit value, valid bit value, and lock bit value.
2. Unlock the locked ways in the selected sets.
3. Use load & lock to load and lock the debug routine into the instruction cache. Load &
lock operates the same when freeze is asserted.
4. Run the debug routine. All accesses to it will result in hits.
After the debug routine has completed, the old state of the instruction cache can be restored
by following these steps:
1. Unlock and invalidate all the sets that are used by the debug routine (both ways).
2. Use load & lock to restore the old sets.
3. Unlock the ways that were not previously locked.
4. To restore the old state of the LRU make sure the last access is made in the MRU way.
An access in this description is either load & lock or unlock.
9.9.1 Fetching Instructions From the Development Port
When the MPC801 is in debug mode, all instructions are fetched from the development port,
regardless of the address generated by the core. Therefore, the instruction cache is
bypassed when the MPC801 is in debug mode.