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eclipse / mraa

Linux Library for low speed IO Communication in C with bindings for C++, Python, Node.js & Java. Supports generic io platforms, as well as Intel Edison, Intel Joule, Raspberry Pi and many more.
http://mraa.io
MIT License
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How to initialize RTS/CTS pins on Edison? #588

Open htot opened 7 years ago

htot commented 7 years ago

On Edison (miniboard / ardiono board) when initializing the uart the RX/TX pins are mapped and configured. However, when setting HW flow control (RTS/CTS) the pins are not configured.

Can that be done using mraa? Or should I duplicate code from src/x86/intel_edison_fab_c.c mraa_intel_edison_uart_init_pre and modify that init RTS/CTS?

alext-mkrs commented 7 years ago

You can use mraa_uart_set_flowcontrol() function for that, or a respective wrapper if you're using mraa from something else than C.

htot commented 7 years ago

Yeah, that will initialize the UART to use flow control. It will not enable the pin AFAIK, those are multiplexed with GPIO on Edison, the same way as RX/TX. The mode is changed in src/x86/intel_edison_fab_c.c mraa_intel_edison_uart_init_pre with the following lines:

ret = mraa_intel_edison_pinmode_change(130, 1); // IO0 RX
ret = mraa_intel_edison_pinmode_change(131, 1); // IO1 TX

Unfortunately mraa_intel_edison_pinmode_change is a static function.

arfoll commented 7 years ago

So this commit will hopefully give you a temp fix https://github.com/intel-iot-devkit/mraa/commit/563bf708c636d6068e989d78e1d67e88fd8ae947. However this is quite a complex issue so will need substantial testing before I add something like this in.

htot commented 7 years ago

Yes, something like this did occur to me. But I think my application will break later when something definite goes in. Thus my suggestion to copy/paste something similar into my application.

The real question is how initializing rtx/cts should fit into mraa best. Currently afaik on edison the pins are never initialized. Your patch will always initialize them (so disable gpio on these pins).

Currently mraa_uart_init does not take an option that would allow conditionally initializing rts/cts. And adding that would break all existing application code. It could be added to mraa_uart_set_flowcontrol(), but that would be a late point to configure pins and probably that function should not depend on hardware/platform.

So what could be a definite solution then? Create a function mraa_pin_option() that should be called before mraa_uart_init? Such a function could be made to have zero effect on other platforms and when not called mraa_uart_init could default to the current not changing the rts/cts pin mode.

alext-mkrs commented 7 years ago

In general, there's an infrastructure of so called advanced functions, essentially platform-specific ones, which override (_replace) or run before (_pre) or after (_post) the generic one. So mraa_uart_set_flowcontrol() could theoretically be overridden for Edison in a way that setting the rts/cts to true would trigger pin reconfiguration. Not sure though if that's possible at arbitrary point in time, haven't looked at what specifically that reconfiguration would entail.