Nicolai nbuchwitz

The Raspberry Pi foundation have now released a beta version of an official 64-bit Kernel which can be installed using the rpi-update script. The rpi-update script can be found at https://github.com/Hexxeh/rpi-update/blob/master/rpi-update or through the Raspbian repositories.

Introduction

The objective of these instructions is to build a stock 64bit Linux Kernel for use on the Raspberry Pi 3B on a Debian x64 machine (Windows Subsystem for Linux in my case), and deploy on the Raspberry Pi.

Notes:

Transfer to Pi is using my NAS in this example, replace with shared drive/memory stick etc. as required.
- (N: drive on Windows and /mnt/NAS on Linux in this example).
For a specific Kernel version replace the 4.19 with the wanted version in the git clone command.

New location

Head over to https://github.com/waja/debian-update-cheatsheets/blob/stretch2buster/stretch2buster.sh

Controlling the Brother P-Touch Cube label maker from a computer

The Brother PTP300BT label maker is intended to be controlled using the official Brother P-Touch Design & Print iOS/Android app. The app has arbitrary limits on what you can print (1 text object and up to 3 preset icons), so I thought it would be a fun challenge to reverse engineer the protocol to print whatever I wanted.

Python code at the bottom if you want to skip the fine details.

Process

Intitially I had a quick peek at the Android APK to see if there was any useful information inside. The code that handles the communication with the printer in Print&Design turned out to be a native library, but the app clearly prepares a bitmap image and passes it to this native library for printing. Bitmaps are definitely something we can work with.

	/* ext2scan:
	* Scans an input stream, sector by sector, for something that looks like an ext{2,3,4} partition.
	* It does this by looking for a magic WORD, 0xEF53, at a known offset into the sector.
	* For random data, this will occur by chance around once per 32MB of data, so we also
	* check whether the first two sectors are all zeros, which is commonly true for ext partitions.
	*
	* Compile with:
	* gcc ./ext2scan.c -o ./ext2scan
	*
	* Example usage:

	#!/usr/bin/env sh

	# Generate an AUTHORS file based on the output of git shortlog. It uses ABC
	# order, strips out leading spaces and numbers, then filters out specific
	# authors.

	git shortlog -se \
	\| perl -spe 's/^\s+\d+\s+//' \
	\| sed -e '/^CommitSyncScript.*$/d' \
	> AUTHORS

	- install the two shellscripts into the appropriate places under /etc/initramfs-tools
	- run update-initramfs
	- put "overlay=yes" on the kernel command line
	- reboot

	With the overlay in place, the real root is mounted readonly on /ro.
	Only the root fs is changed, other filesystems are mounted normally.

	Remove "overlay=yes" (or change it to something other than yes) and reboot to go back to readwrite.
	(This probably means that you want the commandline config to live somewhere other than on the root fs, e.g. under /boot)

	# Assumptions: easyrsa3 available in current dir, and functional openssl.
	# This basic example puts the "offline" and "sub" PKI dirs on the same system.
	# A real-world setup would use different systems and transport the public components.

	# Build root CA:
	EASYRSA_PKI=offline ./easyrsa init-pki
	EASYRSA_PKI=offline ./easyrsa build-ca nopass

	# Build sub-CA request:
	EASYRSA_PKI=sub ./easyrsa init-pki