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diff --git a/src/peripherals/timer-attiny.ts b/src/peripherals/timer-attiny.ts
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+// SPDX-License-Identifier: MIT
+// Copyright (c) Uri Shaked and contributors
+
+/**
+ * ATtiny25/45/85 Timer/Counter1
+ * Part of AVR8js
+ * Reference: http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-2586-AVR-8-bit-Microcontroller-ATtiny25-ATtiny45-ATtiny85_Datasheet.pdf
+ */
+
+import { AVRInterruptConfig, CPU, CPUMemoryHook } from '../cpu/cpu';
+import { PinOverrideMode } from './gpio';
+
+type u8 = number;
+type u16 = number;
+
+export interface ATtinyTimer1Config {
+  TCCR1: u8;
+  GTCCR: u8;
+  TCNT1: u8;
+  OCR1A: u8;
+  OCR1B: u8;
+  OCR1C: u8;
+  TIFR: u8;
+  TIMSK: u8;
+
+  ovfInterrupt: u8;
+  compAInterrupt: u8;
+  compBInterrupt: u8;
+
+  TOV1: u8;
+  OCF1A: u8;
+  OCF1B: u8;
+
+  TOIE1: u8;
+  OCIE1A: u8;
+  OCIE1B: u8;
+
+  compPortB: u16;
+  compPinA: u8;
+  compPinB: u8;
+
+  dividers: Record<number, number>;
+}
+
+// TCCR1 bits
+const CTC1 = 1 << 7;
+const PWM1A = 1 << 6;
+const CS_MASK = 0x0f;
+
+// GTCCR bits
+const PWM1B_BIT = 1 << 6;
+const FOC1B = 1 << 3;
+const FOC1A = 1 << 2;
+const PSR1 = 1 << 1;
+
+export const attinyTimer1Config: ATtinyTimer1Config = {
+  TCCR1: 0x50,
+  GTCCR: 0x4c,
+  TCNT1: 0x4f,
+  OCR1A: 0x4e,
+  OCR1B: 0x4b,
+  OCR1C: 0x4d,
+  TIFR: 0x58,
+  TIMSK: 0x59,
+
+  ovfInterrupt: 0x04,
+  compAInterrupt: 0x03,
+  compBInterrupt: 0x09,
+
+  TOV1: 1 << 2,
+  OCF1A: 1 << 6,
+  OCF1B: 1 << 5,
+
+  TOIE1: 1 << 2,
+  OCIE1A: 1 << 6,
+  OCIE1B: 1 << 5,
+
+  compPortB: 0x38,
+  compPinA: 1, // PB1
+  compPinB: 4, // PB4
+
+  dividers: {
+    0: 0,
+    1: 1,
+    2: 2,
+    3: 4,
+    4: 8,
+    5: 16,
+    6: 32,
+    7: 64,
+    8: 128,
+    9: 256,
+    10: 512,
+    11: 1024,
+    12: 2048,
+    13: 4096,
+    14: 8192,
+    15: 16384,
+  },
+};
+
+export class ATtinyTimer1 {
+  private lastCycle = 0;
+  private tcnt = 0;
+  private tcntNext = 0;
+  private tcntUpdated = false;
+  private ocrA = 0;
+  private ocrB = 0;
+  private ocrC = 0;
+  private divider = 0;
+  private updateDivider = false;
+  private countingUp = true;
+
+  private readonly OVF: AVRInterruptConfig = {
+    address: this.config.ovfInterrupt,
+    flagRegister: this.config.TIFR,
+    flagMask: this.config.TOV1,
+    enableRegister: this.config.TIMSK,
+    enableMask: this.config.TOIE1,
+  };
+
+  private readonly OCFA: AVRInterruptConfig = {
+    address: this.config.compAInterrupt,
+    flagRegister: this.config.TIFR,
+    flagMask: this.config.OCF1A,
+    enableRegister: this.config.TIMSK,
+    enableMask: this.config.OCIE1A,
+  };
+
+  private readonly OCFB: AVRInterruptConfig = {
+    address: this.config.compBInterrupt,
+    flagRegister: this.config.TIFR,
+    flagMask: this.config.OCF1B,
+    enableRegister: this.config.TIMSK,
+    enableMask: this.config.OCIE1B,
+  };
+
+  constructor(
+    private cpu: CPU,
+    private config: ATtinyTimer1Config,
+  ) {
+    const { TCCR1, GTCCR, TCNT1, OCR1A, OCR1B, OCR1C, TIFR, TIMSK } = config;
+
+    cpu.readHooks[TCNT1] = () => {
+      this.count(false);
+      return (cpu.data[TCNT1] = this.tcnt & 0xff);
+    };
+
+    cpu.writeHooks[TCNT1] = (value: number) => {
+      this.tcntNext = value;
+      this.countingUp = true;
+      this.tcntUpdated = true;
+      cpu.updateClockEvent(this.count, 0);
+      if (this.divider) {
+        this.timerUpdated(this.tcntNext, this.tcntNext);
+      }
+    };
+
+    cpu.writeHooks[OCR1A] = (value: number) => {
+      this.ocrA = value;
+    };
+    cpu.writeHooks[OCR1B] = (value: number) => {
+      this.ocrB = value;
+    };
+    cpu.writeHooks[OCR1C] = (value: number) => {
+      this.ocrC = value;
