Power Rail Creation and Management - 2021.2 English

Vivado Design Suite User Guide: Power Analysis and Optimization (UG907)

Document ID
Release Date
2021.2 English
A rail or power rail refers to a group of supplies or power rails. In this section, a supply or power supply refers to an individual device power supply such as Vccint and Vccram. An auxiliary power supply can have voltage regulators that are fed by multiple sources in different phases. To handle this, user may need to add a power rail in multiple groups to account for voltage sources drawing current from different phases. Power rail definitions, the number of phases for a power rail as well as phase distribution on a rail and their current budgets are typically supplied with the target board files. Xilinx supports Tcl commands to overwrite board data or to create rail definitions, update phase information, and current budgets. Following are some useful commands:
Creates a new power rail.
create_power_rail <power rail name> -power_sources  {supply1, supply2 ,..}
create_power_rail <power rail name> -power_sources {supply1, supply2 ,..} -num_phases <number of phases>

create_power_rail <power rail name> -power_sources {supply1, supply2 ,..} -phased_power_source {<power rail name with phase info>  <num_phase>}
Deletes an existing power rail.
delete_power_rail <power rail name>
Add power sources to an existing power rail.
add_to_power_rail  <power rail name> -power_sources {supply1, supply2, ..}
add_to_power_rail <power rail name> -power_sources {supply1, supply2, ..} -phased_power_source { <power_rail_with_phase_info> <num_phases> }
Removes power sources from a power rail.
remove_from_power_rail  <power rail name> -power_sources {supply1, supply2, ..}

When defined, the supply current budget can be specified for the Power Rails along with the Rail voltage. The power budget of the Rail is the supply current budget multiplied by the Rail voltage. Use the following command to specify the power and supply current budget:

set_operating_conditions -supply_current_budget {<supply rail name> <current budget in Amp>} -voltage {<supply rail name> <voltage>}

Tip: Power rail reporting is not fully supported in the Report Power GUI, to view the complete results, ensure to generate a .txt output file.

Report Power compares the current on each Power Rail against their current budget and indicates positive and negative margin in the power text report as discussed in the previous section. The following figure shows a power text report with Power Rails and their budgets.

Figure 1. Power Text Report
Note: As of 2020.2 Vivado release, only U50 board files support Power meta-data such as Power Rail definition and their current budgets. Additional boards will support power rails in future releases.