Xilinx virtex-5 fpga

314 www.xilinx.com Virtex-5 FPGA User Guide
UG190 (v5.0) June 19, 2009
Chapter 6: SelectIO Resources
SSO Allowance = SF1 × SF2 × SF3 × 100%
=0.909× 0.917 × 0.905 × 100%
= 75.4%
Weighted Average Calculation of SSO
This section describes the SSO calculation where the SSO contributions of all I/O in a bank
are combined into a single figure.
SSO of an individual bank is calculated by summing the SSO contributions of the
individual I/O standards in the bank. The SSO contribution is the percentage of full
utilization of any one I/O standard in any one bank. For drivers of each I/O standard, the
calculation follows:
SSO Contribution (I/ O group n) = (quantity of drivers)/(Bank SSO limit)
For a bank with drivers of multiple I/O standards, the SSO calculation is:
A sample SSO calculation follows. The system parameters used are:
Device: XC5VLX50 FF1153
Bank: 11
I/O Standards, Quantities:
SSTL2_II, 12
LVCMOS25_24 Fast, 6
LVCMOS25_6 Fast, 19
First, SSO limits for each I/O standard are obtained from Table 6-40:
The SSO contribution of each I/O standard is calculated as:
SSO Contribution = (quantity of drivers)/(Bank SSO limit)
SSO Contribution (1) = 12/40 = 30%
SSO Contribution (2) = 6/30 = 20%
SSO Contribution (3) = 19/40 = 48%
Finally, the bank SSO is calculated:
Bank 1 SSO = SSO contribution (1) + SSO contribution (2) + SSO Contribution (3)
= 30% + 20% + 48% = 98%
I/O Group I/O Standard SSO Limit (Drivers per Bank)
1 SSTL2_II 40
2 LVCMOS25_24 Fast 30
3 LVCMOS25_6 Fast 40
Bank SSO SSO Contribution n()
1 to n()
∑
=