165 lines
3.8 KiB
NASM
165 lines
3.8 KiB
NASM
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; 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: task instruction pointer
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; r2: task stack pointer
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; outputs:
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; none
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new_task:
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bse [task_id_bitmap], r0 ; mark this task ID as used
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mov r4, r2
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mov r3, r1
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mov r2, r0
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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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; fall-through
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; 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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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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; switch to the next task without adding the current task back into 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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end_current_task:
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cmp [task_queue_ptr], task_queue_bottom
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ifz jmp task_empty
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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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pop r0 ; pop the return address off of the stack
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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 add task IDs are used
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mov r0, 0
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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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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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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 "Task queue empty! Hanging here" data.8 10 data.8 0
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const TASK_SIZE: 12
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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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task_queue_ptr: data.32 task_queue_bottom
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task_queue_bottom:
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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data.32 0 data.32 0 data.32 0
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