feat(cpu): implement branch and exchange

If I want to continue with armwrestler, I'll have to implement
THUMB instructions now
This commit is contained in:
Rekai Nyangadzayi Musuka 2022-01-12 07:14:41 -04:00
parent 7adc7c8802
commit 77dba68a0b
2 changed files with 15 additions and 1 deletions

View File

@ -13,6 +13,7 @@ const singleDataTransfer = @import("cpu/single_data_transfer.zig").singleDataTra
const halfAndSignedDataTransfer = @import("cpu/half_signed_data_transfer.zig").halfAndSignedDataTransfer;
const blockDataTransfer = @import("cpu/block_data_transfer.zig").blockDataTransfer;
const branch = @import("cpu/branch.zig").branch;
const branchAndExchange = @import("cpu/branch.zig").branchAndExchange;
pub const InstrFn = fn (*Arm7tdmi, *Bus, u32) void;
const arm_lut: [0x1000]InstrFn = populate();
@ -57,7 +58,7 @@ pub const Arm7tdmi = struct {
fn fetch(self: *Self) u32 {
const word = self.bus.read32(self.r[15]);
self.r[15] += 4;
self.r[15] += if (self.cpsr.t.read()) @as(u32, 2) else @as(u32, 4);
return word;
}
@ -142,6 +143,10 @@ fn populate() [0x1000]InstrFn {
lut[i] = psrTransfer(I, isSpsr);
}
if (i == 0x121) {
lut[i] = branchAndExchange;
}
if (i >> 9 & 0x7 == 0b000 and i >> 3 & 1 == 1 and i & 1 == 1) {
const P = i >> 8 & 1 == 1;
const U = i >> 7 & 1 == 1;

View File

@ -1,3 +1,4 @@
const std = @import("std");
const util = @import("../util.zig");
const Bus = @import("../Bus.zig");
@ -16,3 +17,11 @@ pub fn branch(comptime L: bool) InstrFn {
}
}.inner;
}
pub fn branchAndExchange(cpu: *Arm7tdmi, _: *Bus, opcode: u32) void {
const rn = opcode & 0xF;
cpu.cpsr.t.write(cpu.r[rn] & 1 == 1);
// TODO: Is this how I should do it?
cpu.r[15] = cpu.r[rn] & 0xFFFF_FFFE;
}