Kria KR260 + Rpi SenseHAT-LEDMatrix on Petalinux [Part II]

This tutorial is focused on "How to interface SenseHAT LED Matrix Display with KR260 in Petalinux".

This tutorial is "Part II" tutorial on Raspberry Pi Sense Hat Integration on Petalinux with Kria KR260.

For details of VIVADO block design and Petalinux flow for "how senseHAT based design be created on VIVADO for Kria KR260", please follow "Part I- SenseHAT sensors interfacing with Kria KR260 in Petalinux" tutorial.

Tools Version used: VIVADO/Vitis and Petalinux - 2022.2

Detail version of this "Tutorial" is also available in PDF format at footer section of this tutorial (Download it).

Design Files of this Project:

We have provided VIVADO Tcl, XDC file, Petalinux BSP file (ready to build BSP file), drivers and python application for SenseHAT sensors and LED Matrix at: https://github.com/LogicTronix/KR260-SenseHAT-Petalinux [Git Branch: KR260-SenseHAT-LedMatrix].

You can clone git repo of this tutorial by:

git clone -b KR260-SenseHAT-LedMatrix https://github.com/logictronix/kr260-sensehat-petalinux

Working of the Sense HAT LED Matrix

The LED Matrix on the Sense Hat is driven by the led2472g IC which is a LED driver manufactured by STMicroelectronics. This LED driver is controlled by ATTiny88. The ATTiny88 acts as a slave on the IIC bus and can be accessed at 0x46 slave address.

The Sense HAT python API uses 8 bit (0 to 255) colors for R, G and B components of a pixel. When these values are written to the Linux frame buffer they're bit shifted into RGB 5 6 5. The driver converts them to RGB 5 5 5 before it passes them to the ATTiny88 AVR for writing to the LEDs.

VIVADO Block Design

The VIVADO Block design can also be created from the given Tcl Source[Link],

Sense HAT - KR260 Header Alignment

The Sense HAT sits over the RPi header on the KR260 as shown in the picture above. The description of the 40 pins is shown for this alignment. The sensors communicate over I2C which uses pins 3 and 5.

Constrainting

Only 2 pins (AE14 and AE15) on the KR260 require constraining for I2C to work. AE15 is used for SDA and AE14 is used for SCL.

set_property PACKAGE_PIN AE15 [get_ports {iic_sda_io}]
set_property IOSTANDARD LVCMOS33 [get_ports {iic_sda_io}]
set_property PULLUP true [get_ports {iic_sda_io}]

set_property PACKAGE_PIN AE14 [get_ports {iic_scl_io}]
set_property IOSTANDARD LVCMOS33 [get_ports {iic_scl_io}]
set_property PULLUP true [get_ports {iic_scl_io}]

However, the following image can be used as a reference to map and constrain all other pins.

Generating XSA

• From the File menu, select Export > Export Platform.
• Select the Hardware option in the Platform Type window.

• Select the Pre-Synthesis state and also select the Include bitstream option in the Platform State window.

• Change required Platform Properties.

• Enter a name for the XSA and select a folder to export the XSA to and select Finish.

Petalinux Flow

Sense HAT Sensor's Driver Availability

C/C++ Drivers for most sensors are available from the vendor themselves. Some drivers are also written by independent developers.

Humidity/Temperature

• https://github.com/STMicroelectronics/hts221-pid

Accelerometer/Gyroscope and Magnetometer

• https://github.com/STMicroelectronics/lsm9ds1-pid

Pressure/Temperature

• https://github.com/ameltech/sme-lps25h-library
• https://github.com/kirananto/RaZorReborn/tree/master/drivers/sensors/pressure/lps25h

LED Driver

• https://github.com/raspberrypi/linux/pull/1043/files
• https://github.com/jbroutier/LED2472G-driver

Petalinux Project- Prerequisites

Creating a petalinux project requires a supported BSP which can be downloaded from the link below. A project also can be created without the BSP which is less convenient.

• Download the KR260-SenseHAT BSP from: https://github.com/LogicTronix/KR260-SenseHAT-Petalinux/tree/KR260-SenseHAT-LedMatrix/design_files
• This provided BSP already has configured the necessary packages and drivers, so it can be directly build. Or you can update the "Hardware on this BSP" using Get-Hardware-Config command of Petalinux.

Create Petalinux Project with provided BSP and Build it:

petalinux-create --type project -s <location-to-bsp> --name <project-name>
cd  <project-name>
petalinux-build

• On this provided BSP, we have included "KR260 App in the RootFS", so the Kria App automatically loads while booting on the KR260-Board.
• We also have added SenseHAT drivers by creating "recipes-modules" on this BSP file itself. Further details of the "SenseHAT" drivers can be found at: https://github.com/LogicTronix/KR260-SenseHAT-Petalinux/tree/KR260-SenseHAT-LedMatrix/driver
• So "petalinux-build" basically did all config and build the petalinux project.

