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Getting started with STM8 development using free software: Benchmarks on the NUCLEO-8L152R8

This short tutorial shows how to compile the stdcbench and Whetstone benchmarks and execute them on an STMicroelectronics NUCLEO-8L152R8 board. The popular Dhrystone benchmark requires about 5KB of RAM, and is thus not suitable for the NUCLEO-8L152R8 which uses an STM8L152R8 that has 4 KB of RAM. The non-free Coremark is not explicitly discussed here, but can be made to work on the NUCLEO-8L152R8 similar to stdcbench and Whetstone. The author used a Debian GNU/Linux system, but the tutorial should work for other Linux distributions, *BSD or other Unices.

The tools we use are

Hardware setup


The NUCLEO-8L152R8 is connected to the host computer via a USB cable for power and to write the demo onto the board using the integrated ST-LINK/V2-1. We connect the serial cable to ground and data at CN9 (black to pin 20, white to pin 25, green to pin 27).


Depending on your operating system there might be an easy way to install SDCC 3.5.0 or newer using a package system or similar (e.g. apt-get install sdcc on Debian). While SDCC 3.4.0 should be sufficient for this tutorial, you might want to try a newer version in case you encounter any bugs. In particular, SDCC 3.4.0 has an issue with the library search path; this can be worked around by explicitly specifying the path to the standard library when linking.

SDCC binaries or a source tarball can be downloaded from its website.

Get stm8flash

The stm8flash source can be found at its GitHub location, where there is also a download link for a zip archive of the sources. To compile it, a C compiler, such as gcc, pkg-config and libusb need to be installed. Unzip the archive (e.g. using unzip change into the directory stm8flash-master and type make. In case there are any errors, such as header files not found, check that pkg-config and development files for libusb are installed.

Get stdcbench

Download an stdcbench release tarball from its website.
Download, and unpack it using e.g. tar -xzf stdcbench-0.6.tar.gz, change into the directory stdcbench-0.6.
You can then compile stdcbench by typing make -f examples/Makefile.SDCC-STM8LNUCLEO. In the end there should be a file stdcbench.ihx.

The custom code was necessary to make stdcbench run using SDCC on the NUCLEO-8L152R8 can be found in the files file examples/portme.h.SDCC-STM8LNUCLEO and examples/portme.c.SDCC-STM8LNUCLEO. The file examples/portme.c.SDCC-STM8LNUCLEO basically combines clock() from the timer demo and putchar() from the serial demo.

Put stdcbench onto the board

Assuming stm8flash and serial.ihx are in the same directory, the board is attached through the integrated stlinkv21 device, ./stm8flash -c stlinkv21 -p stm8l152r8 -w stdcbench.ihx will write stdcbench onto the board. stdcbench will run and report its results via USART1. You can see them using a terminal program configured for 9600 baud, no parity, 8 bits, 1 stop bit and no flow control. They should look like this (the benchmark numbers may vary depending on the SDCC version used to compile stdcbench):

stdcbench 0.6
stdcbench c90base score: 118
stdcbench c90lib score: 91
stdcbench final score: 209


Download a version of Whetstone adapted for use with the STM8/128-EVAL board, and proceed by unpavking invoking make. sdcc 3.8.0 does not support double. It replaces double by float and emits a warning to the user. Thus the scores from Whetstone obtained using sdcc 3.8.0 are not really comparable to those from other platforms (but as of late 2018, all other compilers targeting the STM8 do the same, so they are at least comparable to other scores for the STM8). Unlike stdcbench, Whetstone runs the full benchmark before doing any text output, so don't worry when it takes some time until something appears on the terminal.

Loops: 10, Iterations: 1, Duration: 8827 msec.
C Converted Double Precision Whetstones: <NO FLOAT> KIPS

Since printf() from sdcc 3.8.0 does not have float support by default, you have to calculate the KIPS score from the data in the first row by hand: Multiply Loops by 100, divide by the duration in seconds. In this case we get a score of 113.2887 KIPS.

More about stm8flash

stm8flash was written by Valentin Dudouyt. It works both with stlink (including the one integrated on the discovery boards) and stlinkv2 devices. The programmer can be selected using -c stlink or -c stlinkv2. The target device is selected using the -p option (to get a list of target devices, use the -p option with an option argument that is not an stm8 device, e.g. -p help. stm8flash will treat filenames ending in .ihx or .hex as Intel hex, and other filenames as binaries.

More about SDCC

SDCC was initially written by Sandeep Dutta for the MCS-51, and has a relatively conservative architecture (see Sandeep Dutta, "Anatomy of a Compiler", 2000). It has been extended by various contributors and more recently, incorporated some cutting-edge technologies, in particular in register allocation (see Philipp Klaus Krause, "Optimal Register Allocation in Polynomial Time", 2013). The stm8 backend was mostly written by Philipp Klaus Krause for his research into bytewise register allocation and spilling (see Philipp Klaus Krause, "Bytewise Register Allocation", 2015).

SDCC is a C compiler that aims to be compliant with the C standards.

Important compiler options for STM8 developers include: