Intel® Hyperflex™ Architecture High-Performance Design Handbook

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ID 683353
Date 10/04/2021
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2.2.7.3.2. Intel® Quartus® Prime Settings for Initial Conditions

You can use the following Intel® Quartus® Prime settings that have an impact on initial conditions.

Power-Up Don't Care Logic Option

You can enable the retiming of more registers by making sure that the Power-Up Don't Care Logic option (ALLOW_POWER_UP_DONT_CARE) is On. This option specifies that registers without explicit initial conditions in the RTL power-up to don't care. This option is set to On by default.

set_global_assignment -name ALLOW_POWER_UP_DONT_CARE ON

Any initial conditions that you specify in the RTL, or any initial conditions that are implied (because of language specifications or FSM initial states) still apply when using ALLOW_POWER_UP_DONT_CARE.

Ignoring Initial Conditions

Because of factors such as language specifications and conservative synthesis on structures such as state machines, it is possible for initial conditions to appear on certain registers, even though you expect no initial conditions to appear. Such initial conditions can potentially cause performance limitations. If you verify that removing such initial conditions is functionally correct, you can specify the following .qsf assignment to remove those initial conditions:

set_instance_assignment -name IGNORE_REGISTER_POWER_UP_INITIALIZATION ON \
     -to <instance name>

The Synthesis report identifies registers affected by IGNORE_REGISTER_POWER_UP_INITIALIZATION in the "Registers with Power-Up Settings Ignored" report.

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