Sun Microsystems UltraSPARC-I User Manual page 140

Thus, the sourcing of the first quadword is always with respect to the
S_REPLY. Data_Stall determines the number of clock cycles that the
quadword stays on SYSDATA (that is, the number of stalls). Figure 7-29
shows the data stall timing to UltraSPARC sourcing data.
2. When UltraSPARC is sinking data, SC can assert Data_Stall in the same
system clock cycle that the S_REPLY is asserted. The assertion of Data_Stall
delays latching of the quadword being received on SYSDATA during the
following system clock.
Thus, the latching of any quadword (including the first quadword) at the
sink UltraSPARC can be delayed for an arbitrary number of clock cycles by
keeping Data_Stall asserted for that many clock cycles. Figure 7-30 shows
the data stall timing to UltraSPARC sinking data.
3. SC cannot assert Data_Stall if there is no data transfer accompanying the
S_REPLY (S_WBCAN, S_OAK, S_INAK, S_RTO, S_ERR).
The data stall rules also apply to single quadword transfers (noncached
reads or writes).
S_REPLY to Data Source
Data on Bus
Data Stall
Figure 7-29 Data_Stall to UltraSPARC Sourcing Data
In Figure 7-29 the quad-word D
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
7. UltraSPARC External Interfaces
S_REPLY
1 clock
is held valid for one extra clock cycle.
0
D[0] D[1] D[2] D[3]