emgo

Emgo

Emgo consist of a compiler and the set of packages that allows you to run Go programs on small 32-bit microcontrollers. The compiler generates C as an intermediate code and uses C compiler to produce loadable binaries.

There is Embedded Go project that evolved from Emgo which is based on the reference Go compiler. It has much higher hardware requirements but it is also 100% compatible with the Go language specification. The main development process has moved to Embeadded Go but I still use Emgo for small MCUs so some things can be backported here.

How to start

First of all, to try Emgo you need the Go compiler installed. The current Emgo compiler and whole process described below requires also some kind of Unix-like operating system. There is a chance that Windows with Cygwin can be used but this was not tested.

You can probably use go get to install Emgo but the preferred way is to clone this repository using the git command:

git clone https://github.com/ziutek/emgo.git

Next you need to build and install egc (Emgo compiler):

cd emgo/egc
go install

For now, Emgo supports only ARM Cortex-M based MCUs. To build code for Cortex-M architecture, you need to install ARM embedded toolchain. You have two options: install a package included in your OS distribution (in case of Debian/Ubuntu Linux):

apt-get install gcc-arm-none-eabi

or better go to the GNU ARM Embedded Toolchain website and download most recent toolchain. This is preferred version of toolchain, try use it before report any bug with compilation.

Installed toolchain contains set of arm-none-eabi-* binaries. Find their location and set required enviroment variables:

export EGCC=path_to_arm_gcc            # eg. /usr/local/arm/bin/arm-none-eabi-gcc
export EGLD=path_to_arm_linker         # eg. /usr/local/arm/bin/arm-none-eabi-ld
export EGAR=path_to_arm_archiver       # eg. /usr/local/arm/bin/arm-none-eabi-ar

export EGROOT=path_to_egroot_directory # eg. $HOME/emgo/egroot
export EGPATH=path_to_egpath_directory # eg. $HOME/emgo/egpath

Load/debug helper scripts use also some other tools from the ARM toolchain (eg. arm-none-eabi-objcopy). If you downloaded the toolchain manually, you probably need also to add its bin directory to the PATH enviroment variable:

export PATH=$PATH:path_to_arm_bin_dir  # eg. /usr/local/arm/bin

Now you are ready to compile some example code. There are two directories that contain examples:

$EGPATH/src/stm32/examples

$EGPATH/src/nrf5/examples

Use one that contains example for your MCU/devboard.

For example, to build blinky for STM32 NUCLEO-F411RE board:

cd $EGPATH/src/stm32/examples/nucleo-f411re/blinky
../build.sh

The first compilation may take some time because egc must process all required libraries and runtime. If everything went well you obtain cortexm4f.elf binary file.

Compilation can produce two kind of binaries: binaries that should be loaded to RAM or loaded to Flash of your MCU.

Loading to RAM is useful in case of small programs, during working on the code and debuging. Loading to RAM is faster, allows unlimited number of breakpoints, allows to modify constants and even the code from debuger and saves your Flash, which has big but limited number of erase cycles.

To run program loaded to RAM you must change the MCU boot behavior. In case of most STM32 MCUs you simply need to set high BOOT0 and BOOT1 pins. Newer STM32 MCUs do not provide BOOT1 pin, insdead they require to program some persistant bits that change the default booting behavior when BOOT0 is set high.

However, eventually your program should be loaded to Flash. Sometimes you have no other alternative: your program is too big to fit into RAM or your MCU does not provide easy way to run program from RAM (eg. nRF51). Some bugs may only appear when the program runs from Flash or from RAM, so it is advisable to perform the final test of any new piece of code in both ways.

You need tools to load compiled binary to your MCU's RAM/Flash and allow to debug it. Such tools usually have a hardware part and a software part. In case of STM32 Nucleo or Discovery development boards the hardware part (ST-LINK programmer) is integrated with the board, so you only need the software part, which can be OpenOCD or Texane's stlink. You must install one of them or both before next steps (ensure that openocd and/or st-util binaries are on your PATH).

There is a set of scripts for any board in example directory that simplifies loding and debuging process. The load-oocd.sh and swo-oocd.sh scripts can handle SWO output from ITM (Instrumentation Trace Macrocell) but needs itmsplit to convert binary stream to readable messages. SWO is very useful for debuging and fmt.Print* functions by default use ITM trace port as standard output. Install itmsplit with the command:

go get github.com/ziutek/itmsplit

and ensure that produced binary is in your PATH.

You need the rights to the USB device that corresponds to your programming hardware. This can be done through adding appropriate udev rules. See example rules in Texane's stlink repository, in etc directory.

To program your MCU using Texane's stlink run:

../load-stutil.sh

If you want to use OpenOCD, run:

../load-oocd.sh

Some examples by default are configured to run from RAM. If you have problem to setup your board to run from RAM, edit script.ld file and change the line:

INCLUDE stm32/loadram

to

INCLUDE stm32/loadflash

More editing is need for STM32F1xx series: you additionally have to comment two lines:

bootOffset = 0x1E0;
ENTRY(bootRAM)

You can also load your program during debug session in gdb. Run ../debug-stutil.sh or ../debug-oocd.sh and next invoke load command.

There are also scripts for Black Magic Probe: load-bmp.sh, debug-bmp.sh.

If you played with examples and enjoyed Emgo you probably want to write your first program from scratch, compile it and load without all these magical scripts. This blog post presents how to do it.

You may encounter a problem where st-util or openocd can not connect to your board. This is often the case for boards without integrated programmer/debuger, when the external programmer has no connection to the reset pin. If you can not make such connection, simply press and hold the reset button on your board, next run load/debug script and after the script finishes printing anything, release the reset.

Documentation

Standard library

Libraries for STM32, nRF5 and other

Other resources

Blog

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