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eplaces the old recipe number and the control variable is set to 1.
In order to avoid invalid memory accesses, recipe number input is checked for the max. available recipes.
The second IF−statement is fulfilled if the control variable 0. In other words, the dynamic variable references
the current recipe number.
(* cyclic program *)
if (recipeNrAct recipeNrOld) then
if (recipeNrAct > 5) then
recipeNrAct = 5;
endif
recipeChanged = 1;
recipeNrOld = recipeNrAct;
endif
if (recipeChanged > 0) then
pRec access adr(rec_arr[recipeNrAct−1]);
recipeChanged = 0;
endif
Read the Notes at the end of the chapter.
4.12.7.4 Code in ANSI C
The code described above in C:
#include
#include struct recipe { unsigned long elem1; unsigned long elem2;
unsigned long elem3; unsigned long elem4; unsigned long elem5; }; struct recipe rec_arr[5]; _GLOBAL
unsigned char recipeNrAct; _GLOBAL unsigned char recipeNrOld; _GLOBAL unsigned char recipeChanged;
_LOCAL struct recipe *pRec; _INIT init_func(void) { int i; for(i = 0; i < 5; i++) { rec_arr[i].elem1
= 100 * i + 1; rec_arr[i].elem2 = 100 * i + 2; rec_arr[i].elem3 = 100 * i + 3; rec_arr[i].elem4 =
100 * i + 4; rec_arr[i].elem5 = 100 * i + 5; } recipeNrAct = 1; recipeNrOld = 0; recipeChanged = 0;
} _CYCLIC cyc_func(void) { if(recipeNrAct != recipeNrOld) { if(recipeNrAct > 5) { recipeNrAct = 5; }
recipeChanged = 1; recipeNrOld = recipeNrAct; } if(recipeChanged > 0) { pRec =
&rec_arr[recipeNrAct−1]; recipeChanged = 0; } }
4.12.7.4.1 Important notes
A dynamic variable does not limit itself to referencing static variables of the same data type; rather, it can
reference any memory address. However, this can lead to big problems. When using dynamic variables, it
should be noted that they should already be initialized when first accessed (null pointer error) and not pointed to
an invalid memory range during runtime.
If limits were not set for the max. recipe number in the above example, a value of another variable or even
program code could have possibly been overwritten. This can crash a program or cause invalid data to be
displayed.
4.12.8 VC System Tuning
All Visual Components runtime modules are tied to the system as non−cyclic tasks with lower priority than cyclic
tasks. Cyclic user tasks (task classes) are therefore not influenced by runtime performance. Visual Components
runtime modules run in the system idle time with low priority.
A simple and clear definition of timing performance is difficult because of the different ways that application
software loads down the CPU. This is mainly due to the lower priority of Visual Components runtime modules.
If a system does not have much idle time available, then display speed and key reaction are slower on the target
system. Therefore, attention should be paid to how much idle time is available on the system. An 'unfavorable'
configuration example will show how this works in practice.
We will use the following configuration:
Introduction to Visual Components 2.3
432 4.12.7.4 Code in ANSI C