Freescale Semiconductor MCF51QE128RM manual Instruction Execution Timing, Timing Assumptions

ColdFire Core

7.3.4Instruction Execution Timing

This section presents processor instruction execution times in terms of processor-core clock cycles. The number of operand references for each instruction is enclosed in parentheses following the number of processor clock cycles. Each timing entry is presented as C(R/W) where:

•C is the number of processor clock cycles, including all applicable operand fetches and writes, and all internal core cycles required to complete the instruction execution.

•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.

7.3.4.1Timing 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 7-13.

Table 7-13. Misaligned Operand References

	address[1:0]	Size	Bus	Additional
			Operations	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,	3(2/0) if read
			Byte	2(0/2) if write
	10	Long	Word, Word	2(1/0) if read
				1(0/1) if write
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