kernel: Add `sleep_task`

fox32os.def

@@ -20,6 +20,7 @@ get_current_task_id:       jmp [0x00000A1C]
 get_unused_task_id:        jmp [0x00000A20]
 is_task_id_used:           jmp [0x00000A24]
 save_state_and_yield_task: jmp [0x00000A28]
+sleep_task:                jmp [0x00000A2C]
 
 ; memory jump table
 allocate_memory:           jmp [0x00000B10]

kernel/main.asm

@@ -42,6 +42,7 @@ jump_table:
     data.32 get_unused_task_id
     data.32 is_task_id_used
     data.32 save_state_and_yield_task
+    data.32 sleep_task
 
     ; memory jump table
     org.pad 0x00000310

kernel/task.asm

@@ -122,6 +122,27 @@ save_state_and_yield_task:
     pop rfp
     ret
 
+; yield for at least the specified number of ms
+; inputs:
+; r0: minimum ms to yield for
+; outputs:
+; none
+sleep_task:
+    push r0
+    push r1
+
+    in r1, 0x80000706
+    add r0, r1
+sleep_task_loop:
+    call save_state_and_yield_task
+    in r1, 0x80000706
+    cmp r1, r0
+    iflt jmp sleep_task_loop
+
+    pop r1
+    pop r0
+    ret
+
 ; switch to the next task without adding the current task back into the queue
 ; this will automatically free the task's code and stack blocks
 ; inputs: