Limitations
Compatibility with the Arduino world
I adopted the Arduino core functionality for the STM8S to set up a simple programming environment. But unfortunatly there is no free C++ compiler for these CPUs. This makes it impossible to do a full port of the whole enviroment and integrate it 100% in the Arduino world as it has been done for the STM32 and the ESP8266.
This is not a drop-in replacement for an AVR, but the programming API is still very, very similar. Adopting existing libraries from C++ to C for use with the simplified C API is often easy and can be done quite fast, depending on the degree of dependency on specific hardware features.
Using a converter/compiler like cfront to translate from C++ to C might be an option.
Float arithmetics
Floating point arithmetics is supported by the SDCC standard library, but it comes at a pretty high cost in terms of code space and CPU load. This is how much the generated code grows by using a single float operation compared to using a long int:
| Floating point operation | approx. code size |
|---|---|
| addition | 736 Bytes |
| subtraction | 754 Bytes |
| division | 673 Bytes |
| multiplication | 907 Bytes |
| sinf() or cosf() | 3346 Bytes |
| log10f() | 3437 Bytes |
The Arduino standard example '01. Basics/ReadAnalogVoltage' is a very simple simple program with only very little floating point arithmetics. But it already uses 7336 bytes of flash. A similar sketch using integer arithmetics results in much more compact code occuping only 3791 bytes.
Float does work, but is better to be avoided and replaced by fixed point arithmetics whenever possible.
Known problems using Windows
It works, but using the Arduino.mk makefile with Windows is slow. Very slow. Painfully slow. Compiling-the-Blink-example-takes-about-40-seconds kind of slow. Yes, seriously. No kidding. 40 seconds. Measured on a 3GHz machine with 4GB RAM.
There is no easy fix, the underlying problem is a fundamental one. It is not about the compilation itself, it is the way Makefiles are written and executed. The whole concept relies on forking subprocesses for all the shell calls. Unfortunately, there is nothing like a fork in Windows and to work around that is painfully slow.
It would be great if somebody would replace the painfully slow parameter checking part of the makefile (that causes the majority of forking) by a single shell script that gets called by the makefile and delivers the results in no time. Or use cmake. Or integrate it somehow into the STVD IDE (This STVD-SDCC integration suite might be useful). Or whatever.
Until then the least annoying way out might be using a virtual machine running a simple Linux system. Ubuntu Mate or a basic Debian install for example. Virtual Box is great for this purpose and freely available. The new Linux Subsystem feature of Windows 10 might be another option.