Echelon Neuron C - Manual (Page 214)

202 Memory Management
Use Efficient Constant Values
In the Neuron Chip and Smart Transceiver CPU architecture, constants in the
range of 0 to 7 can be used more efficiently than larger 8-bit constants.
Instructions that use these constant values are smaller and faster. Therefore,
when choosing a sequence of constant values, normalize the sequence to begin
with 0. An enumerated type (an enum) is, by default, normalized with zero in
this manner.
Also, because the Neuron firmware initializes RAM to zero automatically when
the application is reset, a constant sequence should be designed with zero as its
initial value. The following section,
Take Advantage of Neuron Firmware
Default Initialization Actions , describes how you can use this fact to your
advantage.
Another consideration is a comparison, especially when used in a loop control
expression, such as in a while statement. The most efficient comparison of an
expression with a constant is when the constant is zero. If you cannot arrange to
have your loop test compare with zero, then try to arrange to have your loop test
compare with one. Equality comparisons with one are not as efficient as
comparisons with zero, but they are more efficient than comparisons with other
constants.
Take Advantage of Neuron Firmware Default
Initialization Actions
The Neuron firmware automatically sets all RAM variables to zero each time the
chip resets, and also when the Neuron C application_restart( ) function is called.
After this action, the Neuron C application program is started. The first action of
a Neuron C application program is to execute code to initialize any RAM
variables to non-zero values. Then, if a task associated with the when(reset)
clause exists, it is called.
Therefore, use of compile-time initializers to set RAM variables to zero is free.
Eliminate any code in the when(reset) clause’s task which is used to set RAM
variables to zero, because it is unnecessary.
Also, compile-time initializers of I/O output objects are free. They are free
regardless of initializer value. The use of compile-time initializers for I/O uses
less code space than corresponding calls to io_out( ) in the when(reset) clause’s
task.
Finally, during reset, the Neuron C application timers are all turned off
automatically. Eliminate any code in the when(reset) clause’s task that explicitly
turns off application timers.
Use Neuron C Utility Functions Effectively
There are several Neuron C utility functions that can be used to reduce code
requirements. For example, there are min( ), max( ), and abs( ) functions, as well
as other utility functions which can be used for common operations. Using these
functions is generally more code-space efficient than coding the operations in-line
using C operators.