Abraham Board Code

Abraham is the SD logging board. It receives framed telemetry over I2C, validates and reassembles fixed 98-byte packets, then writes raw packets to SD while logging operational events to a text log.

What This Firmware Does

• Listens for framed I2C traffic and queues frames from ISR context.
• Accepts only SD-destination frames (header bit0).
• Validates payload checksum and start/continuation ordering.
• Reassembles exactly 98 bytes, then appends packet to binary log file.
• Writes diagnostic entries to rolling text log.

End-to-End Receive/Log Flow

Wire.onReceive ISR
   |
   v
Frame queue (size 8)
   |
   v
processI2CFrame:
  - header length check
  - destination SD filter
  - checksum verify
  - packet assembly state machine
   |
   v
on 98 bytes complete -> writeTelemetryPacket() -> current-data.bin
                          +
                          appendLog() -> current-log.txt

Framing and Packet Parameters

Item	Value
Telemetry packet size	98 bytes
I2C max frame size	32 bytes
I2C header size	2 bytes
I2C payload per frame	up to 30 bytes
Packet assembly timeout	1000 ms
Frame queue size	8
SD destination flag	byte0 bit0
Start flag	byte0 bit7
Checksum byte	byte1 (sum of payload bytes)

SD File Behavior

At boot:

1. Existing current-log.txt and current-data.bin are rotated to numbered archive names when possible.
2. Fresh current-log.txt and current-data.bin are created.
3. Runtime status entries are appended to the log.

During operation:

• Valid packet writes append exactly 98 bytes to current-data.bin.
• Invalid conditions (checksum failure, overflow, timeout, short frame, queue overflow) are counted and logged.

Validation and Failure Handling

Condition	Action
Frame shorter than header	Drop frame and discard partial packet
Destination bit0 not set	Ignore frame
Checksum mismatch	Increment checksum failure counter and discard partial
Continuation without active packet	Drop continuation
Buffer overflow risk	Discard partial packet
Timeout before 98 bytes	Discard partial packet
Queue overflow	Increment dropped frame counter and discard partial packet

Related Tooling

• Spencer repo includes telemetry_packet_viewer.py, which decodes the same 98-byte packet format written by Abraham to current-data.bin.

Debug guide

Status LEDs

This firmware does not drive a status LED. There is no on-board blink pattern for I2C or SD activity.

UART / serial

This firmware does not call Serial or Serial1. Runtime diagnostics go to the SD card:

• current-log.txt — human-readable timestamps (millis()), I2C/assembly errors, write results, queue overflows.
• current-data.bin — raw length-prefixed telemetry records (same layout as TelemetryData on the wire).

If you add Serial1 logging on a Teensy, use a 3.3 V USB–UART adapter:

• GND — common ground with the Teensy
• Adapter RX → Teensy TX1 (pin 1)
• Adapter TX → Teensy RX1 (pin 0)

Use 115200 baud unless you change it in code. Do not use 5 V TTL on Teensy pins.

I2C

Abraham listens as I2C slave 0x09 and only accepts frames with the SD destination bit set (header byte 0 bit 0). See AbrahamBoardCode.ino for framing constants.