[Epic] - Gain deep understanding of mbed os

[ladislas]

It's important do precisely study and understand how mbed works, the different API, drivers & communication stacks.

This issue of type: epic will be used to gather information, share what we have learned and things that could be useful in the future.

Resources

• Github repo: https://github.com/ARMmbed/mbed-os/
• Mbed OS Documentation: https://os.mbed.com/docs/mbed-os/v5.14/introduction/index.html
• Mbed Reference Book: https://os.mbed.com/docs/mbed-os/v5.14/reference/index.html
• Mbed Doxy Documentation: https://os.mbed.com/docs/mbed-os/v5.14/mbed-os-api-doxy/modules.html
• Mbed APIs: https://os.mbed.com/docs/mbed-os/v5.14/apis/index.html
• Mbed Tutorials: https://os.mbed.com/docs/mbed-os/v5.14/tutorials/index.html
• Mbed Tools/Testing: https://os.mbed.com/docs/mbed-os/v5.14/tools/testing.html

[ladislas]

Communication / Command Processing

In our avr prototype, we use a homemade circular buffer to group commands before processing.

• https://github.com/leka/LKAlphaOS-avr/blob/develop/lib/Buffer/Buffer.h
• https://github.com/leka/LKAlphaOS-avr/blob/develop/lib/Buffer/Buffer.cpp

mbed provides something similar with built-in critical sections lock so it can be used from ISR (if needed).

https://os.mbed.com/docs/mbed-os/v5.14/apis/circularbuffer.html

Both have push/write, pop/read, peek/peek and status functions.

Our buffer also has a hasPattern function to look for specific patterns inside the buffer, e.g. the start sequence (https://github.com/leka/LKAlphaComSpecs/#start-sequence)

https://github.com/leka/LKAlphaOS-avr/blob/develop/lib/Buffer/Buffer.cpp#L153

[ladislas]

Thread synchronization with EventFlags

https://os.mbed.com/docs/mbed-os/v5.14/apis/eventflags.html

I haven't tested it, but EventFlags could be a very nice tool to synchronize our threads with the wait_any function:

https://os.mbed.com/docs/mbed-os/v5.14/mbed-os-api-doxy/classrtos_1_1_event_flags.html#a666b81f3ea18439300f8c6d88cacad80

For LED animation, something like this could work, we need to try it out:

// inside a thread function doing the animation
while(true) {
	// ...
	leds.shine(200, 34, 78);
	if event_flags.wait_any(STOP_FLAG, 10/*ms to wait*/) != 0 {
		break; // break from while loop
	}
	leds.shine(150, 34, 90);
	// ...
}

The same tool can be used to "start" threads.

signal_wait should also be explored:

https://os.mbed.com/docs/mbed-os/v5.14/mbed-os-api-doxy/classrtos_1_1_thread.html#a2b0659360b5cb4b1273d2362398c0294

[ladislas]

Simplify your code with mbed-events

• https://os.mbed.com/blog/entry/Simplify-your-code-with-mbed-events/