Rainbow Electronics DS31256 - Manual (Page 136)

DS31256
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10.1.8 PCI Fast Back-to-Back
Fast back-to-back transactions are two consecutive bus transactions without the usually required idle
cycle (PFRAME and PIRDY deasserted) between them. This can only occur when there is a guarantee
that there is not any contention on the signal lines. The PCI specification allows two types of fast back-
to-back transactions—those that access the same agent (Type 1) and those that do not (Type 2).
Figure 10-9 shows an example of a fast back-to-back transaction where no idle cycle exists. As a bus
master, the Envoy is not capable of performing a Type 2 access. As a target, it can accept both types of
fast back-to-back transactions.
Figure 10-9. PCI Fast Back-To-Back
1 2 3 4 5 6 7 8 9 10
data #1 Address
CMD BE #1
PCLK
PFRAME
PAD
PCBE
PIRDY
PTRDY
PDEVSEL
data #2 data #2
BE #2 BE #2
Address data #1
CMD BE #1