Exams/AdvOpsys/notes/work-summary-2026-04-15-v2.md

Assignment 5

#Overview

This assignment implements a simple music player using the PC speaker (PCSPK) and the Programmable Interval Timer (PIT). Songs are played by generating frequencies and controlling timing between notes.

---

#HowItWorks

#PCSpeaker

The PC speaker is controlled through port 0x61:

• Bits 0 and 1 enable/disable sound output

---

#PIT

The PIT is used for:

#SoundGeneration

• Channel 2 generates square wave audio
• Frequency is set using:

divisor = PIT_BASE_FREQ / frequency

#Timing

• Channel 0 runs at ~1000 Hz
• A tick counter is incremented via interrupts
• SleepInterrupt() is used for accurate note timing

---

#Implementation

#Playback

Each note contains:

• Frequency (Hz)
• Duration (ms)

Playback works by:

1. Setting frequency with PlaySound()
2. Waiting using SleepInterrupt()
3. Stopping sound with StopSound()

Rests are handled using R = 0.

---

#Challenges

#Timing

Busy-wait delays caused incorrect timing. This was solved by using interrupt-based sleeping.

#QEMU

QEMU has limited PC speaker support:

• Fast note changes sound unclear
• Songs degrade at high speed

---

#Adjustments

To improve playback clarity:

duration = original_duration * 2

This slows down the songs and makes notes more distinguishable.

---

#Conclusion

The system successfully:

• Generates sound using the PC speaker
• Uses PIT for timing and frequency control
• Plays songs with multiple notes

Limitations in QEMU affect sound quality, but the implementation itself works as intended.