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Circle

Overview

Circle is a C++ bare metal programming environment for the Raspberry Pi. It should be usable on all existing models (tested on model A+, B, B+, on Raspberry Pi 2, 3, 4, 400, 5 and on Raspberry Pi Zero), except on the Raspberry Pi Pico, which is not supported. Circle provides several ready-tested C++ classes and add-on libraries, which can be used to control different hardware features of the Raspberry Pi. Together with Circle there are delivered several sample programs, which demonstrate the use of its classes. Circle can be used to create 32-bit or 64-bit bare metal applications.

Circle includes bigger (optional) third-party C-libraries for specific purposes in addon/ now. This is the reason why GitHub rates the project as a C-language-project. The main Circle libraries are written in C++ using classes instead. That's why it is called a C++ programming environment.

The 47th Step

This release provides a number of new features for the Raspberry Pi 5, which were already available for earlier models:

• SPI master support (polling and DMA driver)
• I2S sound (output or input, DMA or programmed I/O operation)
• PWM sound (requires external circuit on GPIO12/13 or GPIO18/19)
• PWM output (4 channels)
• GPIO clocks (GP0-2)
• CGPIOPin::WriteAll() and CGPIOPin::ReadAll()

The following new hardware features of the Raspberry Pi 5 are supported now:

• Real-time clock (class CFirmwareRTC in addon/rtc)
• Power button (Function is_power_button_pressed())
• Function main() can return EXIT_POWER_OFF to power-off the system
• 8-channels I2S sound output (via GPIO21/23/25/27, e.g. for HifiBerry DAC8x)

The WM8960 I2S sound driver has been revised and provides a better audio quality and the sound controller jack and control functions now. The new sound controller control ControlALC (Automatic Level Control) has been defined and implemented for the WM8960. ALC is disabled by default now. The WM8960 driver supports sample rates of 44100 and 48000.

More news:

• A new IRQ-based driver for the I2C master of Raspberry Pi 1-4 is available.
• A character mode for ST7789-based dot-matrix displays is available.
• The timing of the GPIO pin driver has been improved on the Raspberry Pi 5 by using the RIO module.
• There is a new GPIO pin mode GPIOModeNone, which disables the GPIO pin on the Raspberry Pi 5. On other models it has the same function as GPIOModeInput.
• The new static method CGPIOPin::SetModeAll() allows to set the mode of the GPIO pins 0-31 at once to input or output.
• IP multi-cast support level 1 according to RFC 1112 is implemented (send only).
• The LVGL support has been updated to LVGL v8.3.11.

Fixes:

• The USB serial CDC gadget was not detected on Windows 10.
• The Raspberry Pi Debug Probe UART did not work with the USB serial CDC driver.
• The class CPWMSoundDevice did not apply the full chunk size.

The recommended firmware and toolchain versions have been updated.

Features

Only the features with a "x" or other info are currently supported on the Raspberry Pi 5.

Circle supports the following features:

Building

For building 64-bit applications (AArch64) see the next section.

Circle does not support 32-bit applications on the Raspberry Pi 5.

This describes building on PC Linux. See the file doc/windows-build.txt for information about building on Windows. If building for the Raspberry Pi 1 you need a toolchain for the ARM1176JZF core (with EABI support). For Raspberry Pi 2/3/4 you need a toolchain with Cortex-A7/-A53/-A72 support. A toolchain, which works for all of these, can be downloaded here. Circle has been tested with the version 13.2.Rel1 (arm-gnu-toolchain-13.2.rel1-x86_64-arm-none-eabi.tar.xz) from this website. This is the recommended toolchain for AArch32 builds.

First edit the file Rules.mk and set the Raspberry Pi version (RASPPI, 1, 2, 3 or 4) and the PREFIX of your toolchain commands. Alternatively you can create a Config.mk file (which is ignored by git) and set the Raspberry Pi version and the PREFIX variable to the prefix of your compiler like this (don't forget the dash at the end):

RASPPI = 1
PREFIX = arm-none-eabi-

The following table gives support for selecting the right RASPPI value:

For a binary distribution you should do one build with RASPPI = 1, one with RASPPI = 2 and one build with RASPPI = 4 and include the created files kernel.img, kernel7.img and kernel7l.img. Optionally you can do a build with RASPPI = 3 and add the created file kernel8-32.img to provide an optimized version for the Raspberry Pi 3.

The configuration file Config.mk can be created using the configure tool too. Please enter ./configure -h for help on using it!

There are a number of configurable system options in the file include/circle/sysconfig.h. Please have a look into this file to learn, how you can configure Circle for your purposes. Some hardware configurations may require modifications to these options (e.g. using USB on the CM4).

Then go to the build root of Circle and do:

./makeall clean
./makeall

By default only the Circle libraries are built. To build a sample program after makeall go to its subdirectory and do make.

