Raspberry Pi & Pico

Hardware
Electronics
Embedded
Published

March 21, 2018

Modified

December 31, 2022

Install

Official images…Raspberry Pi OS…

Write the image to an SD-card…

# or write the image to SD card
unzip -p $archive \
        | sudo dd status=progress conv=fsync bs=4M of=/dev/mmcblkX

Or use etcher to create bootable SD/USB devices.

Alternatives…

BuildRoot

Build your own images with:

Use a virtual machine as build environment:

# install depenencies
sudo apt install -y \
        bc \
        build-essential \
        cpio \
        file \
        git \
        libncurses5-dev \
        qemu-system-x86 \
        rsync \
        screen \
        unzip \
        wget \
# get the BuildRoot source code
git clone git://git.busybox.net/buildroot
# or
git clone https://github.com/buildroot/buildroot.git
# list available boards
make list-defconfigs | grep rasp
# generate the configuration for the target hardware
make raspberrypi0w_defconfig
# customization
make menuconfig    # search with `/`
# build
make
# write the SD card image
sudo dd bs=1M status=progress conv=fsync \
        if=output/images/sdcard.img of=/dev/mmcblkX

For debugging/testing it may be more convenient to use a:

# virtual machine configuration
make qemu_x86_64_defconfig
...
# launch the root-filesystem in a virtual machine
output/host/bin/qemu-system-x86_64 -M pc \
        -kernel output/images/bzImage \
        -drive file=output/images/rootfs.ext2,if=virtio,format=raw \
        -append "rootwait root=/dev/vda" \
        -net nic,model=virtio -net user

Directory structure:

host/           Built for the host, sysroot of the target toolchain
board/          Files and scripts to support each target board
configs/    Build configurations such as raspberrypi0w_defconfig
package/    Package definitions
output/host/    Build tools that run on the workstation
output/target/  Target output directory where target binaries are staged
output/images/  Filesystem images and the final firmware image are emitted here

USB Boot

Raspberry Pi 4 Bootloader

Check the bootloader version:

# check the version
vcgencmd bootloader_version
# update
sudo rpi-eeprom-update
# configuration 
/etc/default/rpi-eeprom-update
  • Adjust BOOT_ORDER configuration for the priority of different boot modes 
sudo raspi-config # 6 Advanced Options -- A6 Boot Order
# view the current EEPROM configuration
sudo rpi-eeprom-config
# edit it and apply the updates to latest EEPROM release
sudo -E rpi-eeprom-config --edit

Copy the SD card to USB/SATA device

sudo dd bs=4M if=/dev/mmcblk0 of=/dev/sda
                |           |    |      |
                |           |    `------`------ USB/SATA device
                `-----------`------------------ SD device

GPIO

General purpose input-output (GPIO) connector:

  • Uses Broadcom BCM2835 40-pin GPIO header
  • Supports 5v, 3.3v, PWM, I2C, SPI, UART (serial)
  • …pinout command show GPIO pin configuration
sudo apt install -y python3-gpiozero

# allow a user to access GPIO pins (requiers a re-login/newgrp)
sudo adduser $USER gpio

I2C/SPI

Raspberry PI SPI pinout

# install required packages
apt install -y python-smbus i2c-tools
# install kernel support
raspi-config
# select...
#       ...Interface Options, I2C or SPI Enable...

Enable a second SPI port

  • …dtoverlay=spi1-3cs in /boot/config.txt
  • …reboot required to take effect
i2cdetect -l                 # list the <i2cbus> number
i2cdetect -y <i2cbus>        # scan the I2C bus for devices    
ls -l /dev/i2c*              # check for the I2C device
ls -l /dev/spidev*           # check for the SPI device

Adafruit Blinka

Uses the Adafruit-Blinka library…

apt install -y python3 python3-pip python3-gpiozero
pip3 install adafruit-blinka

Hello world LED blinking…

  • …connect the cathode (short leg, flat side) of the LED to a ground pin
  • …connect the anode (longer leg) to a limiting resistor
  • …connect the other side of the limiting resistor to a GPIO pin (the limiting resistor can be placed either side of the LED)
#!/usr/bin/env python3

from time import sleep 
import board
import digitalio

led = digitalio.DigitalInOut(board.D25)
led.direction = digitalio.Direction.OUTPUT
 
while True:
    led.value = True
    sleep(1)
    led.value = False
    sleep(1)

