Rasberry Pi

Device

• Rasberry Pi 3B ("Rev 1.2")

cat /proc/device-tree/model

Hardware info:

• AV Connector:
  • 1 (tip): L Audio
  • 2: R Audio
  • 3: Ground
  • Sleeve: Composite Video.
• Boards
• GPIO Header
  • 3.3 V on data lines only
  • Pin numbers differ from chip/programmatic pin numbers
  • 3.3 V power lines: 150-200 mA max
  • 5 V power lines: from the main PSU input (reserve 1 A for Pi itself)
  • Data lines: 15 mA max per pin, 50 mA total from all pins

Rasbery Pi OS

See /boot/firmware/config.txt.

Command line configuration program:

raspi-config

eg to enable I2C interface.

Upgrade:

apt update
apt list --upgradeable
apt upgrade -y

Apache Web Server

apt install apache2 -y

• Configuration: /etc/apache2
• Serve from: /var/www/html

Composite Video

Will default to NTSC; in /boot/firmware/cmdline.txt, add this to the end for PAL 50i:

video=Composite-1:720x576@50ie

Alternatives include:

* NTSC: 720x480@60ie
* PAL60: 720x480@60ie

This will show the Pi desktop. Stop it to allow direct access to the framebuffer /dev/fb0:

systemctl stop lightdm

See also:

raspi-config

• 1 System Options -> S5 Boot / Auto Login -> B1 Console

Can explicitly set the standard:

video=Composite-1:720x576@50ie,tv_mode=PAL

Alternatives:

• PAL / PAL-M / PAL-N
• NTSC / NTSC-J (Japan) / NTSC-443
• SECAM

To avoid overscan on TVs, add padding:

video=Composite-1:720x576@50ie,margin_left=48,margin_right=48,margin_top=12,margin_bottom=12

Go Development

Because of limited RAM, best to cross compile on a more powerful system:

CGO_ENABLED=0 GOOS=linux GOARCH=arm GOARM=7 go build myprog.go

Or install ARMv6 release:

wget https://go.dev/dl/go1.26.3.linux-armv6l.tar.gz
tar -C /usr/local -xzf go1.26.3.linux-armv6l.tar.gz

Set environment variables:

PATH=$PATH:/usr/local/go/bin
GOPATH=$HOME/go

GPIO Development

Raspberry Pi OS use the newer gpiod subsystem (which interacts with /dev/gpiochip0).

In C++:

apt install libgpiod-dev gpiod -y
g++ -O3 prog.cpp -o prog -lgpiodcxx

See documentation.

In Python, use:

apt install python3-dev -y

for python gpiod bindings. See documentation.

Or the abstraction:

apt install python3-gpiozero -y

In Go, use: periph.io

I2C Development

Check devices:

i2cdetect -y 1

Get a byte (BME280/BMP280 chip ID register 0xD0):

i2cget -y 1 0x76 0xD0

This returns 0x60 for BME280, 0x58 for BMP280)

In C++:

apt install libi2c-dev
g++ i2c_prog.cpp -o i2c_prog -li2c

Mail

MUA:

apt install bsd-mailx
apt install mutt

Mount mail directory from server:

mailhost:/var/spool/mail    /var/mail    nfs    rw,nofail,noatime,_netdev,soft    0    0

Or use automounter (see other section). Note: UID/GID must match.

Exim is the default MTA:

dpkg-reconfigure exim4-config
update-exim4.conf
systemctl restart exim4

Monitor logs:

tail -f /var/log/exim4/mainlog

NFS Automounter

apt install autofs nfs-common -y

To allow remove mounts to be accessed under /net/<server>/<export>, edit /etc/auto.master and enable the host map:

/net    -hosts --timeout=60

systemctl enable autofs
systemctl restart autofs

To mount remote mail directory:

Create the new /etc/auto.master.d/mail.autofs file:

/-    /etc/auto.direct    --timeout=60

Create the /etc/auto.direct file:

/var/mail    -fstype=nfs,rw,soft,tcp,rsize=8192,wsize=8192    mailhost:/var/spool/mail

systemctl restart autofs

NTP Client

apt install systemd-timesyncd -y

Edit /etc/systemd/timesyncd.conf and set NTP parameter

systemctl restart systemd-timesyncd
timedatectl status
timedatectl timesync-status

Service

Create a service file /etc/systemd/system/temp-logger.service:

[Unit]
Description=CPU Temperature Logger to HTML
After=network.target

[Service]
Type=oneshot
ExecStart=/usr/local/bin/temp_logger.sh
# Run as root or www-data depending on who owns your /var/www/html directory
User=root

Create a systemd timer /etc/systemd/system/temp-logger.timer:

[Unit]
Description=Run Pi Temperature Logger every 5 minutes

[Timer]
# Run 5 minutes after boot-up
OnBootSec=5min
# Run every 5 minutes relative to when the timer was started
OnUnitActiveSec=5min
# Ensures precision alignment to the clock wall if desired (optional)
AccuracySec=1s

[Install]
WantedBy=timers.target

Reload systemd,

systemctl daemon-reload
systemctl enable --now temp-logger.timer

SSH

Copy key (and generate ~/.ssh) from client tp pi:

ssh-copy-id [email protected]

Stress

apt install stress-ng

Run memory test:

stress-ng --vm 1 --vm-bytes 750M --timeout 120 --vm-keep --vm-method rand-sum

CPU test:

stress-ng --cpu 4 --cpu-method matrixprod --timeout 300

Swap

free -m
swapon --show

To see current zram configuration:

zramctl 
zramctl --output-all /dev/zram0

Configure hybrid configuration, overruding default /etc/rpi/swap.conf in /etc/rpi/swap.conf.d/hybrid-swap.conf:

[Main]
Mechanism=zram+file

[Zram]
FixedSizeMiB=512

[File]
FixedSizeMiB=1024

Ensure systemd component is enabled and reboot:

systemctl enable var-swap.swap

There is no need to recreate/resize the /var/swap physical file, which is done at boot time if necessary. In this mode, file system swap will not be visible with swapon; instead it is owned by the zram kernel driver. Zram blocks are pushed to/from file as needed.

Temperature

echo "scale=2; $(cat /sys/class/thermal/thermal_zone0/temp) / 1000" | bc

CPU Core throttling above 80 C.

Wifi

Turn off wifi:

nmcli radio wifi off