Central Processing Unit
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
3-39
subsequent instruction. Blockage refers to the interval from the time an instruction begins execution until
its execution unit is available for a subsequent instruction.
NOTE
When the blockage equals the latency, it is not possible to issue another
instruction to the same unit in the same cycle in which the first instruction
is being written back.
3.13
User Instruction Set Architecture (UISA)
3.13.1
Computation Modes
The RCPU is a 32-bit implementation of the PowerPC ISA architecture. Any reference in the PowerPC
ISA architecture books (UISA, VEA, OEA) regarding 64-bit implementations are not supported by the
core. All registers except the floating-point registers are 32 bits wide.
3.13.2
Reserved Fields
Reserved fields in instructions are described under the specific instruction definition sections. Unless
otherwise noted, reserved fields should be written with a zero when written and return a zero when read.
Thus, this type of invalid form instructions yield results of the defined instructions with the appropriate
field zero.
In most cases, the reserved fields in registers are ignored on write and return zeros for them on read on any
control register implemented by the MPC561/MPC563. Exception to this rule are bits [16:23] of the
fixed-point exception cause register (XER) and the reserved bits of the machine state register (MSR),
which are set by the source value on write and return the value last set for it on read.
Table 3-20. Instruction Latency and Blockage
Instruction Type
Precision
Latency
Blockage
Floating-point
multiply-add
Double
Single
7
6
7
6
Floating-point
add or subtract
Double
Single
4
4
4
4
Floating-point multiply
Double
Single
5
4
5
4
Floating-point divide
Double
Single
17
10
17
10
Integer multiply
—
2
1 or 2
1
1
Refer to Section 7, “Instruction Timing,” in the
RCPU Reference Manual
(RCPURM/AD) for details.
Integer divide
—
2 to 11
1
2 to 11
1
Integer load/store
—
See note
1
See note
1
Summary of Contents for MPC561
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