Tock Userland

This directory contains libraries and example applications for developing Tock apps that sit above the kernel.

Prerequisites

If you have not yet done so, it might be a good idea to start with the TockOS getting started guide, which will lead you through the installation of some tools that will be useful for developing and deploying applications on TockOS. In particular, it will give you a rust environment (required to install elf2tab) and tockloader, which you need to deploy applications on most boards.

And it will of course give you a board with TockOS installed which you can use to run the applications found in this repository.

So, if you haven't been there before, just head over there until it sends you back here.

Clone this repository.

$ git clone https://github.com/tock/libtock-c
$ cd libtock-c

The main requirement to build the C applications in this repository is having cross compilers for embedded targets. You will need an arm-none-eabi toolchain for Cortex-M targets.

MacOS:
```
$ brew tap ARMmbed/homebrew-formulae && brew update && brew install arm-none-eabi-gcc
```
Ubuntu (18.04LTS or later):
```
$ sudo apt install gcc-arm-none-eabi
```
Arch:
```
$ sudo pacman -Syu arm-none-eabi-gcc
```
Optional: libtock-c also includes support for building for RISC-V targets. These are not included by default since obtaining the toolchain can be difficult (as of June 2020). You will need a riscv64-unknown-elf GCC toolchain that supports rv32 targets as well (i.e. is compiled with multilib support).

To actually build for the RISC-V targets, add RISCV=1 to the make command:
```
$ make RISCV=1
```
MacOS:
```
$ brew tap riscv/riscv && brew update && brew install riscv-gnu-toolchain --with-multilib
```
Warning: this will compile from source, and takes a while. Also this will build a bleeding-edge version of GCC, and there is a small chance it will not work. However, we have successfully obtained a toolchain this way.

Ubuntu (19.10 or later):
```
$ sudo apt install gcc-riscv64-unknown-elf
```
Unfortunately, Ubuntu does not currently (June 2020) provide a package for RISC-V libc. We have created a .deb file you can use to install a suitable libc based on newlib:
```
$ wget http://cs.virginia.edu/~bjc8c/archive/newlib_3.3.0-1_amd64.deb
$ sudo dpkg -i newlib_3.3.0-1_amd64.deb
```
If you would rather compile your own newlib-based libc, follow the steps below. Section [newlib-nano][newlib-nano] describes some extra config options to build a size optimised newlib.
```
# Download newlib 3.3 from https://sourceware.org/newlib/
wget ftp://sourceware.org/pub/newlib/newlib-3.3.0.tar.gz
tar -xvf newlib-3.3.0.tar.gz
cd newlib-3.3.0
# Disable stdlib for building
export CFLAGS=-nostdlib
# Run configure
./configure --disable-newlib-supplied-syscalls --with-gnu-ld --with-newlib --enable-languages=c --target=riscv64-unknown-elf --host=x86 --disable-multi-lib --prefix /usr
# Build and then install
make -j8
sudo make install
```
Alternatively, you may use a pre-compiled toolchain that we created with Crosstool-NG.
```
$ wget http://cs.virginia.edu/~bjc8c/archive/gcc-riscv64-unknown-elf-8.3.0-ubuntu.zip
$ unzip gcc-riscv64-unknown-elf-8.3.0-ubuntu.zip
# add gcc-riscv64-unknown-elf-8.3.0-ubuntu/bin to your `$PATH` variable.
```
Arch:
```
$ sudo pacman -Syu riscv64-elf-gcc riscv32-elf-newlib
```
newlib-nano:

newlib can require a large amount of memory, espicially for printing. If this is a concern you can instead use a more size optimised version. As of August 2020 there are a few options for this. * See if the version of newlib from your distro already has the flags below enabled. If it does it's already size optimsed. * See if your distro pacakges a newlib-nano (Debian does this) that will already include the flags below. * See if your distro packages picolibc, which is a optimised fork of newlib. * You can compile newlib with these extra flags: --enable-newlib-reent-small \ --disable-newlib-fvwrite-in-streamio \ --disable-newlib-fseek-optimization \ --disable-newlib-wide-orient \ --enable-newlib-nano-malloc \ --disable-newlib-unbuf-stream-opt \ --enable-lite-exit \ --enable-newlib-global-atexit \ --enable-newlib-nano-formatted-io
You will also need an up-to-date version of elf2tab. The build system will install and update this automatically for you, but you'll need Rust's cargo installed. If you have followed the getting started guide, everything should be in place.
You will also likely need Tockloader, a tool for programming apps onto boards. If you haven't installed it during the TockOS getting started guide:

MacOS:
```
$ pip3 install tockloader
```
Ubuntu:
```
$ pip3 install tockloader --user
```

Compiling and Running Applications

To compile all the examples, switch to the examples directory and execute the build script:

$ cd examples
$ ./build_all.sh

This will install elf2tab if it is not yet installed and compile all the examples for cortex-m0, cortex-m3, cortex-m4, and rv32imac. It does this because the compiler emits slightly (or significantly) different instructions for each variant. When installing the application, tockloader will select the correct version for the architecture of the board being programmed.

The build process will ultimately create a tab file (a "Tock Application Bundle") for each example application. The tab contains the executable code for the supported architectures and can be deployed to a board using tockloader. For example to one of the Nordic development boards:

$ tockloader install --board nrf52dk --jlink blink/build/blink.tab
Installing apps on the board...
Using known arch and jtag-device for known board nrf52dk
Finished in 2.567 seconds

You can remove an application with

$ tockloader uninstall --board nrf52dk --jlink blink

or remove all installed applications with

$ tockloader uninstall --board nrf52dk --jlink

Tock applications are designed to be generic and run on any Tock-compatible board. However, compiled applications typically depend on specific drivers, which not all boards provide. For example, some applications expect an IEEE 802.15.4 radio interface which not all boards support. If you load an application onto a board that does not support every driver/system call it uses, some system calls will return error codes (ENODEVICE or ENOSUPPORT).

Next Steps

The next step is to read the overview that describes how applications in TockOS are structured and then look at some of the examples in detail. The description of the compilation environment may also be of interest.

License

Licensed under either of

Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contributions

We welcome contributions from all. We use the bors-ng bot to manage, approve, and merge PRs. In short, when someone replies bors r+, your PR has been approved and will be automatically merged. If a maintainer replies bors delegate+, then you have been granted the authority to mark your own PR for approval (usually this will happen if there are some trivial changes required). For a full list of bors commands, see the bors documentation.