105 lines
4.1 KiB
Markdown
105 lines
4.1 KiB
Markdown
# Raspberry Pi 1 Bare-Metal Synthesizer
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This project turns an original Raspberry Pi (Model 1 B/B+, Zero, or Zero W) into an instant-on, single-voice synthesizer that runs without any operating system (bare metal).
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It boots in under two seconds and produces sound and graphics with minimal external components.
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## Features
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- **Instant-On**: Boots directly into the synth application in ~1-2 seconds.
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- **Audio Output**: Generates a sawtooth waveform on the 3.5mm composite audio jack.
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- **Video Output**: Displays a simple amplitude visualizer on the composite video output.
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- **Looped Melody**: Plays a pre-programmed random melody, no input required.
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## Requirements
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### Hardware
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- **Raspberry Pi**: Model 1 (A, B, B+), Pi Zero, or Pi Zero W. This code is for the **BCM2835** SoC and will **not** work on Pi 2, 3, 4, or 5.
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- **SD Card**: A microSD or standard SD card (depending on your Pi model), 1GB is more than enough.
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- **Power Supply**: A standard 5V micro-USB power supply.
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- **Audio Cable**: A 3.5mm audio cable to connect to headphones or a speaker.
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### Software
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- **ARM Cross-Compiler**: The `arm-none-eabi-gcc` toolchain is required to build the kernel.
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- **Raspberry Pi Firmware**: You need the `bootcode.bin` and `start.elf` files from the official Raspberry Pi firmware repository.
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## Quick Start with Scripts
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For a fast and easy setup, you can use the provided automation scripts.
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1. **Build the kernel**:
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```sh
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./build.sh
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```
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This will compile the C and Assembly code and create the `kernel.img` file.
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2. **Deploy to SD Card**:
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Insert your FAT32-formatted SD card. Find its device name (e.g., `/dev/sdX` or `/dev/mmcblkX`) and mount point.
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```sh
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# Example: ./deploy.sh /media/user/RASPIBOOT
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./deploy.sh <path_to_sd_card_mount_point>
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```
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This script copies `kernel.img`, `bootcode.bin`, and `start.elf` to the SD card and then safely unmounts it.
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## Manual Setup and Deployment
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### 1. Install Toolchain
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On Debian/Ubuntu-based systems, you can install the cross-compiler with:
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```sh
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sudo apt-get update
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sudo apt-get install gcc-arm-none-eabi binutils-arm-none-eabi
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```
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### 2. Get Raspberry Pi Firmware
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The Pi's GPU first loads firmware from the SD card before handing control to the ARM core. You need two files:
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- `bootcode.bin`: The second-stage bootloader.
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- `start.elf`: The GPU firmware.
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You can download them from the official Raspberry Pi firmware repository. Make sure to grab the files from the `boot` directory. For this project, you only need these two files.
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Place them in the root of this project directory so the `deploy.sh` script can find them.
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### 3. Build the Kernel
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With the toolchain installed, compile the synthesizer by running `make`:
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```sh
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make
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```
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This command uses the `Makefile` to compile `boot.S` and `kernel.c`, linking them into a final binary image named `kernel.img`.
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### 4. Prepare the SD Card
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Your SD card must be formatted with a **FAT32** filesystem. Most new SD cards are already formatted this way. The partition should also have the "boot" or "lba" flag set, which is standard for bootable Raspberry Pi cards.
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### 5. Deploy to SD Card
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Mount the SD card and copy the three essential files to its root directory:
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- `bootcode.bin` (from the firmware repo)
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- `start.elf` (from the firmware repo)
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- `kernel.img` (generated by the `make` command)
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After copying, unmount the SD card safely.
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## Hardware Connections
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1. **SD Card**: Insert the prepared SD card into your Raspberry Pi.
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2. **Audio**: Connect headphones or a speaker to the 3.5mm audio jack.
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3. **Video (Optional)**: Connect a composite video cable from the RCA jack (on Model B) or the 3.5mm jack (on later models) to a compatible display.
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4. **Power**: Connect the 5V micro-USB power supply. The Pi will boot immediately.
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## Usage
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Once powered on, the synthesizer will automatically start playing a random melody loop. The composite video output will show a simple red bar that visualizes the audio amplitude.
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There is no user input required for this version of the code.
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---
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*This project is for educational purposes and demonstrates low-level hardware control on the BCM2835 SoC.* |