You can also build Circle on the Raspberry Pi itself (set PREFIX = (empty)) on Raspbian but you need some method to put the kernel.img file onto the SD(HC) card. With an external USB card reader on model B+ or Raspberry Pi 2/3/4 model B (4 USB ports) this should be no problem.

AArch64

Circle supports building 64-bit applications, which can be run on the Raspberry Pi 3, 4 or 5. There are also Raspberry Pi 2 versions and the Raspberry Pi Zero 2, which are based on the BCM2837 SoC. These Raspberry Pi versions can be used too (with RASPPI = 3).

The recommended toolchain to build 64-bit applications with Circle can be downloaded here. Circle has been tested with the version 13.2.Rel1 (arm-gnu-toolchain-13.2.rel1-x86_64-aarch64-none-elf.tar.xz) from this website. This is the recommended toolchain for AArch64 builds.

There are distro-provided toolchains on certain Linux platforms (e.g. g++-aarch64-linux-gnu on Ubuntu or gcc-c++-aarch64-linux-gnu on Fedora), which may work with Circle and can be a quick way to use it, but you have to test this by yourself. If you encounter problems (e.g. no reaction at all, link failure with external library) using a distro-provided toolchain, please try the recommended toolchain (see above) first, before reporting an issue.

First edit the file Rules.mk and set the Raspberry Pi architecture (AARCH, 32 or 64) and the PREFIX64 of your toolchain commands. The RASPPI variable has to be set to 3, 4 or 5 for AARCH = 64. Alternatively you can create a Config.mk file (which is ignored by git) and set the Raspberry Pi architecture and the PREFIX64 variable to the prefix of your compiler like this (don't forget the dash at the end):

AARCH = 64
RASPPI = 3
PREFIX64 = aarch64-none-elf-

The configuration file Config.mk can be created using the configure tool too. Please enter ./configure -h for help on using it!

Then go to the build root of Circle and do:

./makeall clean
./makeall

By default only the Circle libraries are built. To build a sample program after makeall go to its subdirectory and do make.

Installation

Copy the Raspberry Pi firmware (from boot/ directory, do make there to get them) files along with the kernel*.img (from sample/ subdirectory) to a SD(HC) card with FAT file system.

It is now always recommended to copy the file config32.txt (for 32-bit mode) or config64.txt (for 64-bit mode) from the boot/ directory to the SD(HC) card and to rename it to config.txt there. These files are especially required to enable FIQ use on the Raspberry Pi 4. Furthermore the additional file armstub7-rpi4.bin (for 32-bit mode) or armstub8-rpi4.bin (for 64-bit mode) is required on the SD card then. Please see boot/README for information on how to build these files.

Finally put the SD(HC) card into the Raspberry Pi.

Directories

• include: The common header files, most class headers are in the include/circle/ subdirectory.
• lib: The Circle class implementation and support files (other libraries are in subdirectories of lib/).
• sample: Several sample applications using Circle in different subdirectories. The main function is implemented in the CKernel class.
• addon: Contains contributed libraries and samples (has to be build manually).
• app: Place your own applications here. If you have own libraries put them into app/lib/.
• boot: Do make in this directory to get the Raspberry Pi firmware files required to boot.
• doc: Additional documentation files.
• test: Several test programs, which test different features of Circle.
• tools: Tools for building Circle and for using Circle more comfortable (e.g. a serial bootloader).

Classes

The following C++ classes were added to Circle:

Base library

• CDMAChannelRP1: RP1 platform DMA controller support (for Raspberry Pi 5)
• CI2CMasterIRQ: Driver for I2C master devices (asynchronous using IRQ, for Raspberry Pi 1-4)

The available Circle classes are listed in the file doc/classes.txt. If you have Doxygen installed on your computer you can build a class documentation in doc/html/ using:

./makedoc

At the moment there are only a few classes described in detail for Doxygen.

Additional Topics

• Standard library support
• Dynamic memory management and the "new" operator
• DMA buffer requirements
• Serial bootloader support
• Multi-core support
• USB plug-and-play
• Debugging support
• JTAG debugging
• QEMU support
• Eclipse IDE support
• About real-time applications
• cmdline.txt options
• Screen escape sequences
• Keyboard escape sequences
• Clang support
• Memory layout
• Naming conventions
• Known issues

Trademarks

Raspberry Pi is a trademark of Raspberry Pi Ltd.

Linux is a trademark of Linus Torvalds.

PS3 and PS4 are registered trademarks of Sony Computer Entertainment Inc.

Windows, Xbox 360 and Xbox One are trademarks of the Microsoft group of companies.

Nintendo Switch is a trademark of Nintendo.

Khronos and OpenVG are trademarks of The Khronos Group Inc.

OpenGL ES is a trademark of Silicon Graphics Inc.

The micro:bit brand belongs to the Micro:bit Educational Foundation.

HDMI is a registered trademark of HDMI Licensing Administrator, Inc.