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samd20-gcc-blackmagic

A simple GCC setup for Atmel SAM D20 development, intended for use with the blackmagic debug probe.

Prerequisites

GNU Make and the following standard utilities are required: cat, echo, find, grep, mkdir, rm, sed and tr. If you're running any sensible desktop linux then these will already be installed.

You will also need to aquire GNU Tools for ARM Embedded Processors.

On Ubuntu
sudo add-apt-repository ppa:terry.guo/gcc-arm-embedded
sudo apt-get update && sudo apt-get install gcc-arm-none-eabi
Note about gcc-arm-embedded on Ubuntu 14.04 and later

If you are using Ubuntu 14.04 and later, please be careful because there are packages with same name but produced by Debian and inherited by Ubuntu. Simply follow the above 3 steps, you may end up with gcc-arm-none-eabi from Ubuntu. So to install gcc-arm-none-eabi from ARM, steps are:

1). sudo apt-get remove binutils-arm-none-eabi gcc-arm-none-eabi
2). sudo add-apt-repository ppa:terry.guo/gcc-arm-embedded
3). sudo apt-get update
4). sudo apt-get install gcc-arm-none-eabi=4-8-2014q2-0trusty10

Meanwhile we are working with Debian to consolidate and unify this toolchain.

Usage

Project Options

config.mk allows configuation for individual projects. In particular the PROJECT_NAME and TARGET_CHIP variables needs to be set.

Compiling

make

Backmagic

Download

Run arm-none-eabi-gdb. If you have set BLACKMAGIC_PATH in config.mk then gdb will attempt to connect to the blackmagic debugger. Otherwise you can use the blackmagic command to connect a /dev/ttyACM<n> device. For example blackmagic 0 will connect to a blackmagic at /dev/ttyACM0.

To attach to the SAM D20 chip itself you will need to run something like

monitor swdp_scan
attach 1

You can place these commands in a gdbscript-custom file so that in future they will be run automatically. If monitor swdp_scan fails to detect an attached SAM D20 device then you may need to upgrade the firmware on your blackmagic to the latest version.

To download code run

monitor erase_mass
load

Debugging

You can start with the gdb command

run

You might want to use the command set confirm off so that you're not prompted each time. You might also want to set mem inaccessible-by-default off so that you can look at memory locations outside of RAM and ROM.

These commands can be automated by placing them in a gdbscript-custom file.

Semihosting

You can build for semihosting by defining the SEMIHOSTING variable in make. Like this:

make -kB SEMIHOSTING=1

This build will be significantly larger (in terms of RAM and ROM).

For this build, when a debugger is present at startup the semihost_printf, semihost_puts and semihost_putchar functions will print to stdio on the host. The Blackmagic Debug Probe supports this.

Emacs

The command make emacs can be used to quickly launch an instance of emacs with all the relavent source code loaded.

A TAGS file can be generated with make all or make tags, and this can be used to automat navigate the source code. See the emacs manual for more details.

A Directory Local Variables File .dir-locals.el exists in the root of the project. This has the following effects on emacs:

Fixed default-directory

The default directory is fixed as the root of the project wherever you are within the project. As the makefile needs to be run from the root of the project, this means that M+x compile will always run the top-level makefile no matter which file you are editing.

Custom GDB

M+x gdb is set to use arm-none-eabi-gdb rather than the default GDB for your machine.

Other notes

Wherever possible use Function Attributes and Variable Attrubutes rather than editing the project's linker files.

Sources & Licensing

See LICENSE.md

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