Knight Board Firmware

The NeuroPawn library provides the acquisition core as a precompiled Arduino library for the ATmega328P Knight Board. Your firmware owns the normal Arduino setup() and loop() functions while the library configures the EEG front-end, collects samples, emits binary frames, and services host commands.

For installation and upload instructions, start with Uploading Custom Firmware.

Firmware Lifecycle

#include <NeuroPawn.h>

void setup() {
  neuropawn.setup(NP_DEFAULT);
}

void loop() {
  neuropawn.acquire_data();
  // Run short, non-blocking application tasks here.
}

setup() starts serial at 115200 baud and configures the acquisition hardware. acquire_data() is non-blocking and sends one frame whenever a new sample is ready. It must run on every loop iteration.

API

Call	Purpose
`neuropawn.init_globals(mode)`	Reset internal state. Optional because `setup()` calls it automatically
`neuropawn.setup(mode)`	Initialize serial, EEG, and optional IMU; returns front-end readiness
`neuropawn.acquire_data(mode)`	Emit new samples and service host commands without blocking
`neuropawn.quiet(true)`	Suppress human-readable boot messages; call before `setup()`
`neuropawn.ready()`	Report whether the EEG front-end was detected and configured
`neuropawn.imu_present()`	Report whether the IMU responded on I2C
`neuropawn.mode()`	Return the configured mode
`neuropawn.frame_counter()`	Return the rolling 0-255 frame counter
`NeuroPawnBoard::pin_available(pin)`	Check whether a pin is available in the current mode

acquire_data() defaults to NP_AS_CONFIGURED, which reuses the mode passed to setup().

Modes

Mode	Frame size	Behavior
`NP_DEFAULT`	21 bytes	Eight EEG channels; I2C is not initialized and A4/A5 remain free
`NP_IMU`	57 bytes	EEG plus acceleration, gyroscope, and magnetometer data
`NP_AS_CONFIGURED`	-	Reuse the mode selected by `setup()`

NP_IMU also requires a firmware build compiled with NEUROPAWN_IMU. Without that build flag it behaves like NP_DEFAULT. When IMU support is compiled in but no sensor responds, the firmware preserves the 57-byte layout and fills the 36-byte IMU payload with zeroes.

See Knight Board Data Format for byte-level packet layouts and Creating a Custom Data Parser for a complete host parser.

Hardware Limits

The acquisition core owns the following resources. Do not reconfigure or drive them from application code.

Reserved pins

Pin	Use
D0, D1	USB serial data link
D3	EEG acquisition
D8-D13	EEG acquisition and SPI; D13 LED is not available
A4, A5	I2C in `NP_IMU` mode

Available pins

Pin	Capability
D2	Digital I/O and INT0
D4	Digital I/O
D5, D6	Digital I/O and Timer0 PWM
D7	Digital I/O
A0-A3	Analog input or digital I/O
A6, A7	Analog input only
A4, A5	Available only in `NP_DEFAULT`

Call NeuroPawnBoard::pin_available(pin) before configuring a pin whose availability depends on the selected mode.

Shared resources

Resource	Constraint
Serial	Library-owned binary link; never write application text to it
SPI	Library-owned; do not attach another SPI device
I2C	May be shared in IMU mode except at IMU addresses `0x68` and `0x69`
Timer0	Used by `millis()`, `micros()`, and `delay()`; do not reprogram it
Timer1, Timer2	Available, although Arduino `tone()` uses Timer2
RAM	About 280 B for EEG-only or 920 B for an IMU build, out of 2048 B
Flash	About 7.5 kB for EEG-only or 21 kB for an IMU build, out of 30.7 kB

Host Control

After startup, all EEG channels are powered down and the right-leg-drive (RLD) derivation is empty. acquire_data() listens for ASCII commands on the same serial link to enable channels, choose gains, and configure RLD. The binary stream continues around those commands.

See the Command Set for supported commands and the custom firmware guide for the timing and serial rules application code must follow.