Compaq EV68A Ibox IPRs, ITB Tag Array Write Register Itbtag, ITB PTE Array Write Register Itbpte

Ibox IPRs

Figure 5–6 Virtual Address Format Register (VA_48 = 1, VA_FORM_32 = 0)

63 43 42 38 37

VPTB[63:43]

SEXT(VA[47])

VA[47:13]

3 2 0

LK99-0012A

Figure 5–7shows VA_FORM when VA_CTL(VA_48) equals 0 and

VA_CTL(VA_FORM_32) equals 1.

Figure 5–7 Virtual Address Format Register (VA_48 = 0, VA_FORM_32 = 1)

63 30 29 22 21 3 2 0

VPTB[63:30]

VA[31:13]

LK99-0013A

5.2 Ibox IPRs

This section describes the internal processor registers that control Ibox functions.

5.2.1 ITB Tag Array Write Register – ITB_TAG

The ITB tag array write register (ITB_TAG) is a write-only register. The ITB tag array is written by way of this register. A write transaction to ITB_TAG writes a register out- side the ITB array. When a write to the ITB_PTE register is retired, the contents of both the ITB_TAG and ITB_PTE registers are written into the ITB entry. The specific ITB entry that is written is determined by a round-robin algorithm; the algorithm writes to entry number 0 as the first entry after the 21264/EV68A is reset. Figure 5–8shows the ITB tag array write register.

Figure 5–8 ITB Tag Array Write Register

63 48 47 13 12 0

VA[47:13]

LK99-0015A

5.2.2 ITB PTE Array Write Register – ITB_PTE

The ITB PTE array write register (ITB_PTE) is a write-only register through which the ITB PTE array is written. A round-robin allocation algorithm is used. A write to the ITB_PTE array, when retired, results in both the ITB_TAG and ITB_PTE arrays being written. The specific entry that is written is chosen by the round-robin algorithm described above. Figure 5–9shows the ITB PTE array write register.

5–6 Internal Processor Registers 21264/EV68A Hardware Reference Manual