2.8.5. Configuring the map memory model

You can configure the map memory model to model several different types of memory controller, by editing its entry in the peripherals.ami file:


{ Default_Mapfile=Mapfile
AMBABusCounts=False
;SpotISCyles=True|False
SpotISCyles=True
;ISTiming=Late|Early|Speculative
ISTiming=Late
}

Counting AMBA™ decode cycles

You can configure the model to insert an extra decode cycle for every nonsequential access from the processor. This models the decode cycle seen on some AMBA bus systems. Enable this by setting AMBABusCounts=True in peripherals.ami.

Merged I-S cycles

All ARM processors, particularly cached processors, can perform a nonsequential access as a pair of idle and sequential cycles, known as merged I-S cycles. By default, the model treats these cycles as a nonsequential access, inserting wait states on the S-cycle to lengthen it for the nonsequential access.

You can disable this by setting SpotISCycles=False in peripherals.ami. However, this is likely to result in exaggerated performance figures, particularly when modeling cached ARM processors.

The model can simulate merged I-S cycles using one of three strategies:

Speculative

This models a system where the memory controller hardware speculatively decodes all addresses on idle cycles. The controller can use both the I- and S-cycles to perform the access. This results in one fewer wait state.

Early

This starts the decode when the ARM declares that the next cycle is going to be an S-cycle, that is, half-way through the I-cycle. This can sometimes result in one fewer wait states. (Whether or not there are fewer wait states depends on the cycle time and the nonsequential access time for that region of memory.)

This is the default setting. You can change this by setting ISTiming=Spec or ISTiming=Late in peripherals.ami.

Late

This does not start the decode until the S-cycle. In effect all S-cycles that follow an I-cycle are treated as if they are N-cycles.

See ARMulator cycle types for details of merged I-S cycles.

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