An issue has been discovered in Quartus® II software versions 4.1 and 4.1 service pack 1 that can cause a small percentage of designs that use counters to generate incorrect logic within Stratix®, Stratix GX, Cyclone™, MAX® II, and HardCopy® Stratix device families. When this issue occurs, designs that target these devices will function differently in the device than what the user intended. This issue occurs in the Quartus II software across all OS platforms and in the free Quartus II Web Edition software; Quartus II software versions 4.0 and earlier are not affected by this issue. This page is intended to inform you about the issue and to provide instructions to fix it. Altera has corrected this issue, and patches are now available for installation.
- How Can This Issue Affect My Design?
- How Can I Detect if This Issue is Affecting My Current Design?
- How Do I Fix This Issue?
All platforms of Quartus II software version 4.1 and 4.1 service pack 1, including the free Web Edition, have an issue in the counter implementation such that when synchronous clear and asynchronous set signals are used, the synchronous clear signal logic is not generated. This issue occurs only when all three of the following conditions occur:
- The design targets a Stratix, Stratix GX, Cyclone, MAX II, or HardCopy Stratix device.
- The counter uses both synchronous clear and asynchronous set signals.
- The counter is explicitly instantiated with the lpm_counter megafunction in Quartus II integrated synthesis or any third-party synthesis software or in a schematic file, or is inferred by Quartus II integrated synthesis.
Note: Third-party synthesis tools do not infer the lpm_counter megafunction and users of these tools will not be affected by this issue unless the user explicitly instantiates the lpm_counter megafunction in their VHDL or Verilog code.
You can discover this issue within gate-level simulation. Your testbench would need to simulate the synchronous clear behavior.
How Do I Fix This Issue?
Patches are now available to fix this issue. For each Quartus II software platform you have two options. You can download a patch file specific to your Quartus II software that fixes only this counter issue, or you can download a service pack 2 release that includes service pack 1 and the fix for this counter issue. This fix disables the "Generate a Clearbox body (for EDA Tools only)" feature for the lpm_counter megafunction, this feature will be supported in the next release of the Quartus II software.
Note: After installing a patch, if any lpm_counter megafunctions are included in your existing design, rerun the lpm_counter MegaWizard function to make sure the "Generate a Clearbox body (for EDA tools only)" option is turned off. You must then re-compile the design to complete the fix. Additional work-around information is available in the Altera solutions database.
Please use the following tables to download the correct software patch for your specific installation. Table 1 is for subscription customers and Table 2 is for Web Edition users.