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Zephyr board bring-up walkthrough

Commands and notes for the 25/04/2024 Zephyr Tech Talk.

Setup folder

  • Start from a clean sample directory

Do all the setup steps in Readme, then clone a new example-application with west init:

west init -m https://github.com/zephyrproject-rtos/example-application --mr main my-workspace

Don’t git clone directly, it creates a weird path.

  • Update Zephyr modules
cd my-workspace
west update
  • Try compilation
cd example-application
BOARD="custom_plank"
west build -b $BOARD -p always app

Create our board

  • Find a similar board dts to copy Copy a board, to have presets and example configs

  • SoC: STM32F405, but we can take an exemple from the same SoC series, and change SoC, for the demo

cd $Z/boards
grep -rnw ./ -e "name: stm32f40.*"
  • Choosing stm32f4_disco as a ref design - not the right SoC but we’ll change it
cp -r $Z/boards/st/stm32f4_disco/ ./boards/st

Rename board files

rename "s/stm32f4_disco/totoboard/g" ./*
grep -rnw ./ -i -e ".*stm32f4_disco"
sed -i 's/stm32f4_disco/totoboard/' totoboard.yaml
sed -i 's/stm32f4_disco/totoboard/' board.yml
sed -i 's/STM32F4_DISCO/TOTOBOARD/' Kconfig.totoboard

  • Docs folder can be updated later, it is mandatory if you want to contribute your board to Zephyr main

  • Not mandatory but nice: customize compatible = "st,totoboard" and model description in dts file

Try the board

BOARD="totoboard"
west build -p always -b $BOARD app
  • It looks for examplesensor0, which is not here in our dts

Import blinky

cp -r $Z/samples/basic/blinky ./
west build -p always -b $BOARD blinky

Don’t flash this, it still needs customizations.

  • "zephyr,led0" in dts allows to choose the led actually blinked by software
  • You can see the call to zephyr,led0 if you open the blinky.c source
vim $Z/samples/basic/blinky/src/main.c

DTS customisation

  • Now modify the DTS file to match the board.

SoC selection

find ./ -name "stm32f407Xg.dtsi"

The SoC description file is:

$Z/dts/arm/st/f4/stm32f4/stm32f405Xg.dtsi

The pinctrl file is:

find ../ -name "stm32f407v(e-g)tx-pinctrl.dtsi"
./modules/hal/stm32/dts/st/f4/stm32f407v(e-g)tx-pinctrl.dtsi

  • Pincontrol file: check your board chip name (me: stm32f405vgtx-pinctrl because I have STM32F405VGT6)

  • X is a standard wildcard for component name

  • Also, change the SoC in board.yaml

grep -rnw ./ -e ".*stm32f407.*"

Open schematics and find a LED + UART

Open schematics for the board.

  • Orange LED: PC13 Active HIGH

  • Blue button: PC14 Active LOW

  • Rapid pull-up / pull-down check on schematics

  • Usart accessible on USB port through ST-Link: Usart 6

  • PC6/USART6_TX

  • PC7/USART6_RX

  • Remove can busses, disable OTG

  • Change zephyr,shell to usart6

Clock frequency

Check the main clock

  • OSC_IN -> NX3225GD-8MHZ
  • HSE is 8 MHz in DTS
  • There is a nice macro to avoid writing lots of zeros in frequency fields (in $Z/dts/common)

Build and flash and run

west build -p always -b $BOARD blinky
west flash

Results: LED should blink and UART messages should be displayed.

Shells

Enable GPIO shell

tree -L 2 blinky

prj.conf: selects what will be build

In blinky prj.conf, add:

CONFIG_SHELL=y
CONFIG_GPIO_SHELL=y

Now, are you unsure about the option name? Should it be gpio shell or shell gpio? Open the option catalogue, menuconfig:

west build -t menuconfig
  • Log level for LED Either put the logs on UART2 (zephyr,console=&usart2), or disable logs by modifying blinky sample.

Use shell GPIO

gpio help
gpio info
  • Yellow LED is on PC4
gpio conf

Gpio referenced by addresses, not nice names! So, tips to find the register address for our GPIOC peripheral:

  • Pre-built DTS
vim ./build/zephyr/zephyr.dts
gpioc: gpio@40020800
  • DTS visualition tool
dtsh
tree --format NKYC
  • Setup GPIOC 4 to active high output and set to 1
gpio conf gpio@40020800 4 oh0
gpio set gpio@40020800 4 1

gpio blink gpio@40020800 4 1

  • GPIO blink: useful for measurements with oscillo trigger?

