Written by David Leach, Software Architect at NXP Semiconductor and member of the Zephyr Technical Steering Committee

Last month, the Zephyr Project announced the release of Zephyr RTOS 2.1. A long list of enhancements and bug fixes contained in Zephyr 2.1 can be found in the release notes. 

Major Enhancements

·         Normalized APIs across all architectures.

·         Expanded support for ARMv6-M architecture.

·         Added support for numerous new boards and shields.

·         Added numerous new drivers and sensors.

·         Added new TCP stack implementation (experimental).

·         Added BLE support on Vega platform (experimental).

·         Memory size improvements to Bluetooth host stack.

The Numbers

This release is the result of the hard work and skill of over 350 individuals engaged with the project over the last 3 months with over 1500 PRs merged and 532 issues closed. We would like to thank all those who engaged with the project both in front and behind the scenes to help improve the Zephyr Project for this release.

Sample boards that now have support

What’s Next

Improvements to Zephyr Project never stops. Work continues on the new TCP stack implementation, many different activities with Bluetooth, converting GPIO drivers to the new GPIO API,  and many other enhancements and bug fixes.

Join Us

We invite you to try out Zephyr 2.1. You can find our Getting started Guide here.  If you are interested in contributing to the Zephyr Project please see our Contributor Guide. Join the conversation or ask questions on our Slack channel or Mailing List.

By Maureen Helm, Chair of the Zephyr Project Technical Steering Committee

The Zephyr community converges every year at the Embedded Linux Conference Europe, and 2019 was no exception. This year we traveled to Lyon, France for an engaging week full of technical talks, spontaneous hallway conversations and hacking sessions, team dinners, and perhaps a nice glass of wine or two. It was a wonderful opportunity to get to know some of our newer members in person and finally put faces to familiar names and voices.

After the main conference, the Zephyr technical steering committee stayed on for two days of face-to-face meetings, including a few dial-ins from those who couldn’t make the trip. Compared to our weekly calls, the longer format F2F meeting allowed us to discuss and debate issues in greater depth, and make decisions about the technical direction of the project.

#1 – Mainline releases: Historically we have aimed for quarterly releases, but will shift to a 4-month cycle in 2020. More details, including dates, are in the Program Management wiki page.

#2 – LTS releases: We clarified that LTS releases will be maintained for two years, and LTS2 will be released approximately two years after LTS1. We did not decide on a cadence beyond LTS2.

#3 – Toolchains: We agreed that multiple members have an interest in supporting commercial toolchains and will kickoff a new toolchain-focused working group.

#4 – User Experience: We brainstormed possible solutions to common problems encountered by new developers.

#5 – Roles and Responsibilities: We debated a contributor ladder towards maintainership, how to distribute merge rights, and how to fill the release manager role for future releases. This conversation has continued in subsequent process working group meetings.

Thank you to everyone who joined, and I look forward to seeing you next time at the Embedded Linux Conference in Austin, Texas!

This blog originally ran on the Antmicro website. For more Zephyr development tips and articles, please visit their blog.

Solving problems that require real-time calculations and precise control typically calls for using an RTOS. While we have been working with a wide variety of RTOSs for various applications (like Contiki-NG for IoT, RTEMS for space applications, eCos for satellite equipment, FreeRTOS in many other fields etc), Antmicro’s RTOS of choice these days has been Zephyr, a Linux-Foundation driven, well-structured, vendor-independent and scalable real-time OS. We’ve ported and adapted Zephyr to many platforms, encouraged its use as a standard on RISC-V, promoted it in less standard contexts like FPGA devices.

So if you have a single device with a real-time requirement, typically it’s not that hard to decide how to approach the problem – just use Zephyr!

The problem starts when there are multiple heterogeneous devices that have to communicate in a standardised and robust way, performing a complex operation involving a network protocol while never leaving the “real-time” world. Scenarios like this are typical in the aerospace, automotive, robotics industries, and increasingly those industries are looking to reuse technologies known from the commercial/consumer market to leverage the massive scale offered by omnipresent, commodity tech.

For your everyday use case, the easiest way to connect multiple devices is of course Ethernet, but plain old Ethernet does not list real-time capabilities in its dictionary – how then can it be used in a real-time use case?

The set of standards that define Time Sensitive Networking is the answer to that problem. Leveraging the physical and logical foundations of Ethernet and extends it to cover real-time use cases by defining different aspects of time sensitive communication: clock synchronization, traffic shaping, scheduling, fault tolerance etc.

TSN seems then like a good fit, and sure enough, open source support for TSN is widely available in Linux. In the RTOS world however, there has previously not existed a proper implementation of TSN, readily available and tested on real hardware platforms, well, not until Zephyr 1.13!

Initial work: towards a TSN implementation in Zephyr

As a member of the Zephyr Project, Antmicro is always excited to add new functionalities to the OS, especially in fields that open it up for adoption in new use cases. Here, we were happy to work with another Zephyr project member, Intel on getting gPTP support added to Zephyr. “gPTP” stands for “generic Precision Time Protocol” and is responsible for clock synchronization. When we joined the project it was already in progress, but far from being finished. We implemented the missing state machines and fixed various bugs in the existing code.

