Instruction Performance - Intel NIOS II Owner Reference Manual

The D-stage stall occurs if an instruction is trying to use the result of a late result
instruction too early and no M-stage pipeline flush is active. The late result
instructions are loads, shifts, rotates,
supported), divides (if hardware divide is supported), and multicycle custom
instructions (if present).
5.2.7.2. Branch Prediction
The Nios II/f core performs dynamic and static branch predictions to minimize the
cycle penalty associated with taken branches.

5.2.8. Instruction Performance

All instructions take one or more cycles to execute. Some instructions have other
penalties associated with their execution. Late result instructions have two cycles
placed between them and an instruction that uses their result. Instructions that flush
the pipeline cause up to three instructions after them to be cancelled. This creates a
three-cycle penalty and an execution time of four cycles. Instructions that require
Avalon-MM transfers are stalled until any required Avalon-MM transfers (up to one
write and one read) are completed.
Table 68. Instruction Execution Performance for Nios II/f Core 4byte/line data cache
Normal ALU instructions (e.g., add, cmplt)
Combinatorial custom instructions
Multicycle custom instructions
Branch (correctly predicted, taken)
Branch (correctly predicted, not taken)
Branch (mispredicted)
, , ,
trap break eret bret
instructions
, ,
call jmpi rdprs
, ,
jmp ret callr
rdctl
(without Avalon-MM transfer)
load
(with Avalon-MM transfer)
load
(without Avalon-MM transfer)
store
(with Avalon-MM transfer)
store
, (without Avalon-MM transfer)
flushd flushda
, (with Avalon-MM transfer)
flushd flushda
,
initd initda
,
flushi initi
Multiply
Nios II Processor Reference Guide
130
Instruction
, , , ; illegal and unimplemented
flushp wrctl wrprs
5. Nios II Core Implementation Details
, multiplies (if hardware multiply is
rdctl
Cycles
1
1
> 1
2
1
4
4 or 5
2
3
1
1
> 1
1
> 1
2
> 2
2
4
NII-PRG | 2018.04.18
Penalties
Late result
Pipeline flush
Pipeline flush
Late result
Late result
Late result
Late result
continued...