62 lines
1.5 KiB
Zig
62 lines
1.5 KiB
Zig
const io = @import("../../bus/io.zig");
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const ToneSweep = @import("../ToneSweep.zig");
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const Self = @This();
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timer: u8,
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enabled: bool,
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shadow: u11,
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calc_performed: bool,
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pub fn create() Self {
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return .{
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.timer = 0,
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.enabled = false,
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.shadow = 0,
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.calc_performed = false,
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};
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}
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pub fn reset(self: *Self) void {
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self.timer = 0;
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self.enabled = false;
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self.shadow = 0;
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self.calc_performed = false;
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}
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pub fn tick(self: *Self, ch1: *ToneSweep) void {
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if (self.timer != 0) self.timer -= 1;
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if (self.timer == 0) {
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const period = ch1.sweep.period.read();
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self.timer = if (period == 0) 8 else period;
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if (self.enabled and period != 0) {
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const new_freq = self.calculate(ch1.sweep, &ch1.enabled);
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if (new_freq <= 0x7FF and ch1.sweep.shift.read() != 0) {
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ch1.freq.frequency.write(@truncate(u11, new_freq));
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self.shadow = @truncate(u11, new_freq);
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_ = self.calculate(ch1.sweep, &ch1.enabled);
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}
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}
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}
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}
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/// Calculates the Sweep Frequency
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pub fn calculate(self: *Self, sweep: io.Sweep, ch_enable: *bool) u12 {
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const shadow = @as(u12, self.shadow);
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const shadow_shifted = shadow >> sweep.shift.read();
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const decrease = sweep.direction.read();
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const freq = if (decrease) blk: {
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self.calc_performed = true;
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break :blk shadow - shadow_shifted;
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} else shadow + shadow_shifted;
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if (freq > 0x7FF) ch_enable.* = false;
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return freq;
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}
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