82433LX Datasheet, PDF (26/53 Pages) Intel Corporation – LOCAL BUS ACCELERATOR (LBX)

82433LX 82433NX
Figure 8 PIG 3 0 CPU-to-PCI Read Prefetch Buffer Commands
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Figure 8 shows an example of how the PIG com-
mands function on the PCI side The LCPRF com-
mand is driven on the PIG 3 0 lines until TRDY is
sampled asserted at the end of the fifth PCI clock
The LCPRA command is then driven until TRDY is
again sampled asserted at the end of the seventh
PCI clock TRDY is sampled asserted again so
LCPRB is driven only once Finally LCPRA is driven
again until the last TRDY is asserted at the end of
the tenth PCI clock In this way 4 Dwords are
latched in the read CPU-to-PCI prefetch buffer
Figure 8 also shows an example of how the HIG
commands function on the host side of the LBX
Two clocks after sampling the CPRF command the
LBX drives the host data bus The data takes two
cycles to become stable The first data driven in this
case is invalid since the data has not arrived on PCI
The data driven on the host bus changes in the sev-
enth host clock since the LCPRF command has
been driven on the PIG 3 0 lines the previous cycle
latching a new value into the first location of the read
prefetch buffer At this point the data is not the cor-
rect value since TRDY has not yet been asserted
on PCI The LCPRF command is driven again in the
fifth PCI clock while TRDY is sampled asserted at
the end of this clock The requested data for the
read is then latched into the first location of the read
prefetch buffer and driven onto the host data bus
becoming valid at the end of CPU clock 12 The
BRDY signal can therefore be driven asserted in
this clock The following read transaction (issued in
CPU clock 15) requests the next Dword and so the
CPRA command is driven on the HIG 4 0 lines ad-
vancing to read the next location in the read pre-
fetch buffer As the correct data is already there the
command is driven only once for this transaction
The next read transaction requests data in the same
Dword as the previous Therefore the CPRA com-
mand is driven again the buffer is not advanced
and the same Dword is driven onto the host bus
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