-
Notifications
You must be signed in to change notification settings - Fork 0
/
cpu.lua
197 lines (157 loc) · 3.71 KB
/
cpu.lua
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
local instructions = require "instructions"
local memory = nil
local bor, band, lshift, rshift = bit.bor, bit.band, bit.lshift, bit.rshift
local bxor = bit.bxor
local IE = 0xFFFF
local IF = 0xFF0F
local cpu = {
-- registers
a = 0,
f = 0,
b = 0,
c = 0,
d = 0,
e = 0,
h = 0,
l = 0,
pc = 0,
sp = 0,
ime = true,
halt = false,
cycles = 0,
-- current opcode, used in some instructions
opcode = 0,
memory = nil,
}
local interrupts = {
vblank = 0x01,
stat = 0x02,
timer = 0x04,
serial = 0x08,
joypad = 0x10,
}
local index = {
["(hl)"] = function(self)
return memory:get(bor(lshift(self.h, 8), self.l))
end,
["nn"] = function(self)
return memory:get(self.pc - 1)
end,
}
local newindex = {
["(hl)"] = function(self, value)
memory:set(bor(lshift(self.h, 8), self.l), value)
end,
["hl"] = function(self, value)
self.h = rshift(value, 8)
self.l = band(value, 0xff)
end,
}
function cpu:init(_memory)
self.pc = 0x0100
self.sp = 0xfffe
self.a = 0x01
self.f = 0xb0
self.b = 0x00
self.c = 0x13
self.d = 0x00
self.e = 0xd8
self.h = 0x01
self.l = 0x4d
memory = _memory
setmetatable(self, {
__index = function(tbl, key)
return index[key](tbl)
end,
__newindex = function(table, key, value)
newindex[key](table, value)
end,
})
end
function cpu:step()
self:check_interrupts()
if self.halt then
return 4
end
cpu.opcode = memory:get(self.pc)
local instr = instructions[cpu.opcode + 1]
local bytes, cycles, handler, params = instr[3], instr[4], instr[5], instr[6]
-- self:trace(instr)
self.pc = band(self.pc + bytes, 0xffff)
local extra_cycles = handler(params) or 0
self.cycles = self.cycles + cycles + extra_cycles
return cycles + extra_cycles
end
local interrupt_handlers = { 0x40, 0x48, 0x50, 0x58, 0x60 }
function cpu:check_interrupts()
local flags = memory:get(IF)
local interrupt = band(memory:get(IE), flags)
if interrupt ~= 0 then
self.halt = false
if self.ime then
-- no nested interrupts
self.ime = false
-- save pc
self:push(self.pc)
for index = 1, 5 do
local mask = lshift(1, index - 1)
if band(interrupt, mask) ~= 0 then
self.pc = interrupt_handlers[index]
memory:set(IF, band(flags, bxor(mask, 0xff)))
break
end
end
end
end
end
function cpu:conditional_interrupt(interrupt, value, mask)
if band(value, mask) ~= 0 then
self:interrupt(interrupt)
end
end
function cpu:push(value)
cpu.sp = cpu.sp - 2
memory:set(cpu.sp, band(value, 0xff))
memory:set(cpu.sp + 1, rshift(value, 0x8))
end
function cpu:pop()
local value = bor(memory:get(cpu.sp), lshift(memory:get(cpu.sp + 1), 8))
cpu.sp = cpu.sp + 2
return value
end
function cpu:interrupt(interrupt)
local interrupt_flag = memory:get(0xFF0F)
memory:set(0xFF0F, bor(interrupt_flag, interrupts[interrupt]))
end
function cpu:trace(instruction)
-- A:00 F:Z-H- BC:0000 DE:0393 HL:ffa8 SP:cfff PC:02f0
local z = band(cpu.f, 0x80) == 0x80 and "Z" or "-"
local s = band(cpu.f, 0x40) == 0x40 and "N" or "-"
local h = band(cpu.f, 0x20) == 0x20 and "H" or "-"
local c = band(cpu.f, 0x10) == 0x10 and "C" or "-"
local flags = z .. s .. h .. c
local data = ""
for i = 1, instruction[3] do
data = data .. string.format("%02x ", memory:get(self.pc + i - 1))
end
local opcode = memory:get(self.pc)
print(
string.format(
"A:%02X F:%s BC:%02X%02X DE:%02X%02X HL:%02X%02X SP:%04X PC:%04X (cy: %d) | %s [%s]",
cpu.a,
flags,
cpu.b,
cpu.c,
cpu.d,
cpu.e,
cpu.h,
cpu.l,
cpu.sp,
cpu.pc,
self.cycles,
instruction[2],
data
)
)
end
return cpu