Echelon Neuron C - Manual (Page 32)

20 Focusing on a Single Device
io_changes). These operators are of equal precedence with each other, but they
are mutually exclusive. They are of higher precedence than relational operators
(that is, comparisons), but lower in precedence than shift and arithmetic
operators.
Following are examples of how the io_changes event expression is parsed:
io_changes ( device ) by a + b
as:
io_changes (
device ) by (a + b)
and
io_changes (
device ) by a < b
as:
(io_changes ( device ) by a) < b
As with any other C operators, the implied precedence can be explicitly changed
by parenthesization. Parentheses should
always be used to improve clarity of the
code if there is any doubt. Use of extra parentheses has no negative effect upon
the compilation or the code generated.
The Neuron C compiler detects the use of predefined event keywords in when
clauses and treats them specially for code optimization purposes. However, when
event keywords are used as sub-expressions within when clauses, event table
optimizations cannot be used. In the examples below, the first case uses the
event table optimization, the second and third do not:
when (timer_expires) { }
when (! timer_expires) { }
if (timer_expires)
Although the io_changes expression (by and to varieties) does not require a
constant value, only constant-valued io_changes expressions are optimized into
the when clause event table.
Event Processing
Events related to network activity are processed using two separate queues. One
queue serves the following events related to incoming network messages:
nv_update_occurs
msg_arrives
online
offline
wink
The other queue serves the remaining network events pertaining to completion
events and responses:
nv_update_completes
nv_update_succeeds
nv_update_fails
msg_completes