Echelon Neuron C - Manual (Page 213)

Neuron C Programmer’s Guide 201
can consider removing the self-identification data. You can do this by specifying
the following compiler directive:
#pragma disable_snvt_si
Remove Network Variable Names if Not Needed
The Neuron C compiler places information about the names of the network
variables in the device’s program space when the compiler directive #pragma
enable_sd_nv_names appears in the program. This data consumes EEPROM.
You can remove the directive to regain one byte of EEPROM space for each
character in a network variable’s name, plus one byte for each network variable.
When the device is installed, if there is no further information available about
the network variable names, the network tool automatically assigns generic
names such as "NVI1", "NVO7", and so on.
To assist the network integrator and allow the use of intuitive, self-explanatory
names of the network variables as opposed to the generic, automatically
generated ones, provide the external interface files along with your device. The
network management software extracts the names for the network variables
from the files (.XIF or .XFB extensions), without the names consuming code space
in your device.
Declare Constant Data Properly
Use of the const or eeprom keyword in a declaration of constant data is very
important, because, without either of these keywords, the compiler assumes the
data is placed in RAM and thus the data needs to be initialized at runtime (each
time the application program is reset). This process can be very expensive in
terms of code space, it unnecessarily consumes RAM memory, and it also
unnecessarily lengthens the time it takes the application to complete its reset
processing.
Consider the following example. This example shows a poorly declared data table
of four bytes in length. Unfortunately, because this declaration does not use the
const keyword, the compiler places it in RAM, and it must therefore be initialized
each time the application processor resets. The executable code fragment to
initialize the array is an additional 9 bytes, and another four bytes are placed in
code space containing the initial values for the table.
Furthermore, use of RAM for the data table means that there is a chance it could
accidentally get modified by an unintentional programming error.
Example of poor declaration:
int lookup_table[4] = {1, 4, 7, 13};
The proper declaration of the data table only consumes four bytes of read-only
memory (code space) for the data values themselves.
Example of proper declaration:
const int lookup_table[4] = {1, 4, 7, 13};