Pipeline Execution of Instruction Types
6-19
TMS320C67x Pipeline
All of the preceding cases deal with double-precision floating-point instruc-
tions or the MPYI or MPYID instructions except for the 4-cycle case. A 4-cycle
instruction consists of both single- and double-precision floating-point instruc-
tions. Therefore, the 4-cycle case is important for the following single-
precision floating-point instructions:
The .S and .L units share their long write port with the load port for the 32 most
significant bits of an LDDW load. Therefore, the LDDW instruction and the .S
or .L unit writing a long result cannot write to the same register file on the same
cycle. The LDDW writes to the register file on pipeline phase E5. Instructions
that use a long result and use the .L and .S unit write to the register file on pipe-
line phase E1. Therefore, the instruction with the long result must be sched-
uled later than four cycles following the LDDW instruction if both instructions
use the same side.