Processor Status Signals; Quiescent Request (Qreq)-Output; Quiescent Acknowledge (Qack)-Input; Reservation (Rsrv)-Output - IBM PowerPC 750GX User Manual

7.2.11 Processor Status Signals

Processor status signals indicate the state of the processor. They include the memory reservation signal,
machine quiesce control signals, time-base enable signal, and TLB Invalidate Synchronize (TLBISYNC)
signal.
7.2.11.1 Quiescent Request (QREQ)—Output
State Asserted
Negated
Timing Assertion/
Negation
7.2.11.2 Quiescent Acknowledge (QACK)—Input
State Asserted
Negated
Timing Assertion/
Negation
Start-Up
7.2.11.3 Reservation (RSRV)—Output
State Asserted/
Negated
Timing Assertion/
Negation
gx_07.fm.(1.2)
March 27, 2006
Indicates that the 750GX is requesting all bus activity normally required to be
snooped to terminate or to pause so the 750GX can enter a quiescent (low
power) state. When the 750GX has entered a quiescent state, it no longer
snoops bus activity. See Chapter 10, Power and Thermal Management, on
page 335.
Indicates that the 750GX is not making a request to enter the quiescent
state.
Might occur on any cycle. QREQ will remain asserted for the duration of the
quiescent state.
Indicates that all bus activity has terminated or paused, and that the 750GX
might enter nap or sleep mode.
Indicates that the 750GX cannot enter nap or sleep mode, or that it must
return to doze mode from nap mode in order to snoop.
May occur on any cycle following the assertion of QREQ. Must be negated
for at least eight bus cycles prior to performing any snoop cycles to ensure
that the 750GX has returned to doze mode from nap mode.
See Table 7-6, Summary of Mode Select Signals, on page 274 for a descrip-
tion of the start-up function.
Represents the state of the internal reservation coherency bit used by the
lwarx and stwcx. instructions. See Section 8.7.1, Support for the lwarx and
stwcx. Instruction Pair, on page 319.
Might occur on any cycle. Will occur immediately following a transition of the
reservation coherency bit.
IBM PowerPC 750GX and 750GL RISC Microprocessor
User's Manual
Signal Descriptions
Page 273 of 377