Fast Transfer Timing Example; Sysclk Cycles Between Sysaddout And Sysdata - Compaq 21264 Hardware Reference Manual

System Port
The command precedes data by at least one SYSCLK period. Table 4–25 shows the
number of SYSCLK cycles between SysAddOut and SysData for all system clock
ratios (clock forwarded bit times) and system framing clock multiples.
Table 4–25 SYSCLK Cycles Between SysAddOut and SysData
System framing clock ratio
1
2
4
Figure 4–5 show a simple example of a fast transfer. The data rate ratio is 1.5X with a
4:1 SYSCLK to INT_FWD_CLK ratio.
Figure 4–5 Fast Transfer Timing Example
SysAddOut_L[14:0]
SysData_L[63:0]
SYSCLK
SysAddOutClk_L
INT_FWD_CLK
GCLK
In fast data mode, movement of data into the 21264/EV67 requires turning around the
SysData bus that is being actively driven by the 21264/EV67. Given a SysDc fill com-
mand (ReadDataError, ReadData, ReadDataShared, ReadDataShared/Dirty, ReadData-
Dirty), the 21264/EV67 responds as follows:
1. Three GCLK cycles after perceiving the SysDc fill command, the 21264/EV67
turns off its drivers, interrupting any ongoing fast data write transactions.
2. The 21264/EV67 drivers stay off until the last piece of fill data is received, or a new
SysDc write command overrides the current SysDc fill command. It is the responsi-
bility of the external system to schedule SysDc fill or write commands so that there
is no conflict on the SysData bus.
3. The 21264/EV67 samples fill data in the GCLK clock domain, 10 +
SYSDC_DELAY GCLK cycles after perceiving the SysDc fill command. The
Cbox CSR SYSDC_DELAY[4:0] provides GCLK granularity for precisely placing
fills into the processor pipeline discussed in Section 2.2.
Cache and External Interfaces
4–32
GCLK/INT_FWD_CLK (Data Rate Ratio)
1.5X 2.0X 2.5X
4 3 2
2 2 1
1 1 1
Probe
Response
D0
3.0X 3.5X 4.0X 5.0X
2 2 2 1
1 1 1 1
1 1 1 1
D1 D2 D3 D4 D5
FM05822B.AI4
Alpha 21264/EV67 Hardware Reference Manual
6.0X 7.0X 8.0X
1 1 1
1 1 1
1 1 1
D6