多任务
首先创造两个任务：
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| void user_task0(void)
{
uart_puts("Task 0: Created!\n");
while (1) {
uart_puts("Task 0: Running...\n");
task_delay(DELAY);
task_yield();
}
}
void user_task1(void)
{
uart_puts("Task 1: Created!\n");
while (1) {
uart_puts("Task 1: Running...\n");
task_delay(DELAY);
task_yield();
}
}
C
|
这两个任务相当简单，就来回不断地打印信息。
接着创建这两个任务的栈区以及上下文：
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|
uint8_t __attribute__((aligned(16))) task_stack[MAX_TASKS][STACK_SIZE];
struct context ctx_tasks[MAX_TASKS];
int task_create(void (*start_routin)(void)) {
if (_top < MAX_TASKS) {
ctx_tasks[_top].sp = (reg_t)&task_stack[_top][STACK_SIZE];
ctx_tasks[_top].ra = (reg_t)start_routin;
_top++;
return 0;
} else {
return -1;
}
}
void os_main(void){
task_create(user_task0);
task_create(user_task1);
}
C
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接着，就可以调用 schedule 了：
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| void schedule() {
if (_top <= 0) {
panic("Num of task should be greater than zero!");
return;
}
_current = (_current + 1) % _top;
struct context* next = &(ctx_tasks[_current]);
switch_to(next);
}
C
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在 start_kernel 调用 schedule 之后，切换到 task0，接着 task0 调用 task_yield 切换到 task1。task1 也会调用 task_yield，结果就是两个任务来回切换：
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| Press Ctrl-A and then X to exit QEMU
------------------------------------
Hello, RVOS!
HEAP_START = 0x800070ec(aligned to 0x80008000), HEAP_SIZE = 0x07ff8f14,
num of reserved pages = 8, num of pages to be allocated for heap = 32752
TEXT: 0x80000000 -> 0x80003104
RODATA: 0x80003104 -> 0x80003354
DATA: 0x80004000 -> 0x80004004
BSS: 0x80004010 -> 0x800070ec
HEAP: 0x80010000 -> 0x88000000
Task 0: Created!
Task 0: Running...
Task 1: Created!
Task 1: Running...
Task 0: Running...
Task 1: Running...
Task 0: Running...
BASH
|
这就是多任务的切换。