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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:

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

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:

Fixes:

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:

GroupFeaturesRaspberry Pi 5
C++ build environmentAArch32 and AArch64 supportAArch64 only
Basic library functions (e.g. new and delete)x
Enables all CPU caches using the MMUx
Interrupt support (IRQ and FIQ)IRQ only
Multi-core support (Raspberry Pi 2, 3 and 4)x
Cooperative non-preemtive schedulerx
CPU clock rate managementx
Clang/LLVM support (experimental)x
Debug supportKernel logging to screen, UART and/or syslog serverx
C-assertions with stack tracex
Hardware exception handler with stack tracex
GDB support using rpi_stub (Raspberry Pi 2 and 3)
Serial bootloader (by David Welch) includedx
Software profiling support (single-core)x
QEMU support
SoC devicesGPIO pins (with interrupt, Act LED) and clocksx
Frame buffer (screen driver with escape sequences)limited
UART(s) (Polling and interrupt driver)x
System timer (with kernel timers)x
Platform DMA controllerDMA40 only
RP1 platform DMA controller (Raspberry Pi 5 only)x
EMMC SD card interface driverx
SDHOST SD card interface driver (Raspberry Pi 1-3)
PWM output (2 channels)4 channels
PWM sound output (on headphone jack)with adapter
I2C master(s) and slavemasters only
SPI0 master (Polling and DMA driver)x
SPI1 auxiliary master (Polling)
SPI3-6 masters of Raspberry Pi 4 (Polling)SPI1-3 and 5
SMI master (experimental)
I2S sound output and inputx
HDMI sound output (without VCHIQ)
Hardware random number generatorx
Watchdog devicex
Official Raspberry Pi touch screen
VCHIQ interface and audio service drivers
BCM54213PE Gigabit Ethernet NIC of Raspberry Pi 4
MACB / GEM Gigabit Ethernet NIC of Raspberry Pi 5x
Wireless LAN accessx
USBHost controller interface (HCI) driversx
Standard hub driver (USB 2.0 only)x
HID class device drivers (keyboard, mouse, gamepad)x
Driver for on-board Ethernet device (SMSC951x)
Driver for on-board Ethernet device (LAN7800)
Driver for USB mass storage devices (bulk only)x
Driver for USB audio streaming devices (RPi 4 only)x
Drivers for different USB serial devicesx
Audio class MIDI input supportx
Touchscreen driver (digitizer mode)x
Printer driverx
MIDI gadget driver
Serial CDC gadget driver (experimental)
File systemsInternal FAT driver (limited function)x
FatFs driver (full function, by ChaN)x
TCP/IP networkingProtocols: ARP, IP, ICMP, UDP, TCPx
Clients: DHCP, DNS, NTP, HTTP, Syslog, MQTTx
Servers: HTTP, TFTPx
BSD-like C++ socket APIx
GraphicsOpenGL ES 1.1 and 2.0, OpenVG 1.1, EGL 1.4
(not on Raspberry Pi 4)
uGUI (by Achim Doebler)
LVGL (by LVGL Kft)x
2D graphics class in base library
Not supportedBluetooth

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:

RASPPITargetModelsOptimized for
1kernel.imgA, B, A+, B+, Zero, (CM)ARM1176JZF-S
2kernel7.img2, 3, Zero 2, (CM3)Cortex-A7
3kernel8-32.img3, Zero 2, (CM3)Cortex-A53
4kernel7l.img4B, 400, CM4Cortex-A72

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

Classes

The following C++ classes were added to Circle:

Base library

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

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.