C5.2 Encoding for tag and data in the L1 instruction cache

The following table shows the format of the Instruction Cache Tag Read Operation Register and the Instruction Cache Data Read Operation Register.

The set-index range parameter (S) is determined by the following formula:

S = log2(size of the instruction cache in bytes / 2)

Table C5-2 Instruction cache tag and data location encoding

Bit field Description
[31] Cache Way
[30:S] Unused
[S-1:6] Set index
[5:2] Line offset
[1:0] Unused

The following table shows the format of the information in Data Register 0 following an Instruction Cache Tag Read Operation.

Table C5-3 Instruction cache tag data format

Bits Description
[31] Unused.

Valid and set mode:

[28] Non-secure state (NS).
[27:0] Tag address.

The Instruction Cache Data Read Operation returns two entries from the cache in Data Register 0 and Data Register 1 corresponding to the 16-bit aligned offset in the cache line:

Data Register 0Bits[19:0] data from cache offset+ 0b00.
Data Register 1Bits[19:0] data from cache offset+ 0b10.

In A32 state these two fields combined always represent a single predecoded instruction. In T32 state, they can represent any combination of 16-bit and partial or full 32-bit instructions.

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