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<a href="#" onmousedown="showPopup(this, 'popup00579');"><img src="seealsolink.png" border="0" alt="" title=""></a> SystemVerilog 3.1a语言参考手册</div>
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30.8.4.1 Traversing value changes of objects</div>
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After getting a traverse vpiHandle, the application can do a forward or backward walk or jump traversal by using vpi_goto() on a vpiTrvsObj object type with the new traverse properties. </p>
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Here is a sample code segment for the complete process from handle creation to traversal. </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code01047"><pre class="Element12">p_vpi_extension reader_p; /* Pointer to VPI reader extension structure */
vpiHandle instanceHandle; /* Some scope object is inside */
vpiHandle var_handle; /* Object handle */
vpiHandle vc_trvs_hdl; /* Traverse handle */
vpiHandle itr;
p_vpi_value value_p; /* Value storage */
p_vpi_time time_p; /* Time storage */
PLI_INT32 code; /* return code */
...
/* Initialize the read interface: Access data from memory */
/* NOTE: Use built-in VPI (e.g. that of simulator application is running
under) */
reader_p = vpi_load_extension(NULL, NULL, vpiAccessLimitedInteractive);
if (reader_p == NULL) ... ; /* Not successful */
/* Initialize the load: Access data from simulator) memory, for scope
instanceHandle and its subscopes */
/* NOTE: Call marks access for all the objects in the scope */
vpi_load_init(NULL, instanceHandle, 0);
itr = vpi_iterate(vpiVariables, instanceHandle);
while (var_handle = vpi_scan(itr)) {
/* Demo how to force the load, this part can be skipped in general */
if (vpi_get(vpiIsLoaded, var_handle) == 0) { /* not loaded*/
/* Load data: object-based load, one by one */
if (!vpi_load(var_handle)); /* Data not found ! */
break;
}
/*-- End of Demo how to force the load, this part can be skipped in general */
/* Create a traverse handle for read queries */
vc_trvs_hdl = vpi_handle(vpiTrvsObj, var_handle);
/* Go to minimum time */
vc_trvs_hdl = vpi_goto(vpiMinTime, vc_trvs_hdl, NULL, NULL);
/* Get info at the min time */
time_p->type = vpiSimTime;
vpi_get_time(vc_trvs_hdl, time_p); /* Minimum time */
vpi_printf(...);
vpi_get_value(vc_trvs_hdl, value_p); /* Value */
vpi_printf(...);
if (vpi_get(vpiHasDataVC, vc_trvs_hdl)) { /* Have any VCs ? */
for (;;) { /* All the elements in time */
vc_trvs_hdl = vpi_goto(vpiNextVC, vc_trvs_hdl, NULL, &code);
if (!code) {
/* failure (e.g. already at MaxTime or no more VCs) */
break; /* cannot go further */
}
/* Get Max time: Set bits of s_vpi_time type field */
/* time_p->type = vpiMaxTime & vpiSimTime; */
/* vpi_get_time(vc_trvs_hdl, time_p); */
time_p->type = vpiSimTime;
vpi_get_time(vc_trvs_hdl, time_p); /* Time of VC */
vpi_get_value(vc_trvs_hdl, value_p); /* VC data */
}
}
}
/* free handles */
vpi_free_object(...);</pre></div></div>
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The code segment above declares an interactive access scheme, where only a limited history of values is provided by the tool (e.g. simulator). It then creates a Value Change (VC) traverse handle associated with an object whose handle is represented by var_handle but only after vpi_load_init() is called. It then creates a traverse handle, vc_trvs_hdl. With this traverse handle, it first calls vpi_goto() to move to the minimum time where the value has changed. It moves the handle (internal index) to that time by calling vpi_goto() with a vpiMinTime argument. It then repeatedly calls vpi_goto() with a vpiNextVC to move the internal index forward repeatedly until there is no value change left. vpi_get_time() gets the actual time where this VC is, and data is obtained by vpi_get_value(). The application can also choose to call vpi_goto() with a time_p argument to automatically get the VC time instead of calling vpi_get_time() separately to get this information. </p>
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The traverse and collection handles can be freed when they are no longer needed using vpi_free_object().</p></div>
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