Motorola ColdFire MCF5281 - Manual (Page 72)

ColdFire Core
2-26 Freescale Semiconductor
• R/W is the number of operand reads (R) and writes (W) required by the instruction. An operation
performing a read-modify-write function is denoted as (1/1).
This section includes the assumptions concerning the timing values and the execution time details.
2.3.5.1 Timing Assumptions
For the timing data presented in this section, these assumptions apply:
1. The OEP is loaded with the opword and all required extension words at the beginning of each
instruction execution. This implies that the OEP does not wait for the IFP to supply opwords and/or
extension words.
2. The OEP does not experience any sequence-related pipeline stalls. The most common example of
stall involves consecutive store operations, excluding the MOVEM instruction. For all STORE
operations (except MOVEM), certain hardware resources within the processor are marked as busy
for two clock cycles after the final decode and select/operand fetch cycle (DSOC) of the store
instruction. If a subsequent STORE instruction is encountered within this 2-cycle window, it is
stalled until the resource again becomes available. Thus, the maximum pipeline stall involving
consecutive STORE operations is two cycles. The MOVEM instruction uses a different set of
resources and this stall does not apply.
3. The OEP completes all memory accesses without any stall conditions caused by the memory itself.
Thus, the timing details provided in this section assume that an infinite zero-wait state memory is
attached to the processor core.
4. All operand data accesses are aligned on the same byte boundary as the operand size; for example,
16-bit operands aligned on 0-modulo-2 addresses, 32-bit operands aligned on 0-modulo-4
addresses.
The processor core decomposes misaligned operand references into a series of aligned accesses as
shown in
Table 2-11 .
2.3.5.2 MOVE Instruction Execution Times
Table 2-12 lists execution times for MOVE.{B,W} instructions; Table 2-13 lists timings for MOVE.L.
NOTE
For all tables in this section, the execution time of any instruction using the
PC-relative effective addressing modes is the same for the comparable
An-relative mode.
Table 2-11. Misaligned Operand References
address[1:0] Size
Bus
Operations
Additional
C(R/W)
01 or 11 Word Byte, Byte 2(1/0) if read
1(0/1) if write
01 or 11 Long Byte, Word,
Byte
3(2/0) if read
2(0/2) if write
10 Long Word, Word 2(1/0) if read
1(0/1) if write
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3