268 lines
5.2 KiB
NASM
268 lines
5.2 KiB
NASM
; task switching routines
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; add a new task to the queue and jump to it immediately
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; inputs:
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; r0: task ID
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; r1: initial instruction pointer
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; r2: initial stack pointer (remember that the stack grows down!)
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; r3: pointer to code block to free when task ends, or zero for none
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; r4: pointer to stack block to free when task ends, or zero for none
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; outputs:
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; none
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new_task:
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; mark this task ID as used
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bse [task_id_bitmap], r0
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mov r6, r4 ; stack block pointer
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mov r5, r3 ; code block pointer
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mov r4, r2 ; stack pointer
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mov r3, r1 ; instruction pointer
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mov r2, r0 ; task ID
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; add to the queue
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mov r0, [task_queue_ptr]
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call task_store
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mov [task_queue_ptr], r0
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jmp save_state_and_yield_task
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; switch to the next task in the queue
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; no registers are saved upon task yield
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; if a register must be saved across a yield, push it before the yield and pop it after the yield
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; inputs:
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; none
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; outputs:
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; none
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yield_task:
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; add the current task back into the queue
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mov r0, current_task ; get the current task struct
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call task_load
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pop r3 ; pop the return address off of the stack
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mov r4, rsp
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mov r0, [task_queue_ptr]
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call task_store
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mov [task_queue_ptr], r0
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jmp yield_task_0
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; push all registers and switch to the next task in the queue
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; inputs:
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; none
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; outputs:
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; none
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save_state_and_yield_task:
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push rfp
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push r31
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push r30
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push r29
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push r28
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push r27
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push r26
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push r25
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push r24
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push r23
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push r22
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push r21
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push r20
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push r19
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push r18
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push r17
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push r16
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push r15
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push r14
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push r13
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push r12
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push r11
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push r10
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push r9
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push r8
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push r7
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push r6
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push r5
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push r4
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push r3
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push r2
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push r1
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push r0
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call yield_task
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pop r0
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pop r1
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pop r2
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pop r3
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pop r4
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pop r5
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pop r6
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pop r7
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pop r8
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pop r9
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pop r10
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pop r11
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pop r12
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pop r13
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pop r14
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pop r15
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pop r16
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pop r17
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pop r18
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pop r19
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pop r20
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pop r21
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pop r22
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pop r23
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pop r24
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pop r25
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pop r26
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pop r27
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pop r28
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pop r29
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pop r30
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pop r31
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pop rfp
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ret
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; switch to the next task without adding the current task back into the queue
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; this will automatically free the task's code and stack blocks
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; inputs:
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; none
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; outputs:
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; none
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end_current_task:
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mov r0, current_task ; get the current task struct
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call task_load
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bcl [task_id_bitmap], r2 ; mark this task ID as unused
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mov r0, r5 ; code block pointer
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cmp r0, 0
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ifnz call free_memory
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mov r0, r6 ; stack block pointer
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cmp r0, 0
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ifnz call free_memory
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end_current_task_no_mark_no_free:
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pop r0 ; pop the return address off of the stack
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cmp [task_queue_ptr], task_queue_bottom
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ifz jmp task_empty
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yield_task_0:
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mov r0, task_queue_bottom
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call task_load
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mov r0, current_task
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call task_store
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mov r1, task_queue_bottom
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yield_task_1:
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add r1, TASK_SIZE
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cmp [task_queue_ptr], r1
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ifz jmp yield_task_2
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mov r0, r1
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call task_load
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mov r0, r1
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sub r0, TASK_SIZE
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call task_store
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jmp yield_task_1
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yield_task_2:
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mov r0, current_task
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call task_load
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sub [task_queue_ptr], TASK_SIZE
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mov rsp, r4
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jmp r3
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; get the next unused task ID, starting at 1
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; inputs:
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; none
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; outputs:
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; r0: task ID, or zero if all IDs are used
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get_unused_task_id:
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mov r0, 1
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get_unused_task_id_loop:
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bts [task_id_bitmap], r0
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ifz ret
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inc r0
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cmp r0, 32
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iflt jmp get_unused_task_id_loop
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; if we reach this point, then all task IDs are used
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mov r0, 0
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ret
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; get the task ID of the currently running task
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; inputs:
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; none
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; outputs:
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; r0: task ID
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get_current_task_id:
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push r2
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push r3
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push r4
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push r5
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push r6
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mov r0, current_task
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call task_load
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mov r0, r2
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pop r6
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pop r5
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pop r4
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pop r3
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pop r2
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ret
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; check if a task ID is used
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; inputs:
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; r0: task ID
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; outputs:
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; Z flag: set if unused, reset if used
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is_task_id_used:
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bts [task_id_bitmap], r0
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ret
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task_load:
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mov r2, [r0] ; task ID
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add r0, 4
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mov r3, [r0] ; instruction pointer
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add r0, 4
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mov r4, [r0] ; stack pointer
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add r0, 4
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mov r5, [r0] ; code block pointer
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add r0, 4
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mov r6, [r0] ; stack block pointer
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add r0, 4
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ret
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task_store:
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mov [r0], r2 ; task ID
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add r0, 4
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mov [r0], r3 ; instruction pointer
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add r0, 4
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mov [r0], r4 ; stack pointer
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add r0, 4
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mov [r0], r5 ; code block pointer
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add r0, 4
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mov [r0], r6 ; stack block pointer
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add r0, 4
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ret
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task_empty:
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mov r0, task_panic_str
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mov r1, task_queue_bottom ; show the address of the task queue in the panic brk output
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mov r2, [task_queue_ptr] ; show the the task queue pointer in the panic brk output
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call panic
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task_panic_str: data.str "Scheduler starved, task queue empty!" data.8 10 data.8 0
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const TASK_SIZE: 20
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task_id_bitmap: data.32 0
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current_task:
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data.32 0 ; task ID
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data.32 0 ; instruction pointer
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data.32 0 ; stack pointer
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data.32 0 ; code block pointer
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data.32 0 ; stack block pointer
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task_queue_ptr: data.32 task_queue_bottom
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task_queue_bottom: data.fill 0, 640 ; 32 tasks * 5 entries per task * 4 bytes per word = 640
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