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86 www.xilinx.com PowerPC™ 405 Processor Block Reference Guide
1-800-255-7778 UG018 (v2.0) August 20, 2004
Chapter 2: Input/Output Interfaces
R
x The DCU activity is shown only as an aide in describing the examples. The occurrence
and duration of this activity is not observable on the DSPLB.
The following abbreviations appear in the timing diagrams:
DSPLB Three Consecutive Line Reads
The timing diagram in Figure 2-17 shows three consecutive eight-word line reads that are
address-pipelined between the DCU and BIU. It provides an example of the fastest speed
at which the DCU can request and receive data over the PLB. All reads are cacheable.
The first line read (rl1) is requested by the DCU in cycle 2. Data is sent from the BIU to the
DCU fill buffer in cycles 3 through 6. After all data associated with this line is read, it is
transferred by the DCU from the fill buffer to the data cache. This is represented by the fill1
transaction in cycles 7 through 9.
Table 2-17: DSPLB Timing Diagram Abbreviations
Abbreviation
a
Description Where Used
rl#, wl# Eight-word line read-request
or write-request identifier,
respectively
Request
Request acknowledge
Read-data acknowledge
Write-data acknowledge
(C405PLBDCUREQUEST)
(PLBC405DCUADDRACK)
(PLBC405DCURDDACK)
(PLBC405DCUWRDACK)
rw#, ww# Single word read-request or
write-request identifier,
respectively
Request
Request acknowledge
Read-data acknowledge
Write-data acknowledge
(C405PLBDCUREQUEST)
(PLBC405DCUADDRACK)
(PLBC405DCURDDACK)
(PLBC405DCUWRDACK)
adr# Data-access request address Request address (C405PLBDCUABUS[0:31])
d#
#
A doubleword (eight data
bytes) transferred as a result of
an eight-word line transfer
request
DCU read-data bus
DCU write-data bus
(PLBC405DCURDDBUS[0:63])
(C405PLBDCUWRDBUS[0:63])
d# A word (four data bytes)
transferred as a result of a
single word transfer request
DCU read-data bus
DCU write-data bus
(PLBC405DCURDDBUS[0:63])
(C405PLBDCUWRDBUS[0:63])
val Byte enables are valid Byte enables (C405PLBDCUBE[0:7])
flush# The DCU is busy performing a
flush operation
DCU
fill# The DCU is busy performing a
fill operation
DCU
Subscripts Used to identify the data
words transferred between the
BIU and DCU
Read-data acknowledge
DCU read-data bus
Write-data acknowledge
DCU write-data bus
(PLBC405DCURDDACK)
(PLBC405DCURDDBUS[0:63])
(PLBC405DCUWRDACK)
(C405PLBDCUWRDBUS[0:63])
# Used to identify the order
doublewords are sent to the
DCU
Transfer order (PLBC405DCURDWDADDR[1:3])
a. The “#” symbol indicates a number.