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Application Note
(Includes Differences for 970FX to 970MP)
IBM PowerPC
®
970MP RISC Microprocessor Preliminary
5. Design Enhancements for PowerPC 970MP
Page 18 of 25
AppNote_970FX-MP_Differences_Body.fm.1.0
November 15, 2006
Table 5-2 describes the twelve power mode states.
5.3.2 Time Base and Decrementer
The time base and decrementer registers will run at a constant frequency, independent of changes to the
processor and bus frequencies. For 970FX, the default operation of these timers is to run at 1/8 the full
processor frequency, even when the processor itself is running at a lower frequency. For 970MP, the default
operation of these timers is to run at 1/16 the full processor frequency, even when the processor itself is
running at a lower frequency. When TBEN is configured to clock these timers (HID0[19] = 1), the timers will
run at the TBEN frequency. In this case, the maximum allowable TBEN frequency is 1/16 the full processor
frequency.
Since the mesh clock frequency can be lowered to 1/64th of the full-speed, the time base/decrementer may
be increased/decreased by more than one at a time. Therefore testing that the decrementer has reached the
value of zero in order to generate an internal interrupt is not sufficient. The logic detects that the counter has
wrapped around. Additionally the time resolution of the counters is limited by the mesh clock frequency.
5.4 I
2
C Bus Interface
5.4.1 Clock Dithering (New feature for 970FX DD3.0, enhanced in 970MP)
Input current to the processor can change significantly during power tuning frequency transitions. These
current changes must be controlled in order to avoid over and under-voltages that large di/dt might cause due
to inductance in the power distribution network. In DD3.0 of the 970FX, a clock dithering mechanism was
added in the power tuning hardware, to gradually transition between frequencies. The 970MP replaces the
970FX 24-bit dither with a selectable 24- or 48-bit dither pattern.
Table 5-2. Power Mode States
State Description
S1 Full Run, High Speed
S2 Doze, High Speed
S3 Nap, High Speed
S4 Deep Nap, High
S5 Full Run, Medium Speed
S6 Doze, Medium Speed
S7 Nap, Medium Speed
S8 Deep Nap, Medium
S9 Full Run, Low Speed
S10 Doze, Low Speed
S11 Nap, Low Speed
S12 Deep Nap, Low