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Speaking CAN: Request and Response

Controller Area Networks (CANs, for short) are used for the communication between electronic control units (ECUs) in cars, trucks, tractors, harvesters, construction machines, packaging lines and e-bikes. Qt provides the Qt CAN Bus API as part of its QtSerialBus module. Qt CAN Bus provides a clean and simple API to connect to a CAN bus, to send and receive CAN frames over the CAN bus.

When we build an HMI application to control a machine, we need a lot more functionality than the Qt CAN Bus API should offer. The HMI application must not send CAN frames too fast to avoid buffer overflows in the CAN controller. When the HMI application receives, say, more than 200 CAN frames per second and tries to display the changes, it will freeze. The HMI application must be able to recover from CAN bus errors. We do not want to write the code for serialising and deserialising thousands of CAN messages manually, but want to generate this code automatically.

I’ll show solutions to these problems in a loose series of blog posts called Speaking CAN. In this first post, I’ll explain how an HMI application running on a display computer retrieves the value of a parameter from an ECU. The terminal sends a request to the ECU over CAN and receives a response from the ECU over CAN.

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Using Qt under LGPLv3

At Qt Day 2019 in Florence, Italy, I gave a talk Using Qt under LGPLv3. In the first part The obligations of Qt LGPLv3: made understandable, I explain in detail, how you must provide the source code, the license texts, the copyright notices, any modification notices and the installation information. You don’t have to provide the installation information for B2B products like driver terminals in commercial vehicles, industrial devices and medical devices in hospitals. In other words, you don’t have to satisfy the anti-tivoisation rule for B2B products.

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Using Docker Containers for Yocto Builds

We want to build a custom Linux image with Yocto for the Raspberry Pi 3 model B (BCM2837). The Linux image contains a very simple Internet radio application using Qt 5.11 and the eglfs graphics backend. Our colleagues shall be able to repeat the build easily – now, in three years and even in ten years.

I’ll explain why Docker is an excellent choice to build custom Linux images and give you a step-by-step guide how to do it. At the end of the post, you will be able to run a simple Internet radio on a custom Linux image on a Raspberry Pi 3.

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Book Review: “It Doesn’t Have to Be Crazy at Work” by Jason Fried and David Heinemeier Hansson

My favourite business book of 2018 is It Doesn’t Have to Be Crazy at Work by Jason Fried and David Heinemeier Hansson. The reason why people work crazy hours is not that there is

[…] more work to be done all of a sudden. The problem is that there’s hardly any uninterrupted, dedicated time to do it. People are working more but getting less done. It doesn’t add up – until you account for the majority of time being wasted on things that don’t matter.

The authors call out working crazy hours for not being “a badge of honor” but “a mark of stupidity”. Yes, it’s good to hear this from people who know what they are talking about. Jason is the CEO and David the CTO of Basecamp, which they have been running very successfully since 2003. They describe in the book how – at Basecamp – they replaced crazy at work with calm at work.

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High-Speed-Data (HSD) Connectors in Heavy-Duty Vehicles

In a recent blog post, I suggested to replace multiple display computers in a driver cabin by one computer in a silver box with multiple displays. I didn’t specify which connectors and cables to use between computer and displays. I found the answer at Electronica 2018 last week: High-Speed-Data or HSD connectors. You can use HSD connectors for LVDS (including Display Port), APIX, CAN, USB 2.0, USB 3.0, Ethernet and Firewire.
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Tremendous Speed-Up with SQL Transactions

The function CustomerDatabase::importCustomers reads 500 customers from the list c_customers, creates an SQL query cmd for each customer and inserts each customer into the Customers table of the SQL database db.

void CustomerDatabase::importCustomers() {
    auto db = QSqlDatabase::database("CustomerDB");
    for (auto row : c_customers) {
        auto cmd = QString{"INSERT INTO Customers "
                   "(fullName, street, postalCode, city, phone, email) "
                   "VALUES (\'%1\')"}.arg(row.join("\', \'"));
        auto query = QSqlQuery{cmd, db};
    }
}

On an NXP i.MX6 SoC with four Cortex-A9 cores, this function takes 17.5 seconds! Your user would have to wait more than 17.5 seconds for the import of a CSV file with 500 customers to finish. This is unacceptable. How can you speed up the import to 0.2 seconds?
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