feat(cpu): implement branch and exchange
If I want to continue with armwrestler, I'll have to implement THUMB instructions now
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@ -13,6 +13,7 @@ const singleDataTransfer = @import("cpu/single_data_transfer.zig").singleDataTra
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const halfAndSignedDataTransfer = @import("cpu/half_signed_data_transfer.zig").halfAndSignedDataTransfer;
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const blockDataTransfer = @import("cpu/block_data_transfer.zig").blockDataTransfer;
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const branch = @import("cpu/branch.zig").branch;
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const branchAndExchange = @import("cpu/branch.zig").branchAndExchange;
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pub const InstrFn = fn (*Arm7tdmi, *Bus, u32) void;
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const arm_lut: [0x1000]InstrFn = populate();
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@ -57,7 +58,7 @@ pub const Arm7tdmi = struct {
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fn fetch(self: *Self) u32 {
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const word = self.bus.read32(self.r[15]);
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self.r[15] += 4;
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self.r[15] += if (self.cpsr.t.read()) @as(u32, 2) else @as(u32, 4);
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return word;
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}
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@ -142,6 +143,10 @@ fn populate() [0x1000]InstrFn {
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lut[i] = psrTransfer(I, isSpsr);
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}
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if (i == 0x121) {
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lut[i] = branchAndExchange;
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}
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if (i >> 9 & 0x7 == 0b000 and i >> 3 & 1 == 1 and i & 1 == 1) {
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const P = i >> 8 & 1 == 1;
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const U = i >> 7 & 1 == 1;
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@ -1,3 +1,4 @@
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const std = @import("std");
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const util = @import("../util.zig");
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const Bus = @import("../Bus.zig");
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@ -16,3 +17,11 @@ pub fn branch(comptime L: bool) InstrFn {
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}
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}.inner;
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}
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pub fn branchAndExchange(cpu: *Arm7tdmi, _: *Bus, opcode: u32) void {
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const rn = opcode & 0xF;
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cpu.cpsr.t.write(cpu.r[rn] & 1 == 1);
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// TODO: Is this how I should do it?
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cpu.r[15] = cpu.r[rn] & 0xFFFF_FFFE;
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}
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