  • Read GPIO User button PC14

gpio conf gpio@40020800 14 i
gpio get gpio@40020800 14

1 if not pressed, 0 if pressed

gpio conf gpio@40020800 14 il

0 if not pressed: OK

Devmem shell

Read and modify misc peripheral config with devmem.

CONFIG_DEVMEM_SHELL (enabled by default)

Easy sample with input vs output

Register offset page 284

GPIO 0 controlled by the 2 lower bits

gpio conf gpio@40020800 0 i
devmem 40020800 32
gpio conf gpio@40020800 0 o
devmem 40020800 32

-> See 00 (Input state) become 01 (Output mode)!

Can also write in devmem:

devmem 40020800 32 0x400a000

I2C shell

  • Output connector I2C:
PB10/I2C2_SCL
PB11/I2C2_SDA
  • From boards/st/nucleo_f411re/nucleo_f411re.dts:
&i2c1 {
        pinctrl-0 = <&i2c1_scl_pb8 &i2c1_sda_pb9>;
        pinctrl-names = "default";
        status = "okay";
        clock-frequency = <I2C_BITRATE_FAST>;
};

Copy and modify

CONFIG_I2C=y
CONFIG_I2C_SHELL=y

Build

  • Time to mention SPI shell exists and was just merged

  • Similar to i2cset/get and spidev in Linux, don’t need my Pi anymore

  • First, show scan without daughter board: nothing displayed.

I2C shell but this time it works

Then, with daughter board plugged in:

  • Scan
i2c scan i2c@40005800
2d 53 57

Page 64 / page 159: I2C adresses are 0x53 and 0x57 (7-bits)

  • Read I2C
i2c read i2c@40005800 53 0
  • PE7 device enable / disable It’s called ST25DX SPARE, and can be selected onboard, but also controlled by SoC
gpio get gpio@40021000 7

gpio conf gpio@40021000 7 o
gpio set gpio@40021000 7 1

-> Disables I2C device

  • Can be used for osc measurements

  • End of part 3: shell!

Bringup complex subsystem

Systems that cannot just be checked with GPIO / i2c / spi simple commands.

Display

Let’s say I made an advanced DTS Switching back to:

BOARD="st25dv_mb1283_disco"

Simple sample:

cp -r ~/zephyrproject/zephyr/samples/drivers/display/ ./
west build -p always -b $BOARD display

Open the dts in:

vim $Z/boards/st/st25dv_mb1283_disco/st25dv_mb1283_disco.dts

For display, I added:

  • SPI2 activation
  • display driver using this SPI bus
  • zephyr,display chosen to tell Zephyr where is the display
  • header for some variables

USB

cp -r ~/zephyrproject/zephyr/samples/subsys/usb/testusb/ ./
west build -p always -b $BOARD testusb

  • Open dts to check how usb is described

  • lsusb: NordicSemiconductor Zephyr testusb sample

FAQ preshots

SPI shell

Just merged! It will look like this:

uart:~$ spi transceive spi@40013000 49 0

Clock tree config

Currently manufacturer dependant. In case of ST, use STMCube configurator, or SoC clock tree schem page 154, and some magic.

vim $Z/dts/bindings/clock/st,stm32f4-pll-clock.yaml

See RFC & talk by Daniel DeGrasse

More explanations about device tree

I did a lot of arbitrary copy-pasting, explanation:

DTS bindings

  • Describe DTS options, also count as code, sort of codumentation

For UART:

vim $Z/dts/bindings/serial/uart-controller.yaml
vim $Z/dts/bindings/serial/st,stm32-uart-base.yaml

Where are pinmuxes defined?

In the pinctrl file we chose earlier.

~/zephyrproject/modules/hal/stm32/dts/st/f4/stm32f405zgtx-pinctrl.dtsi
  • manufacturer specific macro stuff, grep "define STM32_PINMUX" and "define PIN_NO" if questions.

Why devmem?

Devmem: read and write register values by hand instead of using software abstraction! But why?

  • What if you need an option that is not in the shell GPIO i/o/h/l toggles
  • Try some pull-up strength, speed settings, for signal integrity or EMC For instance, slew-rate, in bindings
/dts/bindings/pinctrl/st,stm32-pinctrl.yaml

GPIOx_OSPEEDR
GPIOC: 40020800
  • Register map page 285: Address offset: 0x08 for OSPEEDR
  • 0 by default
  • 0x2000 0000 for high speed offset 14