Raspberry Pico

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PICO Pinout

Always good to put at the top.

Introduction

Install the micro ros agent

sudo snap install micro-ros-agent
sudo snap set micro-ros-agent daemon=true
sudo systemctl restart snapd

Set up Environment Variables

Here are ones I use. I believe the build system rely on PICO_SDK_PATH and PICO_TOOLCHAIN_PATH 

# Set up base directory
export PICO_ROOT=/home/$USER/dev/pico
export PICO_SDK_PATH=$PICO_ROOT/pico-sdk
export PICO_TOOLCHAIN_PATH=$PICO_ROOT/gcc-arm-none-eabi-10-2020-q4-major/bin

Get the compiler

This is how I got started.
Unzip and get the latest compiler from https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm/downloads

I then extract it to $PICO_ROOT

Clone the SDK

Get the SDK 

cd $PICO_ROOT
git clone --recurse-submodules https://github.com/raspberrypi/pico-sdk.git
git clone https://github.com/micro-ROS/micro_ros_raspberrypi_pico_sdk.git

Make the sample

It using CMake so we goto the source make a build directory and make. This should produce a file pico_micro_ros_example.uf2 

cd $PICO_ROOT
cd micro_ros_raspberrypi_pico_sdk

mkdir build
cd build
cmake ..
make

Copy to device

So plug in the PICO holding down the boot button 

cp pico_micro_ros_example.uf2 /media/$USER/RPI-RP2

Next

We can now look and see if the snap:pico slot is present with 

snap interface serial-port

This did not work the first time and the slots: section was missing. I ended up rebooting the PICO, copying the file. 

name:    serial-port
summary: allows accessing a specific serial port
plugs:
  - micro-ros-agent
slots:
  - snapd:pico (allows accessing a specific serial port)

New PICO Stuff

Spent lots of time doing lots of other stuff, ESP, learning React etc. Come back to PICO and this is note on this second view

Important

For a PICO to show up, you need to hold the BOOTSEL prior to plugging in the device. Release when powered and you should see 

Bus 003 Device 004: ID 2e8a:0003 Raspberry Pi RP2 Boot

When you copy .uf2 software to the device /media/$USER/RPI-RP2/ the device will reboot and may or may not show up depending in what the software is. E.g. 

cp ./blink.uf2 /media/$USER/RPI-RP2/

# No longer show device
# lsusb | grep 2e8a 
# Disconnects but runs the software on the PICO (i.e. it starts blinking)
sudo dmesg

[80798.165244] FAT-fs (sdf1): unable to read boot sector to mark fs as dirty

Building MicroPython From Source

Revisiting build of this using the guild. Couple of glitches, repo was incorrect but this worked for me. 

mkdir pico
cd pico
git clone  https://github.com/micropython/micropython
cd micropython/
cd lib/pico-sdk
git submodule update --init
sudo apt install cmake gcc-arm-none-eabi build-essential
cd ../..
make -C mpy-cross
cd ports/rp2
make

Building picotool From Source

sudo apt install build-essential pkg-config libusb-1.0-0-dev
export PICO_SDK_PATH=/home/iwiseman/dev/projects/pico/pico/micropython/lib/pico-sdk

git clone https://github.com/raspberrypi/picotool
cd picotool
mkdir build
cd build
cmake ..
make
# optional
sudo cp /home/$USER/dev/projects/pico/pico/picotool/build/picotool /usr/bin/picotool

Using Ros 2 and Pico


This is important because I could not get the Pico to create a /dev/ttyACM0

Pico-Exampleas

Building

This took some time because I tried to build the examples individually. 

# Clone and build
git clone https://github.com/raspberrypi/pico-examples
cd pico-examples
makedir build
cd build
cmake ..
make

Doing this with just an one example e.g. 

cd hello_world/
mkdir build
cd build/
cmake ..

Results in the following error 

CMake Warning (dev) in CMakeLists.txt:
  No project() command is present.  The top-level CMakeLists.txt file must
  contain a literal, direct call to the project() command.  Add a line of
  code such as

    project(ProjectName)

  near the top of the file, but after cmake_minimum_required().

  CMake is pretending there is a "project(Project)" command on the first
  line.
This warning is for project developers.  Use -Wno-dev to suppress it.

CMake Error at serial/CMakeLists.txt:9 (pico_add_extra_outputs):
  Unknown CMake command "pico_add_extra_outputs".

