Compaq EV68A specifications Cmov Decomposed

Performance Counter Support

The CMOV instruction is decomposed into two valid fetched instructions that, in the absence of stalls, are fetched in consecutive cycles. See Table 6–12for more informa- tion.

Table 6–12 CMOV Decomposed

Instruction	New Instructions
CMOV Ra, Rb--> Rc	CMOV1 Ra, oldRc −−> newRc1
	CMOV2 newRc1, Rb −−> newRc2

6.10.3.2Operation

1.Setup

The following IPRs need to be set up by using PALcode instructions.

IPR Name	Relevant Fields	Meaning
IER_CM	PCEN[1:0]	Enable Interrupts.
PCTX	PPCE	Enable Process Performance Counting or use I_CTL[SPCE].
PCTR_CTL	SL0	Selects Aggregate or ProfileMe mode; set to 1 for ProfileMe mode.
	SL1	Selects PCTR0 and PCTR1 counting modes. See Table 6–14for more infor-
		mation.
	PCTR0[19:0]	Set counter 0 value (2**20-N). This selects approximately the Nth valid
		fetched instruction as the profiled instruction. Because writes to PCTR0 are
		incremented by 0..4, the profiled instruction is one of the (N-4)th to Nth valid
		fetched instructions. See Section 6.10.1 for more setup precautions.
	PCTR1[19:0]	Set counter 1 value = 0. See Section 6.10.1 for more setup precautions.
I_CTL	SPCE	Enable System Performance Counting or use PCTX[PPCE].
	PCT0_EN	Enable performance counter 0.
	PCT1_EN	Enable performance counter 1.

2.Open window

PCTR0 accumulates up to 4 valid fetched instructions per cycle when enabled via I_CTL[PCT0_EN] and either I_CTL[SPCE] or PCTX[PPCE].

The valid fetched instruction that causes PCTR0 to overflow opens the window and becomes the profiled instruction and covers a period of time near to when the instruction was in flight. The first cycle of the window is the 5th cycle after the instruction was fetched. A residual count of up to 7 valid fetched instructions is accumulated in PCTR0 in the two cycles between overflow and the start of the Pro- fileMe window. This residual count is returned in I_STAT[overcount(2,0)].

3.Count

If PCTR0 and PCTR1 are enabled, they increment according to modes selected by SL0 & SL1.

4.End window

The last cycle of the window depends on whether the instruction traps, retires, aborts, and/or is squashed by the fetcher.

21264/EV68A Hardware Reference Manual Privileged Architecture Library Code 6–21