+    };
+
+    cpu.writeHooks[TCCR1] = (value: number) => {
+      cpu.data[TCCR1] = value;
+      this.updateDivider = true;
+      cpu.clearClockEvent(this.count);
+      cpu.addClockEvent(this.count, 0);
+      this.updateCompConfig();
+      return true;
+    };
+
+    // GTCCR is shared with Timer0 (PSR0) — chain with existing hook
+    const prevGtccrHook = cpu.writeHooks[GTCCR] as CPUMemoryHook | undefined;
+    cpu.writeHooks[GTCCR] = (value: number, oldValue: number, addr: number, mask: number) => {
+      if (value & FOC1A) {
+        this.forceCompare('A');
+      }
+      if (value & FOC1B) {
+        this.forceCompare('B');
+      }
+      if (value & PSR1) {
+        this.lastCycle = this.cpu.cycles;
+      }
+      value &= ~(FOC1A | FOC1B | PSR1);
+
+      if (prevGtccrHook) {
+        prevGtccrHook(value, oldValue, addr, mask);
+      } else {
+        cpu.data[GTCCR] = value;
+      }
+
+      this.updateCompConfig();
+      return true;
+    };
+
+    // TIFR/TIMSK are shared with Timer0 — chain with existing hooks
+    const prevTifrHook = cpu.writeHooks[TIFR] as CPUMemoryHook | undefined;
+    cpu.writeHooks[TIFR] = (value: number, oldValue: number, addr: number, mask: number) => {
+      if (prevTifrHook) {
+        prevTifrHook(value, oldValue, addr, mask);
+      } else {
+        cpu.data[TIFR] = value;
+      }
+      cpu.clearInterruptByFlag(this.OVF, value);
+      cpu.clearInterruptByFlag(this.OCFA, value);
+      cpu.clearInterruptByFlag(this.OCFB, value);
+      return true;
+    };
+
+    const prevTimskHook = cpu.writeHooks[TIMSK] as CPUMemoryHook | undefined;
+    cpu.writeHooks[TIMSK] = (value: number, oldValue: number, addr: number, mask: number) => {
+      if (prevTimskHook) {
+        prevTimskHook(value, oldValue, addr, mask);
+      }
+      cpu.updateInterruptEnable(this.OVF, value);
+      cpu.updateInterruptEnable(this.OCFA, value);
+      cpu.updateInterruptEnable(this.OCFB, value);
+    };
+  }
+
+  private get tccr1() {
+    return this.cpu.data[this.config.TCCR1];
+  }
+
+  private get gtccr() {
+    return this.cpu.data[this.config.GTCCR];
+  }
+
+  private get CS() {
+    return this.tccr1 & CS_MASK;
+  }
+
+  private get ctcMode() {
+    return !!(this.tccr1 & CTC1);
+  }
+
+  private get pwmA() {
+    return !!(this.tccr1 & PWM1A);
+  }
+
+  private get pwmB() {
+    return !!(this.gtccr & PWM1B_BIT);
+  }
+
+  private get comA(): number {
+    return (this.tccr1 >> 4) & 0x3;
+  }
+
+  private get comB(): number {
+    return (this.gtccr >> 4) & 0x3;
+  }
+
+  /** TOP = OCR1C in CTC/PWM modes, 0xFF in Normal mode */
+  private get TOP() {
+    if (this.ctcMode || this.pwmA || this.pwmB) {
+      return this.ocrC;
+    }
+    return 0xff;
+  }
+
+  count = (reschedule = true) => {
+    const { divider, lastCycle, cpu } = this;
+    const { cycles } = cpu;
+    const delta = cycles - lastCycle;
+
+    if (divider && delta >= divider) {
+      const counterDelta = Math.floor(delta / divider);
+      this.lastCycle += counterDelta * divider;
+      const val = this.tcnt;
+      const top = this.TOP;
+      const phasePwm = (this.pwmA || this.pwmB) && !this.ctcMode;
+
+      const newVal = phasePwm
+        ? this.phasePwmCount(val, counterDelta)
+        : (val + counterDelta) % (top + 1);
+      const overflow = val + counterDelta > top;
+
+      if (!this.tcntUpdated) {
+        this.tcnt = newVal;
+        if (!phasePwm) {
+          this.timerUpdated(newVal, val);
+        }
+      }
+
+      if (!phasePwm && overflow) {
+        cpu.setInterruptFlag(this.OVF);
+      }
+    }
+
+    if (this.tcntUpdated) {
+      this.tcnt = this.tcntNext;
+      this.tcntUpdated = false;
+    }
+
+    if (this.updateDivider) {
+      const cs = this.CS;
