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const std = @import("std");
const log = std.log.scoped(.SPU_2_Interpreter);
const spu = @import("../spu-mk2.zig");
const FlagRegister = spu.FlagRegister;
const Instruction = spu.Instruction;
const ExecutionCondition = spu.ExecutionCondition;
pub fn Interpreter(comptime Bus: type) type {
return struct {
ip: u16 = 0,
sp: u16 = undefined,
bp: u16 = undefined,
fr: FlagRegister = @bitCast(FlagRegister, @as(u16, 0)),
/// This is set to true when we hit an undefined0 instruction, allowing it to
/// be used as a trap for testing purposes
undefined0: bool = false,
/// This is set to true when we hit an undefined1 instruction, allowing it to
/// be used as a trap for testing purposes. undefined1 is used as a breakpoint.
undefined1: bool = false,
bus: Bus,
pub fn ExecuteBlock(self: *@This(), comptime size: ?u32) !void {
var count: usize = 0;
while (size == null or count < size.?) {
count += 1;
var instruction = @bitCast(Instruction, self.bus.read16(self.ip));
log.debug("Executing {}\n", .{instruction});
self.ip +%= 2;
const execute = switch (instruction.condition) {
.always => true,
.not_zero => !self.fr.zero,
.when_zero => self.fr.zero,
.overflow => self.fr.carry,
ExecutionCondition.greater_or_equal_zero => !self.fr.negative,
else => return error.Unimplemented,
};
if (execute) {
const val0 = switch (instruction.input0) {
.zero => @as(u16, 0),
.immediate => i: {
const val = self.bus.read16(@intCast(u16, self.ip));
self.ip +%= 2;
break :i val;
},
else => |e| e: {
// peek or pop; show value at current SP, and if pop, increment sp
const val = self.bus.read16(self.sp);
if (e == .pop) {
self.sp +%= 2;
}
break :e val;
},
};
const val1 = switch (instruction.input1) {
.zero => @as(u16, 0),
.immediate => i: {
const val = self.bus.read16(@intCast(u16, self.ip));
self.ip +%= 2;
break :i val;
},
else => |e| e: {
// peek or pop; show value at current SP, and if pop, increment sp
const val = self.bus.read16(self.sp);
if (e == .pop) {
self.sp +%= 2;
}
break :e val;
},
};
const output: u16 = switch (instruction.command) {
.get => self.bus.read16(self.bp +% (2 *% val0)),
.set => a: {
self.bus.write16(self.bp +% 2 *% val0, val1);
break :a val1;
},
.load8 => self.bus.read8(val0),
.load16 => self.bus.read16(val0),
.store8 => a: {
const val = @truncate(u8, val1);
self.bus.write8(val0, val);
break :a val;
},
.store16 => a: {
self.bus.write16(val0, val1);
break :a val1;
},
.copy => val0,
.add => a: {
var val: u16 = undefined;
self.fr.carry = @addWithOverflow(u16, val0, val1, &val);
break :a val;
},
.sub => a: {
var val: u16 = undefined;
self.fr.carry = @subWithOverflow(u16, val0, val1, &val);
break :a val;
},
.spset => a: {
self.sp = val0;
break :a val0;
},
.bpset => a: {
self.bp = val0;
break :a val0;
},
.frset => a: {
const val = (@bitCast(u16, self.fr) & val1) | (val0 & ~val1);
self.fr = @bitCast(FlagRegister, val);
break :a val;
},
.bswap => (val0 >> 8) | (val0 << 8),
.bpget => self.bp,
.spget => self.sp,
.ipget => self.ip +% (2 *% val0),
.lsl => val0 << 1,
.lsr => val0 >> 1,
.@"and" => val0 & val1,
.@"or" => val0 | val1,
.xor => val0 ^ val1,
.not => ~val0,
.undefined0 => {
self.undefined0 = true;
// Break out of the loop, and let the caller decide what to do
return;
},
.undefined1 => {
self.undefined1 = true;
// Break out of the loop, and let the caller decide what to do
return;
},
.signext => if ((val0 & 0x80) != 0)
(val0 & 0xFF) | 0xFF00
else
(val0 & 0xFF),
else => return error.Unimplemented,
};
switch (instruction.output) {
.discard => {},
.push => {
self.sp -%= 2;
self.bus.write16(self.sp, output);
},
.jump => {
self.ip = output;
},
else => return error.Unimplemented,
}
if (instruction.modify_flags) {
self.fr.negative = (output & 0x8000) != 0;
self.fr.zero = (output == 0x0000);
}
} else {
if (instruction.input0 == .immediate) self.ip +%= 2;
if (instruction.input1 == .immediate) self.ip +%= 2;
break;
}
}
}
};
}
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