Floating-Point IP Cores User Guide

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ID 683750
Date 9/13/2021
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10.5.1. ALTFP_LOG Design Example: Understanding the Simulation Results

The simulation waveform in this design example is not shown in its entirety. Run the design example files in the ModelSim* - Intel® FPGA Edition software to see the complete simulation waveforms.

These figures show the expected simulation results in the ModelSim* - Intel® FPGA Edition software.

Figure 31. ALTFP_LOG Simulation Waveform (Input Data)
Figure 32. ALTFP_LOG Simulation Waveform (Output Data)

This design example includes the input of special cases to show the exception handling of the IP core, such as the smallest valid input and the input value of “1”.

In this example, the output delay is set to 21 clock cycles. Therefore, the result is only shown at the output port after the 21st clock cycle at 102.5 ns.

Table 61.  Summary of Input Values and Corresponding OutputsThis table lists the inputs and corresponding outputs obtained from the simulation in the waveforms.
Time Event
0 ns, start-up data[] value: 0000 0000h

Output value: An undefined value is seen on the result[] port, which is ignored. All values seen on the output port before the 21st clock cycle are merely due to the behavior of the system during start-up and should be disregarded.

102.5 ns Output value: FF80 0000h

The natural logarithm of zero is negative infinity.

5 ns data[] value: 8000 0000h

This is a negative number.

107.5 ns Output value: FFC0 0000h

Exception handling ports: nan asserts

The natural logarithm of a negative value is invalid. Therefore, the output produced is a NaN.

30 ns data[] value: 0040 0000h

The is a denormal value.

132.5 ns Output value: FF80 0000h

As denormal numbers are not supported, the input is forced to zero before going through the logarithm function. The natural logarithm of zero is negative infinity.

45 ns data[] value: 0080 0000h

This is the smallest valid input. All the input bits are 0 except the LSB of the exponent field.

147.5 ns Output value: C2AE AC50h
60 ns data[] value: 3F80 0000h

The input value 3F80 0000h is equivalent to the actual value, 
1.0 × 20 = 1.

152.5 ns Output value: 0000 0000h

Exception handling ports: zero asserts

Since In 1 results in zero, it produces an output of zero.

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