kernel.py

from process import Process

class Kernel:
    CPU_CODES = {
        0x00: "Halt code",
        0xAA: "Protection error",
        0xBB: "Invalid register",
        0xCC: "Unknown opcode",
        0xDD: "Unknown syscall",
        0xD0: "Awaiting syscall",
        0xFF: "Success code"
    }

    def __init__(self, mmu, cpu):
        self.processes:Process = []
        self.current = 0
        self.CPU = cpu
        self.MMU = mmu

    def create_process(self, program:Process, base_addr:int=0x00000, stack_top:int=0xFFFFF):
        process = Process(len(self.processes)) # len of processes -> pid
        bytes_used = 0
        for i, byte in enumerate(program):
            self.MMU.write_uint8(process, base_addr + i, byte)
            bytes_used += 1
        print(f"Loaded {bytes_used} bytes to memory")
        process.registers["sp"] = stack_top # top of virtual memory, grows downward
        process.registers["pc"] = base_addr # bottom of virtual memory, grows upward
        self.processes.append(process)
        return process

    def get_current_process(self):
        return self.processes[self.current]

    def schedule_next(self):
        self.current = (self.current + 1) % len(self.processes)

    def context_switch(self):
        current_process = self.get_current_process()
        current_process.registers = self.CPU.registers.copy()
        self.schedule_next()
        next_process = self.get_current_process()
        self.CPU.registers = next_process.registers.copy()

    def handle_syscall(self, process:Process):
        reg_index = process.registers["c0"] - 0xD0 # = r0...7
        syscall_code = process.registers[f"r{reg_index}"]

        match syscall_code:
            case 0x00:
                process.exit_code = process.registers["r1"]
                process.registers["c0"] = 0x00 # signal halt
                print(f"pid {process.pid} safe kernel exit")

            case 0xA0:
                print(f"pid {process.pid} console out: {process.registers["r1"]}")

            case _:
                print(f"pid {process.pid} unknown syscall")