Compaq 21264 - Manual (Page 190)

6–6 Privileged Architecture Library Code Alpha 21264/EV67 Hardware Reference Manual
Opcodes Reserved for PALcode
Figure 6–3 HW_RET Instruction Format
Table 6–5 describes the HW_RET instruction fields.
6.4.4 HW_MFPR and HW_MTPR Instructions
The HW_MFPR and HW_MTPR instructions are used to access internal processor reg-
isters. The HW_MFPR instruction reads the value from the specified IPR into the inte-
ger register specified by the RA field of the instruction. The HW_MTPR instruction
writes the value from the integer GPR, specified by the RB field of the instruction, into
the specified IPR. Figure 6–4 shows the HW_MFPR and HW_MTPR instructions for-
mat.
Figure 6–4 HW_MFPR and HW_MTPR Instructions Format
Table 6–5 HW_RET Instruction Fields Descriptions
Extent Mnemonic Value Description
[31:26] OPCODE 1E
16
The opcode value.
[25:21] RA — Register number. It should be R31.
[20:16] RB — Target PC of the HW_RET instruction. Bit [0] of the register’s contents
determines the new value of PALmode.
[15:14] HINT 00
01
10
11
HW_JMP — The PC is not pushed onto the prediction stack. The predicted
target is PC + (4*DISP[12:0]).
HW_JSR — The PC is pushed onto the prediction stack. The predicted
target is PC + (4*DISP[12:0]).
HW_RET — The prediction is popped off the stack and used as the target.
HW_COROUTINE — The prediction is popped off the stack and used as
the target. The PC is pushed onto the stack.
[13] STALL — If set, the fetcher is stalled until the HW_RET instruction is retired or
aborted. The 21264/EV67 will:
• Force a mispredict
• Kill instructions that were fetched beyond the HW_RET instruction
• Refetch the target of the HW_RET instruction
• Stall until the HW_RET instruction is retired or aborted
If instructions beyond the HW_RET have been issued out of order, they
will be killed and refetched.
[12:0] DISP — Holds a 13-bit signed longword displacement.
31 26 25 21 20 16 15 13 12 0
FM-05656.AI4
HINT
STALL
14
DISP RB RA OPCODE
31 26 25 21 20 16 15 0
FM-05657.AI4
8 7
SCBD_MASK RB RA OPCODE INDEX