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use endian;
use io;
use os;
use fs;
use fmt;
type stack_overflow = !void;
type stack_underflow = !void;
type cpu = struct {
sp: u8,
rp: u8,
pc: u16,
mem: []u8,
halted: bool,
};
fn cpu_new() cpu = cpu {
sp = 0,
rp = 0,
pc = 0x0200,
mem = alloc([0...], 65536): []u8,
halted = false,
};
fn rmem(mem: []u8, addr: u16) u16 =
endian::begetu16(mem[addr..addr+2]);
fn wmem(mem: []u8, addr: u16, w: u16) void =
endian::beputu16(mem[addr..addr+2], w);
// stacks grow up, for a change
fn push(cpu: *cpu, val: u16) void = {
wmem(cpu.mem, 0 + cpu.sp, val);
cpu.sp += 2;
};
fn pop(cpu: *cpu) u16 = {
cpu.sp -= 2;
return rmem(cpu.mem, 0 + cpu.sp);
};
fn peek(cpu: *cpu, n: u16 = 0) u16 =
rmem(cpu.mem, 0 + cpu.sp - 2 + n);
fn rpush(cpu: *cpu, val: u16) void = {
wmem(cpu.mem, 0x100 + cpu.rp:u16, val);
cpu.rp += 2;
};
fn rpop(cpu: *cpu) u16 = {
cpu.rp -= 2;
return rmem(cpu.mem, 0x100 + cpu.rp:u16);
};
def MASK_CALL: u16 = 0b1000000000000000;
def MASK_LIT : u16 = 0b0110000000000000;
def MASK_JMP : u16 = 0b0100000000000000;
fn maskeq(x: u16, m: u16) bool =
// still must be called in the right order
(x&m) == m;
fn do_word(cpu: *cpu, word: u16) void = {
if (maskeq(word, MASK_CALL)) {
const addr = word & 0b0111111111111111;
const addr = addr << 1;
do_call(cpu, addr);
} else if (maskeq(word, MASK_LIT)) {
const lval = word & 0b0001111111111111;
push(cpu, lval);
} else if (maskeq(word, MASK_JMP)) {
const is_cond = (word & 0b0001000000000000) != 0;
const rel: u16 = word & 0b0000111111111111;
const rel: i16 = rel:i16 - 2048i16;
const target: i16 = rel + cpu.pc:i16 - 2i16;
const target: u16 = target:u16;
if (is_cond)
do_0branch(cpu, target)
else
do_jmp(cpu, target);
} else {
const opc1: u8 = ((word & 0b0011111110000000) >> 7):u8;
const opc2: u8 = (word & 0b0000000001111111):u8;
do_opc(cpu, opc1);
do_opc(cpu, opc2);
};
};
fn do_call(cpu: *cpu, addr: u16) void = {
rpush(cpu, cpu.pc);
cpu.pc = addr;
};
fn do_jmp(cpu: *cpu, addr: u16) void = {
cpu.pc = addr;
};
fn do_0branch(cpu: *cpu, addr: u16) void = {
const val = pop(cpu);
if (val == 0) {
cpu.pc = addr;
};
};
fn mainloop(cpu: *cpu) void = {
for (! cpu.halted) {
const word = rmem(cpu.mem, cpu.pc);
cpu.pc += 2;
do_word(cpu, word);
};
};
export fn main() void = {
const cpu = cpu_new();
const fp = match (os::open("sys0.r1b")) {
case let i: io::file => yield i;
case let e: fs::error => fmt::fatalf("MISSING BOOT SECTOR: {}",
fs::strerror(e));
};
match (io::readall(fp, cpu.mem[0x0200..0x0300])) {
case let e: io::error => fmt::fatalf("BOOT SECTOR READ ERROR: {}", io::strerror(e));
case => yield;
};
mainloop(&cpu);
};
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