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Honored Contributor
Honored ContributorModelsim simulation problem: altfp_mult floating point multiplier Megafunction
Hallo everybody,
i have a problem when doing a functional simulation on Altera altfp_mult Megafunction: I configured the Megafunction to multiply two 32 bit floats with 5 clock cycles latency, and Modelsim shows me an unknown state of bits 30-23 after 2 clock cycles. However, the result after 5 clock cycles is correct. This behavior only occures with the first multiplication, if a change inputs after 5 clock cylces, i will get the right result without this strange behavior. The big problem ist that i want to cascade more multipliers and floating point adders for a PID controller, and if the first multiplication is wrong, the whole simulation will fail. I have implemented the multiplier on my Cyclon III Starter Kit and checkt the multiplier with Signal Tap. In rela life i could not monitor any strange behavior, so a guess that it is a simulation error, or that something is wrong with my simulation settings. Please see the attached picture of the simulation. I created the Megafunction with the Quartus II MegaWizard. My Modelsim projects include only the altfp_mult vhdl file and one testbench file to generate the clock an the stimuli. I will post this files and project settings if necessary. data_in_a and data_in_b are the inputs of the multiplier, res is the output. Signal clk is the clock signal. I hard-wired clk_en to '1' and aclr to '0'. Signals nan, ov, uv and zero a the flags of the multiplier. Can anybody tell me why this thing happens, and how can i avoid this behavior? Thanks in advance, magixD
