Sun Microelectronics
82
UltraSPARC User’s Manual
Figure 7-7
Timing for Coherent Writes with E-to-M State Transition (1–1–1 Mode)
Otherwise, the tag port is available for a tag check of a younger store during the
data write. In the timing diagram shown in Figure 7-5 on page 81, the store buffer
is empty when the first write request is made, which is why there is no overlap
between the tag accesses and the write accesses. In normal operation, if the line is
in M state, the tag access for one write can be done in parallel with the data write
of previous write (E state updates cannot be overlapped). This independence of
the tag and data buses make the peak store bandwidth as high as the load band-
width (one per cycle). Figure 7-8 shows the 1–1–1 Mode overlap of tag and data
accesses. The data for three previous writes (W0, W1 and W2) is written while
three tag accesses (reads) are made for three younger stores (R3, R4 and R5).
Figure 7-8
Timing Overlap: Tag Access / Data Write for Coherent Writes (1–1–1 Mode)
If the line is in Shared (S) or Owned (O) state, a read for ownership is performed
before writing the data.
CLK
CYCLE
0
1
2
3
4
5
6
7
8
9
TSYN_WR_L
R0
R1
R2
U0
U1
U2
TOE_L
R0
R1
R2
U0
U1
U2
ECAT
A0_tag
A1_tag
A2_tag
TDATA
D0_tag
D1_tag
D2_tag
DSYN_WR_L
W0
W1
W2
DOE_L
W0
W1
W2
ECAD
A0_data
A1_data
A2_data
EDATA
D0_data D1_data D2_data
D0_tag
D1_tag
D2_tag
A0_tag
A1_tag
A2_tag
CLK
CYCLE
0
1
2
3
4
5
6
7
TSYN_WR_L
R3
R4
R5
TOE_L
R3
R4
R5
ECAT
A3_tag
A4_tag
A5_tag
TDATA
D3_tag
D4_tag
D5_tag
DSYN_WR_L
W0
W1
W2
DOE_L
W0
W1
W2
ECAD
A0_data
A1_data
A2_data
EDATA
D0_data
D1_data
D2_data
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