The initial target was making Zephyr’s clocks synchronize with external Grand Masters.

Our focus was getting it to work on Microchip SAM E70 Xplained. At that time, the platform already had a Zephyr port (including the Ethernet driver), but it lacked drivers for the PTP clock.

The TSN support was also tested on the NXP FRDM K64F development platform which also has a Zephyr port and hardware timestamping support.

After initial support was done and merged, we proceeded with configuring Zephyr nodes as Grand Masters, as well as ensuring operational Zephyr-to-Zephyr clock synchronization.

Qav: an important part of TSN

PTP is only a part of Time Sensitive Networking. Another important part of TSN is queue management.

The platform of our choice (SAM E70 Xplained) has multiple hardware queues built into its MAC controller, which allowed us to use the same platform to extend Zephyr’s TSN capabilities.

Antmicro implemented support for credit-based shaper algorithms in Zephyr, which are described in the 802.1Qav standard.

The work in that area required us to design an API to manage the Qav-capable Ethernet queues. Through this API/management interface, we made it possible to set and read various parameters, like idle slope, delta bandwidth, traffic class, etc.

Additionally, some status parameters were implemented. These are now shown in the regular networking shell in Zephyr for the supported network interfaces.

Running a basic Zephyr gPTP sample application

To find out how to run the basic gPTP sample, please refer to Zephyr’s official documentation.

More general info about the gPTP stack implementation can be found in a dedicated chapter.

Testing in Renode Cloud Environment

A network stack plays a critical role in an operating system like Zephyr. It is also constantly under very heavy development by various parties. Our work on the TSN/gPTP support was heavily influenced by all the changes in the networking subsystem. As can be expected in large development campaigns, these completely unrelated things would break our implementation repeatedly.

The reason for that was lack of more sophisticated testing of the setup. Sure, there were multiple unit tests which directly tested our stack implementation, but Time Sensitive Networking can be broken by seemingly minor changes in other parts of the networking stack.

Obviously, network protocol testing is difficult. You can either use synthetic tests that easily get outdated and don’t really reflect real life scenarios or you can create complicated physical network setups connected to a CI system – which is costly, difficult to maintain and creates only a single, static configuration.

A much better, more scalable solution is to use simulation. With Antmicro’s Renode open source simulation framework you can create script-defined complex configurations, allowing you to verify virtually every scenario imaginable.

In Renode’s 1.7 release, Antmicro added support for the SAM E70 platform, along with Ethernet with gPTP capabilities. With these new features we were able to create a CI setup testing upstream Zephyr in a virtual environment.

And thanks to an integration with the Robot Framework, it’s very easy to create new test cases in Renode. That’s why, for Zephyr, we decided to create a suite of tests verifying a range of aspects of a single application.

This lines up perfectly with the introduction of Renode Cloud Environment – a new CI system introduced by Antmicro, that you’ll be able to read about more on our blog soon. Here is a sneak peek of the TSN testing setup running in RCE.

First, Renode verifies if the board sends a PTP packet, which means that the PTP stack is started properly. Next, we analyze its reception and the proper reaction from the recipient’s OS. We analyze whether the compile-time configuration of the PTP stack is properly reflected in its runtime, and the highest level properties: whether the correct Grand Master node has been selected and whether the slave nodes are properly synchronizing their clocks.

The whole testing setup can be easily recreated with upstream Renode and Zephyr. For instructions, please refer to the TSN testing tutorial.

Building a TSN system?

If you’d like to use TSN is your system, and feel that an RTOS like Zephyr is a good fit for your needs, be sure to reach out to us at contact@antmicro.com – we’d be happy to help you apply TSN on existing and new hardware, and perhaps in simulation, for real-world use cases!

This blog originally ran on the Antmicro website. For more Zephyr development tips and articles, please visit their blog.

Antmicro’s open source simulation framework, Renode, was built to enable simulating real-life scenarios – which have a tendency to be complex and require hybrid approaches.

That’s why, besides other things, the Renode 1.7.1 release has introduced an integration layer for Verilator, a well known, fast and open source HDL simulator, which lets you use hardware implementations written in Verilog within a Renode simulation.

When you are working on ASIC or FPGA IP written in an HDL, forming a part of a bigger system with unknowns both in the hardware and software, many things can go wrong on multiple levels. That’s why ultimately it’s best to test it within the scope of the full system, with drivers and test software, in a real-world use case. Simulating complete platforms with CPUs and all peripherals using actual HDL simulation, however, can be too slow for effective software development (and sometimes downright impossible, e.g. when access to the entire SoC’s HDL is not available). Renode models will give you better speed and flexibility to experiment with your architectural choices (as in the security IP development example of our partner Dover Microsystems) than HDL, but there might still be scenarios where you could quickly try to directly use complex peripherals you already have in HDL form before going on to model them in Renode. For these use cases Antmicro has enabled the option of co-simulating HDL in Renode using Verilator. Co-simulating means you’re only ‘verilating’ one part of the system, and may in turn expect a much faster development experience than with trying to perform an HDL simulation of the whole system.

