Compaq ECQD2KCTE Laptop User Manual


 
4–22 Alpha Architecture Handbook
4.3.3 Jumps
Format:
Operation:
{update PC}
va Rbv AND {NOT 3}
Ra PC
PC va
Exceptions:
Instruction mnemonics:
Qualifiers:
Description:
The PC of the instruction following the Jump instruction (the updated PC) is written to register
Ra and then the PC is loaded with the target virtual address.
The new PC is supplied from register Rb. The low two bits of Rb are ignored. Ra and Rb may
specify the same register; the target calculation using the old value is done before the new
value is assigned.
All Jump instructions do identical operations. They only differ in hints to possible branch-pre-
diction logic. The displacement field of the instruction is used to pass this information. The
four different "opcodes" set different bit patterns in disp<15:14>, and the hint operand sets
disp<13:0>.
These bits are intended to be used as shown in Table 4–4.
mnemonic Ra.wq,(Rb.ab),hint
!Memory format
None
JMP Jump
JSR Jump to Subroutine
RET Return from Subroutine
JSR_COROUTINE Jump to Subroutine Return
None