Compaq EV68A Hwmfpr and Hwmtpr Instructions, 5describes the Hwret instruction fields, Hint, Stall

Opcodes Reserved for PALcode

Figure 6–3 HW_RET Instruction Format

31		26 25		21 20	16 15 14 13 12	0
OPCODE		RA		RB		DISP
HINT
STALL								FM-05656.AI4

Table 6–5describes the HW_RET instruction fields.

Table 6–5 HW_RET Instruction Fields Descriptions

Extent	Mnemonic	Value	Description
[31:26]	OPCODE	1E16	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	HW_JMP — The PC is not pushed onto the prediction stack. The predicted
			target is PC + (4*DISP[12:0]).
		01	HW_JSR — The PC is pushed onto the prediction stack. The predicted
			target is PC + (4*DISP[12:0]).
		10	HW_RET — The prediction is popped off the stack and used as the target.
		11	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/EV68A 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.

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 6–4shows the HW_MFPR and HW_MTPR instructions for- mat.

Figure 6–4 HW_MFPR and HW_MTPR Instructions Format

31 26 25 21 20 16 15 8 7 0

OPCODE

RA

RB

INDEX

SCBD_MASK

FM-05657.AI4

6–6 Privileged Architecture Library Code 21264/EV68A Hardware Reference Manual