Observing Memory Transactions

16.1 Observing Memory Transactions

Memory-spaces provide a memory hierarchy interface for observing and modifying memory transactions passing through them. This interface is in fact composed of two different interfaces acting at different phases of a memory transaction execution:

The timing-model interface provides access to a transaction before it has been executed (i.e., it has just arrived at the memory-space).
To connect an object to the timing model interface, just set the timing_model attribute of the corresponding memory-space with the value of the object you want to connect:
```
simics> @conf.phys_mem0.timing_model = conf.listening_object
```
The timing model interface can also be used to change the timing and the execution of a memory transaction, as well as to modify the value of a store going to memory. This is described in more detail in section 16.2 and in the Simics Programming Guide.

The snoop-memory interface provides access to a transaction after it has been executed.
Connecting an object to the snoop memory interface is done in the same way as for the timing model interface:
```
simics> @conf.phys_mem0.snoop_device = conf.listening_object
```
The trace module, for example, automatically connects itself (or rather one of its objects) to this interface when a trace is started. The advantage of using this interface is that the value of load operations is accessible, since the operation has already been performed.
The snoop memory interface can also be used to modify the value of a load operation. This is described in more detail in the Simics Programming Guide.

Note: Both interfaces can be used simultaneously, even by the same object. This property is used by the trace module, which is in fact connected both to the timing-model and the snoop-memory interfaces. The reason for this double connection is explained later in this chapter.

Previous - Up - Next