florian.berthold
64f9e34fc3
Complete working firmware including: - CMakeLists.txt for Pico SDK build - SSD1306 OLED driver (128x32, I2C) - High-resolution latency measurement using hardware timer - Debounced button with short/long press detection - Three modes: Single, Continuous, Stats - USB serial debugging output Includes 8x8 font with numbers and letters for display.
115 lines
2.9 KiB
Markdown
115 lines
2.9 KiB
Markdown
# SN-L00 Firmware
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RP2040-based firmware for the SN-L00 Eurorack latency tester.
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## Requirements
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- [Raspberry Pi Pico SDK](https://github.com/raspberrypi/pico-sdk) v1.5+
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- CMake 3.13+
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- ARM GCC toolchain (`arm-none-eabi-gcc`)
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## Building
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### Linux/macOS
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```bash
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# Set SDK path (add to .bashrc/.zshrc for persistence)
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export PICO_SDK_PATH=/path/to/pico-sdk
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# Build
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cd firmware
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mkdir build && cd build
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cmake ..
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make
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```
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### Output files
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After building:
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- `sn_l00.uf2` - Flash via USB (drag to RPI-RP2 drive)
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- `sn_l00.elf` - For debugging with SWD
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## Flashing
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1. Hold BOOTSEL button on RP2040-Zero
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2. Connect USB cable (or press reset while holding BOOTSEL)
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3. Drag `sn_l00.uf2` to the `RPI-RP2` drive
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4. Module reboots automatically
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## Usage
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### Modes
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| Mode | Entry | Display | Behavior |
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|------|-------|---------|----------|
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| Single | Default / Long press from Continuous | `SINGLE` | Press button to measure once |
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| Continuous | Long press from Single | `CONT` | Auto-measures every 500ms |
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| Stats | Short press from Continuous | Min/Max/Avg | Shows measurement statistics |
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### Controls
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- **Short press**: Trigger measurement (Single mode) / Exit to Stats (Continuous)
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- **Long press (>500ms)**: Toggle between Single and Continuous modes
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- **Any press in Stats**: Return to Single mode, reset statistics
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## USB Serial
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The firmware exposes USB CDC serial for debugging:
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- Baud: 115200 (or any, it's USB CDC)
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- Shows measurement results and mode changes
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```bash
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# Linux
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screen /dev/ttyACM0 115200
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# macOS
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screen /dev/tty.usbmodem* 115200
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```
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## GPIO Pinout
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| GPIO | Function | Direction |
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|------|----------|-----------|
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| GP0 | I2C SDA (OLED) | Bidir |
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| GP1 | I2C SCL (OLED) | Output |
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| GP2 | Trigger Output | Output |
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| GP3 | Return Input | Input |
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| GP4 | Button | Input (pull-up) |
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## Code Structure
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```
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firmware/
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├── CMakeLists.txt # Build configuration
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├── include/
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│ ├── config.h # Pin definitions, timing constants
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│ ├── display.h # OLED display interface
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│ ├── latency.h # Measurement functions
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│ └── button.h # Button handling
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└── src/
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├── main.c # Application entry, state machine
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├── display.c # SSD1306 OLED driver
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├── latency.c # Timer-based latency measurement
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└── button.c # Debounced button with long press
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```
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## Measurement Accuracy
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- Timer resolution: ~1µs (RP2040 @ 125MHz)
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- Display resolution: 0.01ms (10µs)
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- Polling loop: ~1-2µs per iteration
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- Practical accuracy: ±10µs
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The main latency contributors are:
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1. Input buffer propagation delay (~10ns, negligible)
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2. GPIO read latency (~10ns, negligible)
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3. Polling loop timing (~1-2µs)
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## Future Improvements
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- [ ] Configurable trigger pulse width
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- [ ] Sample rate display (in samples @ 44.1/48/96kHz)
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- [ ] CV output proportional to latency
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- [ ] Threshold adjustment via long button hold
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- [ ] EEPROM settings storage
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