Sable CPU Module Specification

3.2 Ebox
The Ebox contains the 64-bit integer execution datapath.
• Adder
• Logic box
• Barrel shifter
• Byte zapper
• Bypassers
• Integer multiplier
Copyright © 1993 Digital Equipment Corporation.
The integer multiplier retires four bits per cycle. The Ebox also contains the 32-entry
64-bit integer register file. The register file has four read ports and two write ports
that allow reading operands from and writing operands (results) to both the integer
execution datapath and the Abox.
3.3 Abox
The A-box in the 21064 contains six major sections:
• Address translation datapath
• Load silo
• Write buffer
• Dcache interface
• Internal processor registers (IPRs)
• External bus interface unit (BIU)
The address translation datapath has a displacement adder that generates the effective
virtual address for load and store instructions, and a translation buffer(S) that
generates the corresponding physical address.
3.3.1 Abox IPRs
Section 3.3.2 through Section 3.3.16 describe the registers contained within the 21064
processor’s A-box unit.
Functions Located on the DECchip 21064 37