
1-8
PowerPC Microprocessor Family: The Bus Interface for 32-Bit Microprocessors
The four columns under the heading, ‘a(chǎn)pplication’ in Table 1-2 are described as follows:
Basic operations—Signals in the column labeled ‘Basic’ in Table 1-2 are required to
build a simple, uniprocessor system with one bus, no external cache, and no support
for bus pipelining. Within this set of signals, TT4 is optional and, as shown in
Table 3-1, is used to identify additional transactions that can be snooped.
L2 cache support—Signals in the ‘L2’ column in Table 1-2 are required to support
an external cache. For example, TC[0–2] are necessary to indicate the type of
transaction. However, some of these signals are optional for some system designs.
For instance, a write-through external cache would not need the WT signal, or a
cache that responds only to burst operations would not need the CI signal.
Multiprocessor support—The signals GBL, SHD, and BG, listed in the ‘MP’
column, support memory coherency for systems with masters other than the
processor including multiprocessor systems. Chapter 4, “Memory Coherency,”
provides detailed information on memory coherency. The BG signal would be used
to assign the bus in systems in which the bus is shared by multiple devices, in which
case the GBL signal would be interconnected between all devices to ensure cache
coherency. Optionally the GBL and SHD signals could be connected to a bridge for
snooping. The bridge would set it to a known state.
TLBI synchronization
(TLBISYNC)
√
603: Indicates execution should stop after a
tlbsync
instruction
√
2.10.4
Power Management Signals
Quiescent request
(QUIESC_REQ)
√
601: Indicates the 601 is ready to enter a soft
stop state
√
2.11.1
System quiesced
(SYS_QUIESC)
√
601: Indicates to the 601 that the system is
ready for the soft stop state
√
2.11.2
Resume (RESUME)
√
601: Indicates to resume normal processing
√
2.11.3
Quiescent request
(QREQ)
√
603: Requests all bus activity requiring
snooping to pause
√
2.11.4
Quiescent acknowledge
(QACK)
√
603: Indicates all bus activity that requires
snooping has paused
√
2.11.5
Halted (HALTED)
√
604: Indicates the 604 has entered a low-power
state
√
2.11.6
Run (RUN)
√
604: Indicates to keep snooping in low-power
state
√
2.11.7
Table 1-2. Use and Reference for Bus Signals (Continued)
Signal
I
O
Function
Application
Section
Basic L2 MP Opt.