Technique · engine

Cooperative multitasking

Running several jobs as tasks that each hand control back on their own, so one frame can resume many half-finished routines.

stubAlso: coroutines, task scheduler, cooperative threads, yielding scriptsUpdated 2026-10-25
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In cooperative multitasking, a scheduler runs several tasks in turn, and each task keeps control until it yields. A task that yields resumes where it stopped the next time it runs, so a routine can wait across frames without being split into states. On small machines each task may get its own slice of the stack, and object scripts can yield the same way.

  • Mega Man 6 (1993). Every object, Mega Man included, is a script that yields once a frame.1

See also

Games

GameYearHowNote
Mega Man 61993every object, Mega Man included, is a script that yields once a frame
Every claim about this mechanic, by game (2)
Mega Man 3 1990Both games run a stage a frame at a time in step with the NMI, but Mega Man 3's frame loop is new code built on a task scheduler. Mega Man 2's stage loop calls its routines in turn and then spins in _nmi_wait_0e until the NMI sets a flag, reading the pads after it. Mega Man 3 runs up to four tasks, each resumed from its own saved stack pointer; gameplay_frame_loop gives up the CPU for a frame through the scheduler, which reads the controllers only when it resumes task 0.Code
Mega Man 6 1993Mega Man 6 runs its objects, Mega Man included, as coroutines. Each frame code_3FE41C counts the slots from 22 down to 0 and calls each live one at its resume address ($0413/$042A); a script yields by calling code_3FE468, which pops its own return address into that pointer and moves to the next slot, so the script resumes after the call the next frame. Mega Man's movement (slot 0) is written as loops around that call, each loop ending the frame through code_388E95.Code

References

  1. ^Mega Man 6 runs its objects, Mega Man included, as coroutines. Each frame code_3FE41C counts the slots from 22 down to 0 and calls each live one at its resume address ($0413/$042A); a script yields by calling code_3FE468, which pops its own return address into that pointer and moves to the next slot, so the script resumes after the call the next frame. Mega Man's movement (slot 0) is written as loops around that call, each loop ending the frame through code_388E95.Coderefreshing-lemonade/megaman6-disassembly
    How we know
    20058loc_7E438:
    bank38_3F.asm lines 20056–20070 at f0763c4 · upstream ↗
    20081code_3FE468:
⋮
20090code_3FE477:
⋮
20093loc_7E47A:
    bank38_3F.asm lines 20081–20095 at f0763c4 · upstream ↗
    JMP code_3FE468
    bank38_3F.asm#L1976 · upstream ↗

    Checked against the evidence by its author, an AI model, 2026-10-25.

    Checked by a second AI model, 2026-10-25.

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