eldo_user

• .OPTION PRINT_OPTION=0 (in the Eldo Reference Manual)
Specifying Simulation Output
Limiting the Size of Transient Output Files
Disables the printing of the option summary in the ASCII output .chi file.
Limiting the Size of Transient Output Files
At least three options are available in Eldo to limit the size of the output files for transient
simulation: option OUT_STEP, option OUT_RESOL, and option INTERP.
Of course, the many options related to the accuracy settings do generally have an impact upon
the number of computed points and thus upon the size of the output files, but this is only
qualitative and indirect. There is no way to quantitatively relate, say the eps or the reltol
specification, to the final size of the output files—this all depends on the circuit. In contrast, the
options discussed in this section enable controlling the amount of data in a predictable way (the
OUT_RESOL option only sets a maximum size, whereas OUT_STEP and INTERP enable
exact predictions). These options may have a considerable impact on the overall simulation
speed, so it is important to define exactly what has to be achieved.
• .OPTION OUT_STEP=val (in the Eldo Reference Manual)
The .OPTION OUT_STEP=val command forces a timepoint at each multiple of val, and
only these timepoints are stored in the binary output files. These timepoints are forced,
that is, they come in addition to the normal timepoints picked by the simulator. When
using this option, the timepoints are forced, that is, they are computed even if they are
not required from an accuracy point of view. One of the applications of the OUT_STEP
option is for FFT computations. In this case, it is frequent that the user wants to have
exact, computed points, at regularly spaced timepoints, to minimize the interpolation
artifacts when computing an FFT. However the OUT_STEP option is also a way to
control the size of the output files, even if no FFT is scheduled. If not chosen properly, a
possible risk of the OUT_STEP option is to slowdown the simulation unnecessarily, by
forcing Eldo to compute more points than needed. This is particularly true if they are
long periods of time with little or no activity in the simulation. Forcing a short out_step
will force many useless timepoints during these periods, whereas Eldo would normally
accelerate and compute fewer timepoints. This option is however preferred by some
users because the output waveforms ultimately contain only computed points, without
interpolation.
• .OPTION OUT_RESOL=resolution (in the Eldo Reference Manual)
Another option used to reduce the size of the output file is the OUT_RESOL option.
With this option, the user can specify the smallest resolution of the output file.
Computed data is then dumped only if the current time is greater than the previously
written timepoint, augmented by the resolution. For example if OUT_RESOL is set to
1ns, and the simulator has written data at time t=24.65ns, all timepoints computed until
t=25.65ns will not be dumped. The first timepoint after t=25.65ns will be dumped. This
could be t=25.76ns for example, or t=27ns if the simulator can accelerate in this period
of time. No timepoints are forced other than those naturally picked by the simulator.
Eldo® User's Manual, 15.3 353