Xilinx devices have dedicated block RAM resources. To accurately set Block RAM parameters in XPE, a good understanding of device resources and configuration possibilities is recommended. If implementation details for the block RAM are known, follow the guidelines described in Setting Block RAM Mode for Improved Accuracy. Otherwise, refer to Preliminary Block RAM Estimates.
Note: Distributed RAM/ROM and SRL usage should be specified in Using an I/O Sheet.To enter information on the Block RAM sheet, you can use the XPE Memory Generator wizard, which appears when you click the Add Memory button on the Block RAM sheet. The XPE Memory Generator wizard provides a simplified method of adding rows to the Block RAM sheet. For information about using this wizard, see Memory Generator Wizard and the Block RAM Sheet (Block Memory).
Following are details about columns in the Block RAM sheet:
- Enable Rate column
- Use the Enable Rate to specify the percentage of time each of the block RAM ports are enabled for reading and/or writing. To save power, the RAM enable can be driven Low on clock cycles when the block RAM is not used in the design. Block RAM Enable Rate, together with Clock rate, are important parameters that must be considered for power optimization.
- Write Rate column
- The Write Rate represents the percentage of time that each block RAM port performs write operations. The read rate is understood to be 100% – write rate. This is not relative to Enable Rate. For example, if the Enable Rate is 25% and write operation can be half of the time, then Write Rate is 12.5% of total time period.
- Signal Rate column (Read only)
- Defines the number of millions of transitions per second for the considered
block RAM output port. This is a read-only column which takes into account port
enable rates and a weighted average of the port widths.
The following figure illustrates the effect of block RAM configuration modes and bit widths on power estimates.
Figure 1. Block RAM Sheet - Effect of Block RAM Configuration Modes and Bit Widths on Power Estimates (7 Series Devices)