13.6.3.2 Main TLB

Misses from the instruction and data micro TLBs are handled by a unified main TLB. Accesses to the main TLB take a variable number of cycles, according to competing requests from each of the micro TLBs and other implementation-dependent factors.

The main TLB is 128-entry two-way set-associative.

TLB match process

Each TLB entry contains a virtual address, a page size, a physical address, and a set of memory properties. Each is marked as being associated with a particular application space (ASID), or as global for all application spaces. The CONTEXTIDR determines the currently selected application space.

A TLB entry matches when these conditions are true:

• Its virtual address matches that of the requested address.
• Its Non-secure TLB ID (NSTID) matches the Secure or Non-secure state of the MMU request.
• Its ASID matches the current ASID in the CONTEXTIDR or is global.

The operating system must ensure that, at most, one TLB entry matches at any time. The TLB can store entries based on the following block sizes:

Supersections, sections and large pages are supported to permit mapping of a large region of memory while using only a single entry in the TLB. If no mapping for an address is found within the TLB, then the translation table is automatically read by hardware and a mapping is placed in the TLB.