Urgency : Low
General Description :
When attempting to add a DC load to an output in XPower, I receive a warning message similar to the following:
"WARNING:Power:303 - I/O <dout_OBUF> cannot provide <12.0mA> DC load because it is configured with drive strength <4.0mA>, using configured drive strength."
This issue has been fixed in ISE version 7.1i.
Version 6.3i or earlier:
There is a bug in XPower where the maximum output drive strength is assumed to be 4mA, regardless of the actual output drive strength assigned in the project. Whenever a value greater than 4mA is entered, the warning message is produced and the value is automatically adjusted to 4mA.
The actual power consumed is estimated to be 50% of the value entered in the DC Load section. For example, if 4mA were entered, the estimated power consumption for the load is 2mA because it is assumed that the output is 50/50 duty cycle so the load will be present only half of the time.
To work around this bug, manually estimate the power.
Simply divide the DC load power by 2 to determine the additional current, then sum this with all other DC loads and multiply by the VCCO value to obtain power for the DC load. This can then be added on to the power given in the XPower report.