Pico

Raspberry Pi Pico…

  • …built around the RP2040 microcontroller designed by Raspberry P
  • …development supported with both a C/C++ SDK, and an official MicroPython port

Hardware

References…

RP2040

Dual ARM Cortex-M0+ cores…

  • 133 MHz …264kB (on-chip) SRAM
  • AHB/APB bus fabric
  • 12 DMA channels
  • PIO state machine

Chip overview…

…green indicates connections to GPIO

Embedded ROM and SRAM…

  • …16kB read-only memory (ROM)
  • …264kB of on-chip SRAM
  • …access to external Flash via a QSPI interface
    • …using the execute-in-place (XIP) hardware
    • …software can treat flash as a large read-only memory

I/O interfaces…

  • 26 multifunction GPIO
    • …3 analog inputs
    • 2× UART
    • 2× SPI controllers
    • 2× I2C controllers
    • 16× PWM
  • 2MB on-board QSPI flash
  • USB 1.1 Host/Device controller

SIO

Single-cycle IO block (SIO)…

IOPORT …auxiliary bus port

  • …dedicated bus interface per core
  • …accessed with normal load and store instructions
  • …one cycle read/write (32-bit)
  • …SIO appears as memory-mapped hardware

RP2040 SIO

Access to…

  • CPUID …for software to determine on which core it is running
  • FIFOs (32 bits …eight entries deep) …message passing between cores
  • Hardware spinlocks …synchronisation between the cores
  • Core-local arithmetic hardware …integer divider
  • …access to peripherals that require low-latency
    • …shared GPIO register
    • …deterministic & concurrency safe access

Pinout

Mapping of pins to GPIO ports…

Raspberry Pi Pico Pinout

C/C++

Install the Raspberry Pi Pico C/C++ SDK…

# ...install dependencies on Fedora...
sudo dnf -y install \
      wget git doxygen 'arm-none-*' gcc gcc-c++ \
      automake autoconf cmake make  \
      libtool libftdi-devel libusb-compat-0.1-devel \

# clone the SDK repository ...update all sub-repositories
export PICO_SDK_PATH=~/projects/pico-sdk
git clone --branch master \
      https://github.com/raspberrypi/pico-sdk.git $PICO_SDK_PATH
(cd $PICO_SDK_PATH ; git submodule update --init)

Build a project from the Pico Examples…

# clone the source code repository from GitHub
export PICO_EXAMPLES=~/projects/pico-examples
git clone -b master https://github.com/raspberrypi/pico-examples $PICO_EXAMPLES

# ...run CMake to setup the build folder 
# ...(used to consolidating all build artifacs)
mkdir $PICO_EXAMPLES/build
(cd $PICO_EXAMPLES/build ; cmake ..)

# ..build on of the projects
(cd $PICO_EXAMPLES/build/blink ; make -j $(nproc))

MicroPython

References

Prerequisite …access to the USB devices…

sudo usermod -a -G dialout $USER
# re-login to enable this change

Install dependencies

  • …Thonny Python IDE
  • …minicom to access the serial port
# on Fedora
sudo dnf install -y thonny minicom

Firmware

Install pre-build MicroPython firmware on the device…

  • …BOOTSEL mode for programming firmware over the USB port
    • …special mode …appears as a USB Mass Storage Device
    • …hold down BOOTSEL …then connect with USB socket
    • …wait for three seconds before releasing BOOTSEL
  • …Pico appear as a removable drive …called RPI-RP2
    • …INFO_UF2.TXT …info about firmware, versions, etc.
    • …INDEX.HTM …reference to the documentation
  • …download the correct MicroPython *.uf2 file…
    • …copy the file to the device…
    • …this programs the MicroPython firmware onto the flash memory
    • …take a few seconds …board will automatically reboot
  • …default …MicroPython does not do anything when it first boots

REPL

Communicate with the MicroPython firmware over USB…

REPL (readevaluate-print loop)…

  • …use Thonny IDE
  • minicom -o -D /dev/ttyACM0
    • ctrl-d ..reboot pico
    • ctrl-a + q …exit minicom

Inspect the MicroPython firmware version…

import sys
sys.implementation

References

Hardware…

Raspberry Pi Pico…