S5935TFC AMCC [Applied Micro Circuits Corporation], S5935TFC Datasheet - Page 106

• Manufacturer Part Number: S5935TFC
• Description: PCI Product
• Manufacturer: AMCC [Applied Micro Circuits Corporation]

S5935 – PCI Product
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 S5935 Master Latency Timer register con-
trols the S5935 responsiveness to the removal of a
bus grant (preemption). The presence of a Master
Figure 52. Master Initiated Termination Due to Preemption and Latency Timer Active (S5935 as Master)
Figure 53. Master Initiated Termination Due to Preemption and Latency Timer Expired (S5935 as Master)
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PCI CLOCK
GNT #
FRAME
IRDY#
TRDY#
S5933 LATENCY
TIMER
DS1527
S5933
PCI CLOCK
GNT #
FRAME
IRDY#
TRDY#
LATENCY
TIMER
(I)
(T)
(I)
TRANSFERRED
=3
(T)
(I)
(I)
=1
DATA
1
=0
PREEMPTION
=2
PREEMPTION
1
TRANSFERRED
DATA
2
=1
2
3
=0
TRANSFERRED
DATA
TRANSFERRED
Latency Timer register can cause two preemption
situations:
The first situation is depicted in Figure 7, when the
latency timer has not expired. Preemption with a zero
or expired latency timer is shown in Figure 8.
TIMEOUT
SENSED
1. Removal of GNT# when the latency timer is non-
2. Removal of the GNT# after the latency timer has
DATA
zero (S5935 is guaranteed to still “own the bus”).
expired.
3
4
TRANSFERRED
DATA
4
(I) = DRIVEN BY INITIATOR
(T) = DRIVEN BY TARGET
Revision 1.02 – June 27, 2006
AMCC Confidential and Proprietary
(I) = DRIVEN BY INITIATOR
(T) = DRIVEN BY TARGET
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Data Book
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