Cdp; Figure 8-6 Latecanceled Cdp - ARM ARM926EJ-S Technical Reference Manual

Coprocessor Interface
8.4

CDP

8-8
instructions usually execute in a single cycle. Like all the previous cycles,
CDP
nCPMREQ is driven LOW to signal when an instruction is entering the Decode and
then the Execute stage of the pipeline. If the instruction is to be executed then the
CPPASS signal is driven HIGH during Execute. If the coprocessor can execute the
instruction immediately it drives CHSDE[1:0] with LAST. If the instruction requires a
busy-wait cycle, then the coprocessor drives CHSDE[1:0] with WAIT and then
CHSEX[1:0] with LAST. Figure 8-6 shows a CDP that is canceled due to the previous
instruction causing a Data Abort.
Coprocessor pipeline
CLK
CPINSTR[31:0]
nCPMREQ
CPPASS
CPLATECANCEL
CHSDE[1:0]
CHSEX[1:0]
The CDP instruction enters the Execute stage of the pipeline and is signaled to execute
by CPPASS. In the following phase CPLATECANCEL is asserted. This causes the
coprocessor to terminate execution of the CDP instruction and for it to cause no state
changes to the coprocessor.
Note
CPLATECANCEL can be asserted during the Memory cycle or during the Execute
cycle. The coprocessor must be able to handle instruction aborts during these two
stages.
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Fetch Decode Execute
CPRT
LAST
Ignored
Instruction
Memory
aborted

Figure 8-6 Latecanceled CDP

ARM DDI0198D