This is Step 22 of Circle. To get access to Step 1-21 use the git tag "Step1" to "Step21".

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Circle is a C++ bare metal programming environment for the Raspberry Pi. It should be useable on all existing models (tested on model A+, B, B+, on Raspberry Pi 2 and on Raspberry Pi Zero). It provides several ready-tested C++ classes which can be used to control different hardware features of the Raspberry Pi. Together with Circle there are delivered some samples which demonstrate the use of its classes.

Please note that the included USB library was developed in a hobby project. There are known issues with it (e.g. no dynamic attachments, no error recovery, limited split support). For me it works well but that need not be the case with any device and in any situation.

Circle is not a real-time OS. That means different simultaneous operations may interfere in respect of its timing behaviour. The provided samples are tested to work but if you try different combinations of hardware support classes this has to be tested by yourself.

A known issue here is that the use of USB interrupt split transfers - especially used by USB keyboard and mouse - will drop the interrupt response time to about one millisecond at worst.

In this step some basic Bluetooth support is added to Circle and demonstrated in a simple Bluetooth Inquiry (device search) sample in sample/22-btsimple. You need an USB Bluetooth BR/EDR dongle to use this sample. See the README file in this directory for details.

Single-core Circle applications can be source-level debugged on the Raspberry Pi 2 using the GNU debugger (GDB) and rpi_stub now. See doc/debug.txt for details.

The options to be used for cmdline.txt are described in doc/cmdline.txt.

In Step 1-21 the following features were introduced:

• C++ build environment
• Simple delay functionality
• Get properties (model, memory size) from VideoCore
• new and delete
• Using GPIO pins
• Manipulating Act LED
• Set pixel on screen
• Use kernel options
• Switch on MMU
• Formatting strings
• Using devices
• Writing characters to screen
• Writing characters to UART
• Logging output to screen or UART
• Using assertions and debug hexdump
• Using interrupts
• Timer class with clock, timers and calibrated delay loop
• Exception handler
• USB host controller interface (HCI) driver (no split support for now)
• USB device class (basic device initialization)
• USB hub driver (dectects and enables the supported devices)
• Driver for the on-board Ethernet device (receiving and transmitting frames)
• Driver for USB mass storage devices (bulk only, read and write)
• Detects low- and full-speed devices
• Driver for USB keyboards
• Using GPIO interrupts
• Driver for USB mice
• Using GPIO clock
• Simple 12 MHz GPIO sampling routine
• PWM sound device
• DMA controller support
• PWM output (2 channels)
• Simple USB printer support
• FAT file system support (reduced)
• I2C (master and slave) support
• Multi-core support on Raspberry Pi 2
• Experimental (UDP only) TCP/IP network stack
• Setting system time from an Internet time (NTP) server
• Cooperative non-preemtive scheduler
• TCP support
• DHCP support
• Simple HTTP webserver class
• GDB debug support on Raspberry Pi 2 using rpi_stub

Building is normally done on PC Linux. If building for the Raspberry Pi 1 you need a toolchain for the ARM1176JZF core. For Raspberry Pi 2 you need a toolchain with Cortex-A7 support. This one should work for both.

First edit the file Rules.mk and set the Raspberry Pi version (RASPPI, 1 or 2) 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-

Then go to the build root of Circle and do:

./makeall clean
./makeall

By default only the latest sample (with the highest number) is build. The ready build kernel.img file should be in its subdirectory of sample/. If you want to build another sample after makeall go to its subdirectory and do make.

You can also build Circle on the Raspberry Pi itself 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 model B (4 USB ports) this should be no problem.

Building Circle from a non-Linux host is possible too. Maybe you have to adapt the shell scripts in this case. You need a cross compiler targetting (for example) arm-none-eabi. OSDev.org has an excellent document on the subject that you can follow if you have no idea of what a cross compiler is, or how to make one.

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. Put the SD(HC) card into the Raspberry Pi.

Note that the file kernel.img can be renamed to kernel7.img for the Raspberry Pi 2 but this is optional.

• 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).
• boot: Do make in this directory to get the Raspberry Pi firmware files required to boot.
• doc: Additional documentation files.

The following C++ classes were added to Circle:

Bluetooth library

• CBTDeviceManager: Manages the local Bluetooth device. Part of the HCI layer.
• CBTHCILayer: Bluetooth HCI layer. Basic communication with the local Bluetooth controller.
• CBTInquiryResults: Container for the responses of an Inquiry operation.
• CBTLogicalLayer: Bluetooth logical layer. Handles Inquiry operation only at the moment.
• CBTQueue: Encapsulates a queue used for incoming and outgoing command, event and data packets.
• CBTSubSystem: The main Bluetooth subsystem class. Create an instance of it in the CKernel class.
• CBTTask: Bluetooth background task. Processes the different Bluetooth layers.

USB library

• CUSBBluetoothDevice: Bluetooth HCI transport driver for USB Bluetooth BR/EDR dongles.

The available Circle classes are listed in the file doc/classes.txt.