Zilog ZUSBOPTS - Manual (Page 86)

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Zilog Developer Studio II – ZNEO™
User Manual
small fraction of applications benefit from deselecting the Use Register Variables check-
box.
The Use Register Variables checkbox interacts with the Limit Optimizations for Easier
Debugging checkbox on the C page (see the Limit Optimizations for Easier Debugging
section on page 52). When the Limit Optimizations for Easier Debugging checkbox is
selected, register variables are not used because they can cause confusion when debug-
ging. The
Use Register Variables checkbox 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 checkbox returns to the setting it had before the Limit Optimiza-
tions for Easier Debugging checkbox was selected.


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 Limit Optimi-
zations for Easier Debugging on page 52)
•
Deselect the Use Register Variables checkbox
•
Rewrite your code so that the variables in question become global rather than local

The other way in which register variables can lead to confusing behavior when debugging
is when the same register is used to store different variables or temporary results at differ-
ent 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 generate the required output. When the Generate Printfs Inline
checkbox is selected, the format 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 top-level routines to parse a format string are not linked into the
project, and only those lower level routines that are actually used are linked in, rather than
every routine that could be used by a call to
printf . The code size of each routine that
calls printf() or sprintf() is slightly larger than if the Generate Printfs Inline
checkbox is deselected, but this is more than offset by the significant reduction in the size
of library functions that are linked to your application.
To reduce overall code size by selecting this checkbox, the following conditions are neces-
sary:
Notes: