Sun Microelectronics
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7. UltraSPARC External Interfaces
5. SC can pipeline some S_REPLYs that do not have an accompanying data
transfer (S_OAK, S_RTO, S_ERR), even while data is being transferred on
SYSDATA due to a previous S_REPLY. See Figure 7-28 on page 124. Even
though S_WBCAN or S_INAK do not have an accompanying data transfer,
SC cannot pipeline these S_REPLYs; SC must wait to issue S_WBCAN or
S_INAK until a cycle in which an S_WAB would be allowed.
6. SC can pipeline S_REPLY types that have an accompanying data transfer,
such that the SYSDATA bus can be kept continually busy without any dead
cycles, as long as the same source is driving the data. If sources are
switched, one dead cycle is required on SYSDATA; this allows the first
source to switch off before the next source can drive the data. The earliest
that the next source can drive the data is in the cycle following the dead
cycle; thus, the pipelining of data accompanying S_REPLY types to the sink
UltraSPARC is adjusted with one extra bubble for the dead cycle.
7. Figure 7-28 on page 124 shows the ordering of S_REPLYs for delivering
data to UltraSPARC.
Table 7-20 on page 122 specifies the S_REPLY types.
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