mcf5282 Freescale Semiconductor, Inc, mcf5282 Datasheet - Page 91

• Manufacturer Part Number: mcf5282
• Manufacturer: Freescale Semiconductor, Inc

3.3.3
The instruction execution times for the EMAC can be found in
Execution
The EMAC execution pipeline overlaps the AGEX stage of the OEP (the first stage of the EMAC pipeline
is the last stage of the basic OEP). EMAC units are designed for sustained, fully-pipelined operation on
accumulator load, copy, and multiply-accumulate instructions. However, instructions that store contents
of the multiply-accumulate programming model can generate OEP stalls that expose the EMAC execution
pipeline depth:
The MOVE.L instruction that stores the accumulator to an integer register (Rz) stalls until the
program-visible copy of the accumulator is available.
In
minus 1. The minus 1 factor is needed because the OEP and EMAC pipelines overlap by a cycle, the
AGEX stage. As the store-accumulator instruction reaches the AGEX stage where the operation is
performed, the recently updated accumulator 0 value is available.
Freescale Semiconductor
Load Accumulator
Extensions 23
Store Accumulator
Extensions 01
Store Accumulator
Extensions 23
Figure
mac.w
move.l
Command
3-9, the OEP stalls the store-accumulator instruction for three cycles: the EMAC pipleline depth
Times”.
EMAC Instruction Execution Times
Ry, Rx, Acc0
Acc0, Rz
AGEX
EMAC EX1
EMAC EX3
EMAC EX4
Accumulator 0
DSOC
EMAC EX2
move.l {Ry,#imm},ACCext23 Loads the accumulator 2,3 extension bytes with a 32-bit
move.l ACCext01,Rx
move.l ACCext23,Rx
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3
Table 3-8. EMAC Instruction Summary (continued)
Figure 3-9. EMAC-Specific OEP Sequence Stall
Mnemonic
mac
mac
mac
regBusy stall
Three-cycle
move
mac
operand
Writes the contents of accumulator 0,1 extension bytes into a
CPU register
Writes the contents of accumulator 2,3 extension bytes into a
CPU register
Figure 3-9
old
mac
Section 2.3.5.6, “EMAC Instruction
shows EMAC timing.
move
mac
Enhanced Multiply-Accumulate Unit (EMAC)
Description
move
move
new
3-13