Serial vs USB

They look the same but they are not. Here is the difference in the USB makefiles 

    # enable usb output, disable uart output
    pico_enable_stdio_usb(hello_usb 1)
    pico_enable_stdio_uart(hello_usb 0)

C++ Example

Create demo program 

#include <stdio.h>
#include <pico/stdlib.h>

int main()
{
    stdio_init_all();

    while (true) {
        printf("Hello world\n");
        sleep_ms(1000);
    }
}

And a CMakefile 

cmake_minimum_required(VERSION 3.13)

include($ENV{PICO_SDK_PATH}/external/pico_sdk_import.cmake)

project(myapp C CXX ASM)

set(CMAKE_C_STANDARD 11)
set(CMAKE_CXX_STANDARD 17)

pico_sdk_init()

add_executable(${PROJECT_NAME} main.c)

pico_add_extra_outputs(${PROJECT_NAME})

target_link_libraries(${PROJECT_NAME} pico_stdlib)

pico_enable_stdio_usb(${PROJECT_NAME} 1)
pico_enable_stdio_uart(${PROJECT_NAME} 0)

Create a build directory and build 

mkdir build 
cd build
cmake ..
make -j$(nproc)

Copying the software to the Pico and monitoring with screen gives 

cp myapp.uf2  /media/iwiseman/RPI-RP2/

sudo screen /dev/ttyACM0 115200

Hello world
Hello world
Hello world
....
# CTRL+A \ to exit

PIO and the PICO

Sounds like a new book but this is reminding myself of the old C64 and assembly. Starting with the blink project and reading until tired.

Blink

Prerequisites

We need to have a working PICO sdk mine is in 

PICO_SDK_PATH=/opt/pico/pico-sdk

CMake file

For CMake I have cmake 3.22.1 

# Set minimum required version of CMake
cmake_minimum_required(VERSION 3.12)

# Include build functions from Pico SDK
include($ENV{PICO_SDK_PATH}/external/pico_sdk_import.cmake)
include($ENV{PICO_SDK_PATH}/tools/CMakeLists.txt)

# Set name of project (as PROJECT_NAME) and C/C   standards
project(blink C CXX ASM)
set(CMAKE_C_STANDARD 11)
set(CMAKE_CXX_STANDARD 17)

# Creates a pico-sdk subdirectory in our project for the libraries
pico_sdk_init()

# Tell CMake where to find the executable source file
add_executable(${PROJECT_NAME} 
    src/main.c
)

# Create C header file with the name <pio program>.pio.h
pico_generate_pio_header(${PROJECT_NAME}  
        ${CMAKE_CURRENT_LIST_DIR}/src/blink.pio
)

# Create map/bin/hex/uf2 files
pico_add_extra_outputs(${PROJECT_NAME})

# Link to pico_stdlib (gpio, time, etc. functions)
target_link_libraries(${PROJECT_NAME} 
    pico_stdlib
    hardware_pio
)

# Enable usb output, disable uart output
pico_enable_stdio_usb(${PROJECT_NAME} 0)
pico_enable_stdio_uart(${PROJECT_NAME} 1)

C Code

Nothing special here 

#include <stdio.h>
#include <stdbool.h>
#include <pico/stdlib.h>
#include <hardware/pio.h>
#include <blink.pio.h>

#define LED_BUILTIN 25

int main() {
  stdio_init_all();

  PIO pio = pio0;
  uint state_machine_id = 0;
  uint offset = pio_add_program(pio, &blink_program);

   blink_program_init(pio, state_machine_id, offset, LED_BUILTIN);

  while(1) {
    //do nothing
  }
}

PIO Code

This is the C64 bit you make a file call blink.pio which contains assembly and C-SDK bindings which seem like a bit of voodoo and hope to learn more. The assembly is straight forward. 

.program blink

set pindirs, 1      ; Set pin to output
loop:
  set pins, 1 [31]  ; Drive pin high and then delay for 31 cycles
  set pins, 0 [31]  ; Drive pin low and then delay for 31 cycles
  jmp loop
  
% c-sdk {

static inline void blink_program_init(PIO pio, uint sm, uint offset, uint pin) {

  // 1. Define a config object
  pio_sm_config config = blink_program_get_default_config(offset);

  // 2. Set and initialize the output pins
  sm_config_set_set_pins(&config, pin, 1);

  // 3. Apply the configuration & activate the State Machine
  pio_sm_init(pio, sm, offset, &config);
  pio_sm_set_enabled(pio, sm, true);
}

%}

Breakdown of PIO Instructions

The SDK provides

500
500
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