Uninitialized .bss Variables in Simulation - Uninitialized .bss Variables in Simulation Description If your program reads the value of an uninitialized . bss variable during HDL simulation, and the BSP (system library) is compiled with the ModelSim only, no hardware support property enabled in Nios II IDE, a warning appears about unfiltered data being 'x' . This warning appears because when this property is enabled, the code that clears the . bss memory region is omitted to speed up HDL simulation so this memory region is uninitialized. The . bss region contains global and static local variables that are not initialized by the application so they default to a value of zero. When the Nios II processor reads uninitialized variables, it displays a warning and converts any of the bits of the uninitialized data to zero which correctly mimics the effect of the missing . bss clearing code. The Hardware Abstraction Layer (HAL) code that executes before and after main() might use . bss variables, so these warnings might appear even if your application does not use the . bss section. Custom Fields values: ['novalue'] Troubleshooting novalue True ['novalue'] ['FPGA Dev Tools Quartus II Software'] novalue 10.0 ['Programmable Logic Devices'] ['novalue'] ['novalue'] ['novalue']