
S5335 – PCI Bus Controller, 3.3V
Revision 5.01 – November 30, 2005
Data Sheet
AMCC Confidential and Proprietary
DS1657 98
Initiator Preemption
A PCI initiator (bus master) is said to be preempted
when the system platform deasserts the initiator’s bus
grant signal, GNT#, while it still requests the bus
(REQ# asserted). This situation occurs if the initiator’s
latency timer expires and the system platform (bus
arbitrator) has a bus master request from another
device. The S5335 Master Latency Timer register con-
trols the S5335 responsiveness to the removal of a
bus grant (preemption). The presence of a Master
Latency Timer register can cause two preemption
situations:
1. Removal of GNT# when the latency timer is non-
zero (S5335 is guaranteed to still “own the bus”).
2. Removal of the GNT# after the latency timer has
expired.
The first situation is depicted in Figure 52, when the
latency timer has not expired. Preemption with a zero
or expired latency timer is shown in Figure 53.
Figure 52. Master Initiated Termination Due to Preemption and Latency Timer Active (S5335 as Master)
Figure 53. Master Initiated Termination Due to Preemption and Latency Timer Expired (S5335 as Master)
PCI CLOCK
GNT #
FRAME
IRDY#
TRDY#
S5335
LATENCY
TIMER
1
2
3
(T)
(I)
PREEMPTION
DATA
TRANSFERRED
(I)
5
4
DATA
TRANSFERRED
DATA
TRANSFERRED
DATA
TRANSFERRED
6
=3
=2
=1
=0
TIMEOUT
SENSED
(I) = DRIVEN BY INITIATOR
(T) = DRIVEN BY TARGET
PCI CLOCK
GNT #
FRAME
IRDY#
TRDY#
LATENCY
TIMER
1
2
3
(T)
(I)
PREEMPTION
DATA
TRANSFERRED
(I)
=0
=1
5
4
(I) = DRIVEN BY INITIATOR
(T) = DRIVEN BY TARGET
S5335