m68k 0.2.1

A safe Rust M68000 family CPU emulator
Documentation 
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

//! Bit manipulation instructions.
//!
//! BTST, BSET, BCLR, BCHG

use crate::core::cpu::CpuCore;
use crate::core::ea::AddressingMode;
use crate::core::memory::AddressBus;
use crate::core::types::Size;

impl CpuCore {
    /// Execute BTST instruction.
    ///
    /// BTST Dn/<#data>, <ea>
    pub fn exec_btst<B: AddressBus>(
        &mut self,
        bus: &mut B,
        bit_num: u32,
        mode: AddressingMode,
    ) -> i32 {
        // Register operand: modulo 32, memory operand: modulo 8
        let (size, bit) = if mode.is_register_direct() {
            (Size::Long, bit_num & 31)
        } else {
            (Size::Byte, bit_num & 7)
        };

        let value = self.read_ea(bus, mode, size);
        self.not_z_flag = if value & (1 << bit) != 0 { 1 } else { 0 };

        if size == Size::Long {
            6
        } else {
            let base = if matches!(mode, AddressingMode::Immediate) {
                6
            } else {
                4
            };
            base + self.ea_time(mode, Size::Byte)
        }
    }

    /// Execute BSET instruction.
    ///
    /// BSET Dn/<#data>, <ea>
    pub fn exec_bset<B: AddressBus>(
        &mut self,
        bus: &mut B,
        bit_num: u32,
        mode: AddressingMode,
    ) -> i32 {
        let (size, bit) = if mode.is_register_direct() {
            (Size::Long, bit_num & 31)
        } else {
            (Size::Byte, bit_num & 7)
        };

        let ea = self.resolve_ea(bus, mode, size);
        let value = self.read_resolved_ea(bus, ea, size);
        self.not_z_flag = if value & (1 << bit) != 0 { 1 } else { 0 };
        let result = value | (1 << bit);
        self.write_resolved_ea(bus, ea, size, result & size.mask());

        if size == Size::Long {
            if self.is_pre_68020 {
                if bit >= 16 { 8 } else { 6 }
            } else {
                8
            }
        } else {
            8 + self.ea_time(mode, Size::Byte)
        }
    }

    /// Execute BCLR instruction.
    ///
    /// BCLR Dn/<#data>, <ea>
    pub fn exec_bclr<B: AddressBus>(
        &mut self,
        bus: &mut B,
        bit_num: u32,
        mode: AddressingMode,
    ) -> i32 {
        let (size, bit) = if mode.is_register_direct() {
            (Size::Long, bit_num & 31)
        } else {
            (Size::Byte, bit_num & 7)
        };

        let ea = self.resolve_ea(bus, mode, size);
        let value = self.read_resolved_ea(bus, ea, size);
        self.not_z_flag = if value & (1 << bit) != 0 { 1 } else { 0 };
        let result = value & !(1 << bit);
        self.write_resolved_ea(bus, ea, size, result & size.mask());

        if size == Size::Long {
            if self.is_pre_68020 {
                if bit >= 16 { 10 } else { 8 }
            } else {
                10
            }
        } else {
            8 + self.ea_time(mode, Size::Byte)
        }
    }

    /// Execute BCHG instruction.
    ///
    /// BCHG Dn/<#data>, <ea>
    pub fn exec_bchg<B: AddressBus>(
        &mut self,
        bus: &mut B,
        bit_num: u32,
        mode: AddressingMode,
    ) -> i32 {
        let (size, bit) = if mode.is_register_direct() {
            (Size::Long, bit_num & 31)
        } else {
            (Size::Byte, bit_num & 7)
        };

        let ea = self.resolve_ea(bus, mode, size);
        let value = self.read_resolved_ea(bus, ea, size);
        self.not_z_flag = if value & (1 << bit) != 0 { 1 } else { 0 };
        let result = value ^ (1 << bit);
        self.write_resolved_ea(bus, ea, size, result & size.mask());

        if size == Size::Long {
            if self.is_pre_68020 {
                if bit >= 16 { 8 } else { 6 }
            } else {
                8
            }
        } else {
            8 + self.ea_time(mode, Size::Byte)
        }
    }

    /// Execute TAS instruction.
    ///
    /// TAS <ea>
    pub fn exec_tas<B: AddressBus>(&mut self, bus: &mut B, mode: AddressingMode) -> i32 {
        let ea = self.resolve_ea(bus, mode, Size::Byte);
        let value = self.read_resolved_ea(bus, ea, Size::Byte);
        self.set_logic_flags(value, Size::Byte);

        // Set bit 7
        let result = value | 0x80;
        self.write_resolved_ea(bus, ea, Size::Byte, result);

        if self.is_pre_68020 && !mode.is_register_direct() {
            10 + self.ea_time(mode, Size::Byte)
        } else {
            4
        }
    }
}