s5920 Applied Micro Circuits Corporation (AMCC), s5920 Datasheet - Page 133

• Manufacturer Part Number: s5920
• Description: Pci Product
• Manufacturer: Applied Micro Circuits Corporation (AMCC)

S5920 – PCI Product: Pass-Thru Operation
DQ outputs to float before Add-On logic attempts to
write to the Pass-Thru Read FIFO.
Clock 4: The BE[3:0]#, ADR[6:2], and SELECT#
inputs are asserted. WR# and DQ are asserted, indi-
cating that DATA1 is to be written to the PT Read FIFO
on the next clock. PTRDY# is asserted, to indicate the
completion of the current data phase.
Clock 5: As the S5920 samples WR# asserted, it
writes DATA1 into the PT Read FIFO. PTRDY# is sam-
pled asserted, which completes the first data transfer
and updates the internal FIFO pointers. The PTBE#
outputs are updated to indicate which bytes are valid
for the second transfer. The Add-On logic samples
PTBURST# asserted, so it knows more data is being
requested. The Add-On keeps WR# asserted, and
drives DATA2 onto the DQ bus. PTRDY# is also
asserted to complete the current data phase.
Clock 6: As the S5920 samples WR# asserted, it
writes DATA2 into the PT Read FIFO. PTRDY# is sam-
pled asserted, which completes the second data
transfer and updates the internal FIFO pointers. The
PTBE# outputs are updated to indicate which bytes
are valid for the third transfer. The Add-On logic sam-
ples PTBURST# asserted, so it knows more data is
being requested. The Add-On keeps WR# asserted,
and drives DATA3 onto the DQ bus. PTRDY# is also
asserted to complete the current data phase.
Clock 7: As the S5920 samples WR# asserted, it
writes DATA3 into the PT Read FIFO. PTRDY# is sam-
pled asserted, which completes the third data transfer
and updates the internal FIFO pointers. The PTBE#
outputs are updated to indicate which bytes are valid
for the last transfer. The S5920 deasserts PTBURST#,
indicating that the previous read was the second to
last. The next transfer from the Add-On bus will be the
last. The Add-On logic samples PTBURST# asserted,
so it knows more data is being requested. The Add-On
keeps WR# asserted, and drives DATA4 onto the DQ
bus. PTRDY# is also asserted to complete the current
data phase.
Clock 8: As the S5920 samples WR# asserted, it
writes DATA4 into the PT Read FIFO. PTRDY# is sam-
pled asserted, which completes the final data transfer
and updates the internal FIFO pointers. The S5920
deasserts PTATN#, indicating that the final transfer
was performed. No more data is being requested from
PCI. The Add-On logic samples PTBURST# deas-
serted, so it knows that the previous data transfer was
the last, and no more data is being requested. The
Add-On deasserts WR#, ADR[6:2], SELECT#,
BE[3:0]# and DQ. It also deasserts PTRDY#. Note that
in a synchronous design, the Add-On logic does not
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require PTATN# in order to terminate a Pass-Thru
read operation, PTBURST# is used for this.
Clock 9: As PTATN# and PTBURST# are deasserted,
the Pass-Thru access is complete, and the S5920 can
accept new Pass-Thru accesses starting on the next
clock. The other Pass-Thru signals can also change
state (in anticipation of a new transfer).
NOTE: With prefetch disabled, the performance of
Pass-Thru burst reads will be less than optimal.
Because of certain issues involving synchronizing sig-
nals across clock boundaries (ADCLK -> PCLK),
Pass-Thru burst reads will occur only in double and
single accesses. For example, a Pass-Thru burst read
of five data phases would translate to a burst-read of
two DWORDs, another burst-read of two DWORDs
followed by a single burst-read with PTATN# being
deasserted between each burst packet, losing poten-
tially valuable clock cycles. It is recommended to
enable prefetch if maximum performance is desired.
Figure 10 also shows a Passive Mode Pass-Thru burst
read, but the Add-On logic uses PTRDY# to control
the rate at which data is transferred. In many applica-
tions, Add-On logic is not fast enough to provide data
every ADCLK. In this example, the Add-On interface
writes data every other clock cycle.
Using PTRDY# to assert Wait-States
Clock 0: PCI address information is stored in the Pass-
Thru Address Register. The address is recognized as
a PCI read of Pass-Thru region 1. Add-On bus signals
PTATN#, PTBURST#, PTNUM[1:0], PTWR and
PTBE[3:0] will update on the next rising edge of
ADCLK.
Clock 1: Pass-Thru signals PTATN#, PTBURST#,
PTNUM[1:0], PTWR and PTBE[3:0] are driven to indi-
cate what action is required by Add-On logic. These
status signals are valid only when PTATN# is active.
Add-On logic can decode status signals upon the
assertion of PTATN#.
PTATN# Asserted. Indicates Pass-Thru access is
pending.
PTBURST# Asserted. The access has multiple data
phases.
PTNUM[1:0] 0h.Indicates. the access is to Pass-Thru
region 0.
PTWR Deasserted. Indicates the access is a read.
PTBE[3:0]# D1. Indicates valid bytes for the first data
transfer.
Clock 2: The Add-On logic has sampled PTATN# and
PTBURST# active, indicating that at least two read
data transfers are requested by the PCI. The Add-On
Revision 1.02 – April 12, 2007
Data Book
DS1596
133