Zilog Z8F0130 - Manual (Page 108)

Using the Integrated Development Environment UM013037-1212
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Zilog Developer Studio II – Z8 Encore!
User Manual
rule. For example, in an application that contains 50 functions, this drop-down list box
might make 2 functions larger and the other 48 functions smaller. Also, if those two func-
tions run slower with the drop-down list box enabled but the others run faster, then
whether the overall program speed is improved or worsened depends on how much time
the application spends in each function.
Because the effect of applying this drop-down list box must be evaluated across an appli-
cation as a whole, user experimentation is required to test this for an individual applica-
tion. Only a small fraction of applications benefit from setting the
Use Register
Variables drop-down list box to Off .
This drop-down list box interacts with the Limit Optimizations for Easier Debugging
checkbox on the C page (see the Limit Optimizations for Easier Debugging section on page
77). When the Limit Optimizations for Easier Debugging checkbox is selected, register
variables are not used because they can cause confusion when debugging. The Use Regis-
ter Variables drop-down list box is disabled (grayed out) when the Limit Optimizations
for Easier Debugging checkbox is selected. If the Limit Optimizations for Easier
Debugging checkbox is later deselected (even in a later ZDS II session), the Use Register
Variables drop-down list box returns to the setting it had before the Limit Optimizations
for Easier Debugging checkbox was selected.
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Using register variables can complicate debugging in at least two ways. One way is that
register variables are more likely to be optimized away by the compiler. If variables you
want to observe while debugging are being optimized away, you can usually prevent this
by any of the following actions:
•
Select the Limit Optimizations for Easier Debugging checkbox (see the Limit Opti-
mizations for Easier Debugging section on page 77).
•
Set the Use Register Variables drop-down list box to Off .
•
Rewrite your code so that the variables in question become global rather than local.
The other way that register variables can lead to confusing behavior when debugging is
that the same register can be used for different variables or temporary results at different
times in the execution of your code. Because the debugger is not always aware of these
multiple uses, sometimes a value for a register variable might be shown in the
Watch win-
dow that is not actually related to that variable at all.
Generate Printfs Inline
Normally, a call to printf() or sprintf() parses the format string at run time to gener-
ate the required output. When the Generate Printfs Inline checkbox is selected, the for-
mat string is parsed at compile time, and direct inline calls to the lower level helper
functions are generated. This results in significantly smaller overall code size because the
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