nx_kernel_sched_test.nx

nx_kernel_sched_test.nx -- x86 ladder R-kernel rung-1: a SCHEDULER (the heart of an OS). A boot+loader gets code running; what makes it an OPERATING SYSTEM is multitasking: more than one task, with a real CONTEXT SWITCH between them. This builds two tiny x86 tasks and a cooperative round-robin scheduler. The emu is made RESUMABLE: emu_resume runs a task from its saved state until it executes YIELD (0xF1), saving its registers + pc into a per-task control block, so the scheduler can switch to the other task and come back exactly where it left off. The proof of a REAL context switch: each task sets rdx=0x3F8 (the UART port) ONCE before its loop; on every resume it re-enters mid-loop WITHOUT re-setting rdx, so each of its prints only works if the scheduler RESTORED rdx across the switch. Task A prints 'A' then yields; task B prints 'B' then yields. Round-robin for 4 rounds must produce exactly "ABABABAB" -- fair, no starvation, context preserved. KAT: console == "ABABABAB", both tasks alive (not halted), equal progress (4 each). HONEST SCOPE: COOPERATIVE (yield-based) on one core. PREEMPTIVE scheduling (timer IRQ0 via the PIC + IDT) is the next rung; then memory manager, syscalls, userspace. No hw writes (Rule 26). expect_exit: 0 license_tier: ORIGINAL