Mips Technologies R4000 - Resource Scheduling Rules

Chapter 6
182 MIPS R4000 Microprocessor User's Manual
Resource Scheduling Rules
The FPU Resource Scheduler issues instructions while adhering to the
rules described below. These scheduling rules optimize op unit
executions; if the rules are not followed, the hardware interlocks to
guarantee correct operation.
DIV.[S,D] can start only when all of the following conditions are met in
the RF stage:
• The divider is either idle, or in its second-to-last execution cycle.
• The adder is either idle, or in its second-to-last execution cycle.
• The multiplier is either idle, or in its second-to-last execution
cycle.
Idle means an operation unit—adder, multiplier or divider—is either not
processing any instruction, or is currently in its last execution cycle
completing an instruction.