In the 1.7.1 release of Renode you will find a demo which includes a ‘verilated’ UARTLite model connected to a RISC-V platform via the AXI4-Lite bus running Zephyr.

Integration layer overview

The integration layer was implemented as a plugin for Renode and consists of two parts: C# classes which manage the Verilator simulation process, and an integration library written in C++ that allows you to turn your Verilog hardware models into a Renode ‘verilated’ peripheral.

The ‘verilated’ peripheral is compiled separately and the resulting binary is started by Renode. The interprocess communication is based on sockets.

How to make your own ‘verilated’ peripheral

An example ‘verilated’ UARTLite model is available on Antmicro’s GitHub.

To make your own ‘verilated’ peripheral, in the main cpp file of your verilated model you need to include C++ headers applicable to the bus you are connecting to and the type of external interfaces you want to integrate with Renode – e.g. UART’s rx/tx signals. These headers can be found in the integration library.

// uart.h and axilite.h can be found in Renode's VerilatorPlugin
#include "src/peripherals/uart.h"
#include "src/buses/axilite.h"

Next, you will need to define a function that will call your model’s eval function, and provide it as a callback to the integration library struct, along with bus and peripheral signals.

void eval() {
#if VM_TRACE
  main_time++;
  tfp->dump(main_time);
#endif
  top->eval();
}

void Init() {
  AxiLite* bus = new AxiLite();

  //==========================================
  // Init bus signals
  //==========================================
  bus->clk = &top->clk;
  bus->rst = &top->rst;
  bus->awaddr = (unsigned long *)&top->awaddr;
  bus->awvalid = &top->awvalid;
  bus->awready = &top->awready;
  bus->wdata = (unsigned long *)&top->wdata;
  bus->wstrb = &top->wstrb;
  bus->wvalid = &top->wvalid;
  bus->wready = &top->wready;
  bus->bresp = &top->bresp;
  bus->bvalid = &top->bvalid;
  bus->bready = &top->bready;
  bus->araddr = (unsigned long *)&top->araddr;
  bus->arvalid = &top->arvalid;
  bus->arready = &top->arready;
  bus->rdata = (unsigned long *)&top->rdata;
  bus->rresp = &top->rresp;
  bus->rvalid = &top->rvalid;
  bus->rready = &top->rready;

  //==========================================
  // Init eval function
  //==========================================
  bus->evaluateModel = &eval;

  //==========================================
  // Init peripheral
  //==========================================
  uart = new UART(bus, &top->txd, &top->rxd,
  prescaler);
}

As part of the last step, in the main function, you have to call simulate, providing it with port numbers, which are passed as the first two command-line arguments of the resulting binary.

Init();
uart->simulate(atoi(argv[1]), atoi(argv[2]));

Now you can compile your project with Verilator:

verilator -cc top.v --exe -CFLAGS "-Wpedantic -Wall -I$(INTEGRATION_DIR)" sim_main.cpp $(INTEGRATION_DIR)/src/renode.cpp $(INTEGRATION_DIR)/src/buses/axilite.cpp $(INTEGRATION_DIR)/src/peripherals/uart.cpp

make -j 4 -C obj_dir -f Vtop.mk

The resulting simulation can be attached to the Renode platform and used in a .repl file as a ‘verilated’ peripheral.

uart: Verilated.VerilatedUART @ sysbus <0x70000000, +0x100>
  simulationFilePath: @verilated_simulation_file_path
  frequency: 100000000

When you load such a platform in Renode and run a sample application, this is the output you’ll see. Keep in mind that the UART window displays data printed by the verilated peripheral.

You can also enable signal trace dumping by setting the VERILATOR_TRACE=1 variable in your shell. The resulting trace is written into a vcd file and can be viewed in e.g. GTKWave viewer.

Renode’s powerful co-simulation capabilities

Whether you are working on a new hardware block or you want to reuse the HDL code you have, Renode’s co-simulation capabilities allow you to test your IP in a broader context than just usual hardware simulation, connecting it to entire RISC-V, ARM or other SoCs even without writing any model.

You can use Renode’s powerful tracing and logging mechanisms to observe your peripheral’s behavior when used by an operating system of your choice, in an environment of your choice – be it a full-blown Linux-capable multi-core system or a small RTOS-ready SoC, or even a mix of those options.

Want to debug your driver via GDB but your target FPGA does not have a debugger connector? Or maybe it is just too small to contain the whole SoC you’d like to run? Perhaps you’d like to run a Python script to create a nice graph on each peripheral access? Renode has got you covered with all these features available out of the box.

If this sounds interesting, you can start using Renode’s co-simulation capabilities today or let us know about your use case directly so that we can potentially help you improve your simulation-driven workflow – all you need to do is get back to us at contact@renode.io.

If you’re new to Zephyr RTOS, please see our Getting Started Guide and check out our Contributor Guide. Or, you can join the conversation and ask questions on our Slack channel or Mailing List and follow #zephyrproject on IRC.