User guide

4: ICP Download, Configuration, and Initialization
DC 900-1338I 75
3. Allocate space for the timer task’s stack and create the task.
4. Use the task initialization structures included in the configuration table to create
one or more application tasks.
5. Transfer control to the kernel’s dispatcher to begin normal run-time operations.
The timer task is the highest priority in the system and is dispatched first. It performs
certain initialization procedures and then stops, after which the other tasks that were
created are dispatched in order of priority.
4.3 Determining Configuration Parameters
Although the design of a system should never be constrained by its configuration, when
available memory is extremely limited or system performance is critical, it might be
wise to consider the relationship between the system configuration and OS/Impact’s
memory requirements and performance. These relationships are discussed in the fol-
lowing sections.
4.3.1 OS/Impact Memory Requirements
OS/Impact requires memory space for code, system data, stacks, and the exception vec-
tor table. Some data requirements are fixed, and some are dependent on the system
configuration. The space required for the exception vector table, code, and fixed data
for a particular version of the operating system can be found in
xio_nnnn.xrf for
xio_nnnn.mem. The number of bytes required for the system stacks and configurable
data structures can be calculated as shown in Tab le 4 –1.
Ta bl e 4 –2, which is based on the configuration shown previously in Figure 4–8 on
page 72, shows a sample calculation used to determine the total number of system data
bytes required. The total memory requirements for the system are calculated by adding
the total number of system bytes required to the ending address of the system services
module and rounding up, if necessary, to an even multiple of four bytes.