Generating/Creating a Bootable Image

Run the following command to create a bootable WIC image.

petalinux-package --wic --images-dir images/linux/ --bootfiles "ramdisk.cpio.gz.u-boot, boot.scr, Image, system.dtb, system-zynqmp-sck-kr-g-revB.dtb" --disk-name "sda"

• Make sure the dtb file is present in the <petalinux-project-dir>/images/linux/ directory.

• Burn the SD card with the WIC image, and boot up the KR260 board (with SenseHAT).
• On this WIC image, the "kr260 overlay" is automatically added on "RootFS of WIC image", the BSP have that configuration. So this step sort-out(remove) steps like "copying dtbo, bit.bin and shell.json" into Board(/lib/firmware/xilinx/) manually.

Loading the Overlay and Detecting Devices on the I2C Bus

List the apps present on the device.

sudo xmutil listapps

Unload the current app.

sudo xmutil unloadapp

Load your app (kr260 in this case).

sudo xmutil loadapp kr260

Check if the XIIC is listed as an I2C bus in the system.

i2cdetect -l

• This will list all the I2C bus in the system (i2c-7 in this case).
• If the bus is unavailable, unload and load the app again.

Check for devices on the XIIC bus.

• sudo i2cdetect -y -r <i2c-bus-number>
• This will show the address of the sensors connected to the I2C bus.
• If the Sense Hat is working, it should show the following addresses.
• The following address map of I2C bus 7 shows all the sensor addresses from the Sense HAT. These addresses are also listed in table 1.

• Make the bus accessible to your user group by running the following command.
• sudo chown root:petalinux /dev/i2c-<bus_number> && sudo chmod g+rw /dev/i2c-<bus_number>
• e.g. sudo chown root:petalinux /dev/i2c-7 && sudo chmod g+rwx /dev/i2c-7

Communicating with the Sensors with Python

To communicate with the sensors attached to the bus with python, a python package needs to be installed.

Installing SMBus

To install SMBus, run pip3 install smbus. SMBus provides python bindings for Linux SMBus access through i2c-dev.

KR260-SenseHAT-Petalinux repo

Git Repo Structure:KR260-SenseHAT-Petalinux [Git Branch: KR260-SenseHAT-LedMatrix]

[Optional] Running Git-Repo on KR260 Board(Direct Method)

Writing Python Script

To communicate with the sensors, we require an object of the SenseHat class that provides us with various functions that make communicating easier. We create a new instance of the SenseHat class by passing the I2C bus number that our sensors are attached to.

sense = SenseHat(<i2c-bus-number>)

With the sense object, we can access the following functions that help us read data from the sensors.

For a list of available functions and properties, check out the readme at https://github.com/LogicTronix/KR260-SenseHAT-Petalinux/tree/KR260-SenseHAT-LedMatrix.

Code Snippet for Reading Temperature

from time import sleep
from sense_hat import SenseHat
# 7 is I2C bus
sense = SenseHat(7)
while True:
# Temperature
print(f'\nTemperature\t: {sense.temp:.4f}° C')
print(f'\nTemperature\t: {sense.temperature:.4f}° C')
print(f'\nTemperature\t: {sense.get_temperature_from_humidity():.4f}° C')
print(f'\nTemperature\t: {sense.get_temperature_from_pressure():.4f}° C')
print(f'\nTemperature\t: {sense.get_temperature():.4f}° C')
# Humidity
print(f'Relative Humidity\t: {sense.humidity:.4f} %')
print(f'Relative Humidity\t: {sense.get_humidity():.4f} %')
# Pressure
print(f'Pressure\t: {sensor.pressure():.4f} hPa')
print(f'Pressure\t: {sensor.get_pressure():.4f} hPa')
sleep(1)

Output from the Sensors

Temperature and Humidity reading from the HTS221 sensor

Temperature and Pressure reading from the LPS25H sensor

Acceleration, Magnetometer and Gyroscope reading from the LSM9DS1 sensor

Code Snippet for LED Matrix

Displaying Information on the LED Matrix

from time import sleep
from sense_hat import SenseHat
# 7 is I2C bus
sense = SenseHat(7)
while True:
sense.show_message('Hello World.')
sense.show_message(f'{sense.get_temperature_from_humidity():.4f}° C')
sleep(1)

Displaying 8x8 RPi Logo on the LED Matrix

from sense_hat import SenseHat
# 7 is I2C bus
sense = SenseHat(7)
while True:
sense.load_image('rpi.png', redraw=True)

Demo - Pictorial:

Video Demo: KR260+ SenseHAT:

Again, for VIVADO, Petalinux project source and Python source code, check: Github or run following Git clone command at your terminal:

git clone -b KR260-SenseHAT-LedMatrix https://github.com/logictronix/kr260-sensehat-petalinux

Thanks to Frank Shrestha [frank_shrestha@logictronix.com] for creating this "in-depth" tutorial!