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User’s Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
gx_03.fm.(1.2)
March 27, 2006
Instruction-Cache and Data-Cache Operation
Page 141 of 377
3.6.2 Bus Operations Caused by Cache-Control Instructions
The cache-control, TLB management, and synchronization instructions supported by the 750GX can affect or
be affected by the operation of the 60x bus. The operation of the instructions can also indirectly cause bus
transactions to be performed, or their completion can be linked to the bus.
The dcbz instruction is the only cache-control instruction that causes an address-only broadcast on the 60x
bus. All other data cache-control instructions (dcbi, dcbf, dcbst, and dcbz) are not broadcast unless specifi-
cally enabled through the HID0[ABE] configuration bit. Note that dcbi, dcbf, dcbst, and dcbz do broadcast to
the 750GX’s L2 cache, regardless of HID0[ABE]. HID0[ABE] also controls the broadcast of the sync and
Enforce In-Order Execution of I/O (eieio) instructions.
The icbi instruction is never broadcast. No broadcasts by other masters are snooped by the 750GX (except
for dcbz kill block transactions). For detailed information on the cache-control instructions, see Chapter 2,
Programming Model, on page 57.
Table 3-4 provides an overview of the bus operations initiated by cache-control instructions. Note that the
information in this table assumes that the WIM bits are set to 001; that is, the cache is operating in write-back
mode, caching is enabled and coherency is enforced.
For additional details about the specific bus operations performed by the 750GX, see Chapter 8, Bus Inter-
face Operation, on page 279 in this manual.
Table 3-4. Bus Operations Caused by Cache-Control Instructions (WIM = 001)
Instruction Current Cache State Next Cache State Bus Operation Comment
sync Don’t care No change
sync
(if enabled in HID0[ABE])
Waits for memory queues to complete bus
activity.
tlbie — — None TLB invalidate entry.
tlbsync — — None
TLB synchronization. Waits for the nega-
tion of the TLBSYNC
input signal to com-
plete.
eieio Don’t care No change
eieio
(if enabled in HID0[ABE])
Address-only bus operation.
icbi Don’t care I None —
dcbi Don’t care I
Kill block
(if enabled in HID0[ABE])
Address-only bus operation.
dcbf I, E I
Flush block
(if enabled in HID0[ABE])
Address-only bus operation.
dcbf M I Write with kill Block is pushed.
dcbst I, E No change
Clean block
(if enabled in HID0[ABE])
Address-only bus operation.
dcbst M E Write with kill Block is pushed.
dcbz I M Write with kill —
dcbz E, M M Kill block Writes over modified data.
dcbt I E Read-with-intent-to-modify Fetched cache block is stored in the cache.
dcbt E, M No change None —
dcbtst I E Read-with-intent-to-modify Fetched cache block is stored in the cache.
dcbtst E,M No change None —