review

Output & structure: Code runs correctly,prints A–Z, 0–9, a–z in loop and handles input interrupts as expected.

Registers: All registers except k0/k1 preserved. Stack and .set noat/at used correctly.

Exceptions: Handler correctly distinguishes SYSCALL and ExtInt, others go to kernel_loop.

Status reg: Properly set to 0x0C03.

Scheduling: Round-robin works and each process resumes correctly.

Comments: Clear and helpful, easy to follow.

Suggestion: Add a short inline comment near curpcb update in timer handler for clarity.