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Master the fundamental concepts of protected mode transition through this focused micro-challenge.
You have read the whole brief, and the concepts above stay free on every task. Writing and running the code needs a plan.
Three hints are available for this task, revealed one at a time inside the code workspace so you can struggle productively before seeing them.
Every task includes starter code, theory, and hidden tests so you can implement and verify locally in the browser.
How it worksIn protected mode the IDT holds 8-byte gate descriptors pointing to handlers with privilege and type information. LIDT loads the table base and limit; each interrupt index selects an entry. For example, entry 32 (IRQ0 after PIC remap) needs a present interrupt gate targeting your timer ISR at ring 0.
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0x20-0x2F before unmasking IRQsIRETD in 32-bit codeDivide-by-zero and invalid opcode handlers help catch early PM bugs. Place stubs in low memory or identity-mapped regions so their addresses fit gate offset fields. Use interrupt gates (type 0x8E) not trap gates unless you need nested faults on the same vector. Double-fault requires a valid TSS stack if you run ring 3 later; for ring 0 only labs, a simple halt loop in the handler is enough.
You will pack and unpack the 8-byte gate descriptors, register handlers in a simulated IDT, and trace interrupt dispatch, including which PICs need an EOI. This exercise requires matching gate selectors to your GDT code segment and using IRETD return.
Implement IDT gate encoding, decoding, and dispatch simulation in C, driven by a command script on stdin.
Protocol (all numbers in hex):
Process every command on stdin until EOF, printing one line per command.