Start
• Task
Function •
Scheduling
and Timeslice •
Task
Context •
Task
Control Block •
Global
Variables •
Memory
Management •
API
•
Assembly
Functions •
Give
it a Try •
Enhancements
•
References,
Sources & PDF
MEMORY
MANAGEMENT
µexec needs to allocate
memory to hold the task-control blocks and the tasks’
stacks. This allocation can be done by using the C-library
function memory-management routines malloc and free
or by using statically allocated global arrays.
Since µexec is meant
to be used in a small system, the overhead of and
possible fragmentation of the memory space by using
malloc and free are of concern. So, we use a simple
array allocator instead. However, you can easily modify
the system to use malloc and free.
Task stacks are supplied
as an argument to UEXC_CreateTask. You should define
statically allocated arrays and supply them to UEXC_CreateTask:
static unsigned char
task_stack[UEXC_MIN_STACK_SIZE];
All the task-control
blocks are allocated from a global array:
static TaskControlBlock
free_list[NUM_TASKS], *free_list_ptr;
A task-control block
is allocated from the free_list_ptr every time a task
is created. UEXC_Createtask fails if no more task-control
blocks are available.
The system initializes
free_list_ ptr with the elements in free_list, so
you can adjust the total number of task-control blocks
by changing the value of NUM_TASKS. When a task is
killed or when a task function returns, its task-control
block is released back to the free_list_ptr pool.
