User`s guide

Upgrading from an Earlier Release
3-13
Upgrading from an Earlier Release
This section discusses upgrade issues in moving from Simulink 4.0 to Simulink
4.1.
See the Release Notes for Release 12 for upgrade issues involved in moving from
Simulink 3.0 (Release 11.0) to Simulink 4.1.
Running Simulink 4.1 Models in Simulink 4.0
Simulink 4.0 can run models created or saved by Simulink 4.1 as long as the
models do not use features introduced in the new version, including new block
types and block parameters. In particular, you should not attempt to use
Simulink 4.0 to simulate or even open models that use the new Simulink
control flow blocks. Opening such models cause Simulink 4.0 to crash.
Simulink Block Library Reorganization
The Simulink Block Library contains a new Subsystems sublibrary. The new
library contains most of the new control flow blocks as well as subsystem and
subsystem-related blocks that used to reside in the Signals & Systems library.
The subsystems in the new library each contain the minimum set of blocks
needed to create a functioning subsystem, e.g., an input port and an output
port.
Direct Feedthrough Compensation Deprecated
If an S-function needs the current value of its input to compute its output, it
must set its direct feedthrough flag to true. Previously, if a direct feedthrough
S-function failed to do this, Simulink tried to provide a valid signal to the
S-function’s
mdlOutput (M-file flag=3) or mdlGetTimeOfNextVarHit (M-file
flag=4) methods. This special compensation mode for S-functions was flawed.
For this reason, the current version deprecates the mode, though making it
available as an option. In this version, by default, if an S-function sets its direct
feedthrough flag to false during initialization, Simulink sets the S-function’s
input signal to
NULL (or a NaN signal for M-file S-functions) during the
mdlOutput or mdlGetTimeOfNextVarHit methods. Thus, in this version, models
with S-function(s) may produce segmentation violations. See
matlabroot/
simulink/src/sfuntmpl_directfeed.txt
for more information.