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IBM2520L8767
IBM Processor for ATM Resources
atmrm.chapt04.01
08/27/99
The Bus DRAM Cache Controller (BCACH)
Page 189 of 553
25
Flush Cache Line 1
Setting this bit will force a flush of cache line 1 if it is dirty. This bit will be reset by the
hardware when the flush completes.
24
Flush Cache Line 0
Setting this bit will force a flush of cache line 0 if it is dirty. This bit will be reset by the
hardware when the flush completes.
23
Use RXQUE Advice
When set, advice from the receive queue entity will cause the cache logic to fill a line with
the data from the start of the buffer that was just dequeued by the software. This should
improve performance by having the receive data available when the processor accesses
the buffer after the dequeue. To make best use of this feature, the code should access
the receive data shortly after the dequeue to avoid the data in the cache line from becom-
ing stale and being invalidated due to other cache functions. When reset, advice from the
receive queue entity will be ignored.
22
Ack RXQUE Immediately
When reset, advice from the receive queue entity will be acknowledged immediately
even if the cache is not able to perform the requested data fetch. In this case, the advice
will be lost, and the cache will not fetch the data until the processor requests it again.
When set, the advice from the receive queue entity will not be acknowledged until the
cache has actually latched the advice information. This guarantees that the advice will be
used, but may cause delays in the receive queue entities processing.
21
Enable Ping Pong Buffer Support
When reset, this bit will disable the two-line ping pong feature associated with consistent
sequential cache accesses. When set, a series of sequential accesses to packet memory
that would normally require more than two cache lines to be satisfied will be limited to
only two cache lines, regardless of the length of the transfer. This feature is intended to
improve cache performance by preventing cache lines that contain the most recently
used processor data from being flushed due to a long streaming access.
20
Disable Locking on Collisions
When set, this bit will prevent detected collisions from locking up the memory control
entity.
19
Enable automatic flush
When set, this bit will enable the automatic flush feature of the cache. The auto flush fea-
ture will force a flush of a cache line to be performed if a sequential write of the last 2
locations in the cache line is detected.
18
Force predictive fill/flush for
non-streaming accesses
When set, this bit will force the predictive fill/flush logic to operate on all accesses of the
cache and not just streaming accesses. When reset, the predictive fill logic will only be
activated for streaming accesses in the cache.
17-16
Reserved
Reserved
15-8
Predictive Fill Threshold
These bits set the threshold at which a predictive fill will be initiated. If all of these bits are
set to ‘1’, a predictive fill will be initiated on the first streaming access of a cache line,
regardless of which byte in the line is accessed. If this field is set to X’3F’ a predictive fill
will be initiated on any streaming access of bytes at offset X’2’ through X’7’ in the cache
line. If this field is set to X’03’ a predictive fill will be initiated on any streaming access of
bytes at offset X’6’ or X’7’ in the cache line. Setting the field to all zeros will disable pre-
dictive fills.
7-0
Timed Flush Time Out Value
These bits control the time-out value used to monitor dirty cache lines for inactivity. The
value loaded into these eight bits is the number of 240ns ticks that can occur without any
activity in a dirty cache line before the cache logic will force a flush of the line to main
memory. Setting these bits to all zeros disables the timed flush feature.
Bit(s)
Function
Description