+      const newDivider = this.config.dividers[cs] ?? 0;
+      this.lastCycle = newDivider ? this.cpu.cycles : 0;
+      this.updateDivider = false;
+      this.divider = newDivider;
+      if (newDivider) {
+        cpu.addClockEvent(this.count, this.lastCycle + newDivider - cpu.cycles);
+      }
+      return;
+    }
+
+    if (reschedule && divider) {
+      cpu.addClockEvent(this.count, this.lastCycle + divider - cpu.cycles);
+    }
+  };
+
+  private phasePwmCount(value: number, delta: number): number {
+    const top = this.TOP;
+
+    while (delta > 0) {
+      if (this.countingUp) {
+        value++;
+        if (value >= top) {
+          value = top;
+          this.countingUp = false;
+        }
+      } else {
+        value--;
+        if (value <= 0) {
+          value = 0;
+          this.countingUp = true;
+          this.cpu.setInterruptFlag(this.OVF);
+        }
+      }
+
+      if (!this.tcntUpdated) {
+        if (value === this.ocrA) {
+          this.cpu.setInterruptFlag(this.OCFA);
+          this.updateCompPinPwm('A');
+        }
+        if (value === this.ocrB) {
+          this.cpu.setInterruptFlag(this.OCFB);
+          this.updateCompPinPwm('B');
+        }
+      }
+      delta--;
+    }
+    return value & 0xff;
+  }
+
+  private timerUpdated(value: number, prevValue: number) {
+    const { ocrA, ocrB } = this;
+    const overflow = prevValue > value;
+    if (((prevValue < ocrA || overflow) && value >= ocrA) || (prevValue < ocrA && overflow)) {
+      this.cpu.setInterruptFlag(this.OCFA);
+      if (this.comA && !this.pwmA) {
+        this.updateCompPinNonPwm('A');
+      }
+    }
+    if (((prevValue < ocrB || overflow) && value >= ocrB) || (prevValue < ocrB && overflow)) {
+      this.cpu.setInterruptFlag(this.OCFB);
+      if (this.comB && !this.pwmB) {
+        this.updateCompPinNonPwm('B');
+      }
+    }
+  }
+
+  private forceCompare(channel: 'A' | 'B') {
+    if (channel === 'A' && !this.pwmA && this.comA) {
+      this.updateCompPinNonPwm('A');
+    } else if (channel === 'B' && !this.pwmB && this.comB) {
+      this.updateCompPinNonPwm('B');
+    }
+  }
+
+  private updateCompPinNonPwm(channel: 'A' | 'B') {
+    const com = channel === 'A' ? this.comA : this.comB;
+    const pin = channel === 'A' ? this.config.compPinA : this.config.compPinB;
+    let mode: PinOverrideMode;
+    switch (com) {
+      case 1:
+        mode = PinOverrideMode.Toggle;
+        break;
+      case 2:
+        mode = PinOverrideMode.Clear;
+        break;
+      case 3:
+        mode = PinOverrideMode.Set;
+        break;
+      default:
+        return;
+    }
+    this.cpu.gpioByPort[this.config.compPortB]?.timerOverridePin(pin, mode);
+  }
+
+  private updateCompPinPwm(channel: 'A' | 'B') {
+    const com = channel === 'A' ? this.comA : this.comB;
+    const pin = channel === 'A' ? this.config.compPinA : this.config.compPinB;
+    const invertingMode = com === 3;
+    const isSet = this.countingUp === invertingMode;
+    let mode: PinOverrideMode;
+    switch (com) {
+      case 1:
+        mode = PinOverrideMode.Toggle;
+        break;
+      case 2:
+      case 3:
+        mode = isSet ? PinOverrideMode.Set : PinOverrideMode.Clear;
+        break;
+      default:
+        return;
+    }
+    this.cpu.gpioByPort[this.config.compPortB]?.timerOverridePin(pin, mode);
+  }
+
+  private updateCompConfig() {
+    const port = this.cpu.gpioByPort[this.config.compPortB];
+    if (!port) return;
+    port.timerOverridePin(
+      this.config.compPinA,
+      this.comA ? PinOverrideMode.Enable : PinOverrideMode.None,
+    );
+    port.timerOverridePin(
+      this.config.compPinB,
+      this.comB ? PinOverrideMode.Enable : PinOverrideMode.None,
+    );
+  }
+}