Options with the data or
booldata flavors can have an arbitrary sequence of
characters as their data. In nearly all cases some restrictions have
to be imposed, for example the data should correspond to a number
within a certain range, or it should be one of a small number of
constants. The legal_values property can be used to impose such
constraints. The arguments to the property should be a CDL list
expression, see the Section called List Expressions in Chapter 3 for the
syntactic details. Common examples include:
The legal_values property can only be used for options with the
data or booldata flavors, since
it makes little sense to further constrain the legal values of a
boolean option. An option can have at most one legal_values
property.
Tip: If the first entry in a legal_values list expression is a negative
number, for example
legal_values -1 to 1 then this can
be misinterpreted as an option instead of as part of the expression.
Currently the legal_values property does not take any options, but
this may change in future. Option processing halts at the sequence
--, so the desired range can be expressed safely
using legal_values -- -1 to 1
Note: Architectural HAL packages should provide constants which can be used
in legal_values list expressions. For example it should be possible
to specify a numeric range such as
0 to CYGARC_MAXINT, rather than
hard-wiring numbers such as 0x7fffffff which may
not be valid on all targets. Current HAL packages do not define such
constants.
Note: The legal_values property is restricted mainly to numerical ranges
and simple enumerations, and cannot cope with more complicated data
items. Future versions of the configuration system will provide
additional data validation facilities, for example a
check_proc property which specifies a Tcl script
that can be used to perform the validation.
Example
cdl_option CYGNUM_LIBC_TIME_STD_DEFAULT_OFFSET {
display "Default Standard Time offset"
flavor data
legal_values -- -90000 to 90000
default_value -- 0
description "
This option controls the offset from UTC in
seconds when in local Standard Time. This
value can be positive or negative. It
can also be set at run time using the
cyg_libc_time_setzoneoffsets() function."
}
