paravr - Parallel Port AVR Programmer

A simple, dependency-free AVR ISP programmer for Linux using a real parallel port. Supports both onboard LPT ports and PCI/PCIe parallel port cards.

Features

• Zero dependencies - Uses only Python standard library and Linux ppdev
• Auto-detection - Automatically finds the correct configuration for your hardware
• PCI card support - Works with add-in parallel port cards (which often have non-standard behavior)
• Configuration saving - Saves working config so you don't need to specify options every time
• Intel HEX support - Programs standard .hex files from Arduino IDE, avr-gcc, etc.

Requirements

• Linux with the ppdev kernel module
• A real parallel port (USB-to-parallel adapters will NOT work)
• Python 3.7+
• Root access (or appropriate permissions for /dev/parport0)

Wiring

Connect your parallel port to the AVR's ISP header:

DB-25 Parallel Port          AVR / Arduino Uno
───────────────────          ─────────────────
Pin 2  (D0)           →      MOSI  (Arduino pin 11)
Pin 3  (D1)           →      SCK   (Arduino pin 13)
Pin 4  (D2)           →      RESET (Arduino RESET pin)
Pin 10 (ACK/S6)       ←      MISO  (Arduino pin 12)
Pin 18-25 (GND)       →      GND

      DB-25 Female                ICSP Header
    (directly on cable)          (on Arduino)
                              
    13 12 11 10  9  8  7         MISO ● ○ VCC
     ○  ○  ○  ○  ○  ○  ○          SCK ○ ○ MOSI
                                RESET ○ ○ GND
    25 24 23 22 21 20 19 18
     ○  ○  ○  ○  ○  ○  ○  ○
           (all GND)
     
     1  2  3  4  5  6  7  8
     ○  ●  ●  ●  ○  ○  ○  ○
        │  │  │
        │  │  └── RESET (D2)
        │  └───── SCK   (D1)
        └──────── MOSI  (D0)

Making a Cable

You'll need:

• DB-25 male connector (or female if connecting to extension cable)
• 5 wires (4 signal + ground)
• 2x3 pin header for ICSP, or individual Dupont wires

Connections:

DB-25 Pin	Signal	AVR Pin	Arduino Uno
2	MOSI	MOSI	Pin 11
3	SCK	SCK	Pin 13
4	RESET	RESET	RESET
10	MISO	MISO	Pin 12
18-25	GND	GND	GND

Quick Start

1. Load the ppdev module

sudo modprobe ppdev

To load automatically on boot, add to /etc/modules-load.d/ppdev.conf:

ppdev

2. Auto-detect your configuration

sudo python3 paravr.py --detect

This tests various configurations and saves the working one.

3. Program your AVR

sudo python3 paravr.py --hex firmware.hex

Usage

Auto-Detection (First Time Setup)

sudo python3 paravr.py --detect

This will:

1. Test all MISO pin configurations
2. Test various speeds
3. Find and save the working configuration

Programming

# Program with auto-detected config
sudo python3 paravr.py --hex firmware.hex

# Program a specific MCU (default is ATmega328P)
sudo python3 paravr.py --hex firmware.hex --mcu m168p

# Skip verification (faster but less safe)
sudo python3 paravr.py --hex firmware.hex --no-verify

# Force program even if signature doesn't match
sudo python3 paravr.py --hex firmware.hex --force

Reading Fuses

sudo python3 paravr.py --fuses

Testing the Parallel Port

sudo python3 paravr.py --test

This toggles the output pins - watch for the SCK LED (pin 13) blinking on Arduino.

Manual Configuration

If auto-detect doesn't work, you can specify options manually:

# Standard onboard parallel port
sudo python3 paravr.py --hex firmware.hex --miso 10

# PCI parallel port card (no STATUS inversion)
sudo python3 paravr.py --hex firmware.hex --miso 100

# With slower speed
sudo python3 paravr.py --hex firmware.hex --miso 100 --speed 500

List Options

# List supported MCUs
sudo python3 paravr.py --list-mcus

# List MISO configurations  
sudo python3 paravr.py --list-miso

MISO Configurations

Different parallel ports map the MISO input differently:

ID	Description	Use When
10	Pin 10, inverted	Standard onboard LPT ports
100	Pin 10, not inverted	Most PCI/PCIe parallel cards
11	Pin 11, inverted	MISO wired to BUSY pin
101	Pin 11, not inverted	PCI card with MISO on BUSY

Run --detect to automatically find the correct one.

Supported MCUs

ID	Name	Flash	EEPROM
m328p	ATmega328P	32K	1K
m328	ATmega328	32K	1K
m168p	ATmega168P	16K	512
m168	ATmega168	16K	512
m88p	ATmega88P	8K	512
m88	ATmega88	8K	512
m48p	ATmega48P	4K	256
m48	ATmega48	4K	256
m2560	ATmega2560	256K	4K
m1280	ATmega1280	128K	4K
m32u4	ATmega32U4	32K	1K
t85	ATtiny85	8K	512
t45	ATtiny45	4K	256
t25	ATtiny25	2K	128
t84	ATtiny84	8K	512
t44	ATtiny44	4K	256
t24	ATtiny24	2K	128
t2313	ATtiny2313	2K	128

Troubleshooting

"Permission denied for /dev/parport0"

Run with sudo, or add yourself to the lp group:

sudo usermod -a -G lp $USER
# Log out and back in

"/dev/parport0 not found"

Load the ppdev module:

sudo modprobe ppdev

"Failed to enter programming mode"

1. Check power - Is the Arduino/AVR powered? (USB connected)
2. Check ground - GND must be connected (DB-25 pins 18-25)
3. Check wiring - Verify all 4 signal wires are correct
4. Try slower speed - --speed 500 or --speed 1000
5. Run --detect - Let it find the correct configuration

"No working configuration found"

• Verify wiring with a multimeter
• Make sure the AVR has a working clock (external crystal or internal)
• Try pressing the reset button on Arduino while running --detect
• Check that you're using a REAL parallel port (USB adapters don't work)

PCI Parallel Port Cards

Many PCI/PCIe parallel port cards don't implement hardware inversion on STATUS bits. Run --detect which will try both inverted and non-inverted configurations.

Common cards that work:

• Asix AX99100 based cards
• MosChip MCS9900 based cards
• Most "native" PCIe parallel cards

Getting .hex Files

From Arduino IDE

1. Open your sketch
2. Sketch → Export compiled Binary
3. Find the .hex file in your sketch folder

From avr-gcc

avr-gcc -mmcu=atmega328p -o firmware.elf firmware.c
avr-objcopy -O ihex firmware.elf firmware.hex

From PlatformIO

pio run
# .hex file is in .pio/build/*/firmware.hex

Configuration File

Auto-detected settings are saved to:

~/.config/paravr/config.json

Format:

{
  "/dev/parport0": {
    "miso_config": 100,
    "speed_us": 100,
    "invert_reset": false
  }
}

How It Works

This programmer uses "bit-banging" - directly controlling the parallel port's DATA pins to generate the SPI signals (MOSI, SCK, RESET) and reading the STATUS register for MISO.

The parallel port is accessed via Linux's ppdev interface, which provides user-space access to the port's registers through ioctl calls.

Why USB Adapters Don't Work

USB-to-parallel adapters only implement the printer protocol, not direct register access. They can't bit-bang SPI signals fast enough or read inputs in real-time.

License

MIT License - See source file for details.