ADDRESS TRANSLATION LOOKASIDE BUFFER REPLACEMENT APPARATUS AND METHOD WITH USER OVERRIDE

A data processor (10) has a translation lookaside buffer, a "TLB," (56) for translating internal effective addresses into external real addresses. A user programmable bit in a special purpose register (68) controls which TLB entry in a group of entries will be replaced after an unsuccessful translation. Normally, the data processor uses a hardware controlled algorithm to select an entry for replacement. However, the user can overwrite the value in the special purpose register to force a certain replacement scheme. The user can thereby protect certain important translation mappings or deterministically test the TLB after manufacture.