write access
2-cycle external bus
Pipeline Conflicts
8-16
Example 8–11. Busy External Port

STF R0,@DMA1

LDF @DMA2,R0

Pipeline Operation
PC Fetch Decode Read Execute
nSTF —
n+1 LDF STF
n+2 W LDF STF
n+2 W LDF (nop) STF
n+2 W LDF (nop) (nop)
n+3 X W LDF (nop)
n+4 YXWLDF
Note: W, X, Y = Instruction representations

The second type of hold-everything conflict involves multicycle data reads.

The read has begun and continues until completed. In Example 8–12, the LDF

is performed from an external memory that requires several cycles to access.