RAK6421 Pi HAT EEPROM Flashing Guide

This guide explains how to write the HAT EEPROM on a RAK6421 Pi HAT and verify that it was written correctly.

What Is Raspberry Pi HAT+?

HAT means Hardware Attached on Top. A Raspberry Pi HAT/HAT+ is an add-on board that can identify itself to the Pi through an EEPROM (usually at I2C address 0x50).

When EEPROM data is valid, Raspberry Pi OS can read details such as:

Vendor and product name
Product ID and version
Custom fields (for example hardware version or slot/module mapping)

Those values appear under /proc/device-tree/hat/.

IMPORTANT

Power off first before changing any jumper/short.
You must short the EEPROM write-enable pins on the RAK6421 to allow writing.
If write-enable is not shorted, the flash command can look successful but the EEPROM content is not actually updated.
After flashing, remove the short again if you want normal write protection behavior.

Prerequisites

Raspberry Pi OS running on the target Pi.
Basic terminal access (ssh or local terminal).
Required commands available: eepmake, eepflash.sh, eepdump, i2cdetect, python3.
This repository cloned on the Pi.

Quick check:

which eepmake eepflash.sh eepdump i2cdetect python3

Flashing Steps

1. Enable I2C Bus 0 (Required)

The HAT EEPROM is on I2C bus 0. If bus 0 is not enabled, the EEPROM at 0x50 will not be detected.

Edit the Raspberry Pi config and make sure these lines are present in /boot/firmware/config.txt:

dtparam=i2c_vc=on
dtoverlay=i2c0

Then reboot:

sudo reboot

2. Confirm EEPROM Is Visible at 0x50

After reboot:

i2cdetect -y 0

Expected output includes 50 in the 0x50 row, similar to:

1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
                         -- -- -- -- -- -- -- --
 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 -- -- -- -- -- -- -- --

If 0x50 is missing, fix I2C config first before flashing.

3. Prepare EEPROM Content File

Edit RAK-6421-eeprom.txt for your board:

product_id, product_ver, vendor, product
custom_data lines such as:

custom_data "hardware_version D"
custom_data "io_slot1 RAK13302"

NOTE

Use format custom_data "field value" (space separator, no colon).
Keep comments starting with #.
Keep product_uuid as all zeroes if you want eepmake to auto-generate a UUID.

4. Enable Write (Hardware Short)

Before writing EEPROM:

Power off the Pi.
Short the EEPROM write-enable pins on the RAK6421.
Power on the Pi.

Figure 1: Short on the EEPROM Enable Pins

Do not skip this step.

5. Flash + Verify (Recommended Script)

Run from repository root:

python3 flash-eeprom-and-check.py

You can also pass a sudo password as an argument:

python3 flash-eeprom-and-check.py '<sudo-password>'

The script performs:

eepmake RAK-6421-eeprom.txt RAK-6421-eeprom.eep
eepflash.sh -y -w -f=RAK-6421-eeprom.eep -t=24c32
Read-back + parse verification against the config file
JSON result output with PASS/FAIL status per field

You can also pass sudo password as argument:

python3 flash-eeprom-and-check.py '<sudo-password>'

Manual Flashing (Without the Script)

If you prefer to run the commands yourself instead of using flash-eeprom-and-check.py, follow these steps. The same prerequisites apply (I2C bus 0 enabled, write-enable pins shorted, etc.).

1. Generate the Binary EEPROM File

Use eepmake to convert your text config into a binary .eep file:

eepmake RAK-6421-eeprom.txt RAK-6421-eeprom.eep

If you use a different config file or output name:

eepmake <your-config>.txt <output>.eep

2. Write to the EEPROM

Use eepflash.sh to write the binary image. The RAK6421 uses a 24c32 EEPROM:

sudo eepflash.sh -y -w -f=RAK-6421-eeprom.eep -t=24c32

Flag	Description
`-y`	Skips confirmation prompts
`-w`	Write mode (use `-r` for read)
`-f=`	Specifies the file
`-t=24c32`	Specifies the EEPROM type

3. (Optional) Read Back and Verify

To manually verify what was written:

# Read EEPROM to a file
sudo eepflash.sh -y -r -f=verify.eep -t=24c32

# Dump binary to human-readable text
eepdump verify.eep verify.txt

# Inspect the result
cat verify.txt

Then compare verify.txt with your RAK-6421-eeprom.txt to confirm the values match.

4. Reboot and Check Device-Tree

Reboot the Pi, then inspect what the OS sees:

cat /proc/device-tree/hat/
cat /proc/device-tree/hat/custom_0
cat /proc/device-tree/hat/custom_1

Troubleshooting Checklist

i2cdetect -y 0 does not show 50

Confirm dtparam=i2c_vc=on and dtoverlay=i2c0 are in config.
Reboot and test again.

Flash command reports success but values do not change

Write-enable pins were not shorted (most common issue).

Verification mismatch in script output

Check custom_data formatting and spelling in RAK-6421-eeprom.txt.
Reflash with write-enable short in place.