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AFSK (Audio frequency shift keying) was used primarily for slow – 1200baud – packet radio. Today it is mainly used by HAMs for APRS(tm).
The most common setup is to have radio equipment with TNC (terminal node controller) connected to host PC. Host is running some software that understands incoming packets and reacts to them. If you are a HAM you probably have radio and PC already. What you need is the TNC. General problem I found with TNCs is that they tend to cost too much – 100+EUR price tag is not uncommon for 5-10year old equipment, and new TNC models cost 200+EUR (lots of features not necessary for AFSK operation).
You have probably noticed there is more power in the STM32 processors than simple tasks can use. In this case you probably want to run some more “tasks”.
FreeRTOS has just the stuff you need – tasks, mutexes/semaphores, queues.
Unfortunately I ran into trouble with newlib and FreeRTOS not playing nicely as they should. Memory allocation (malloc) didn’t work as expected and caused the CPU to Bus-Fault. Then I realized there is another allocator in the FreeRTOS, and why does one need 2 allocators on embeded system ?