fast pin access

[m-mcgowan]

This covers fast pin set/reset. Does anyone have a suggestion for multiple pin set/reset, port access etc..?

[satishgn]

Yes. Bit-banding is available on ARM Cortex-M3 which is the fastest/atomic way to set/reset IO pins.
Please feel free to assign it to me. I can take this up in my spare time after hardware design.
For more info on this: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0337h/Behcjiic.html

[m-mcgowan]

Good call satish - right now focus is primarily on the API (as you see the implementation is simple), when that API settles down feel free to add a bit-banding implementation if you wish. I'm curious exactly how much faster bit banding will be and how fast do we need it to be?

[ScruffR]

May be a bit late, but for consistency with digitalWriteFast() would not pinSetFast()/pinResetFast() be "nicer" ;-)

About bit-banding, I had used this macro in an RGBMatrixPanel lib together with Paul
#define portSetMasked(_port, _word, _mask) (_port->BSRR = (_mask << 16) | (_word & _mask))

It`s not quite bit-banding, but it's atomic and somewhat fast too.

http://community.particle.io/t/some-reusable-macros-and-stuff/8846

I did some timing tests on the interrupt routine that does other things too, but the port write was notably faster.

http://community.particle.io/t/adafruit-16x32-rgb-led-matrix/5119/107

[technobly]

Yep, Mat made them all consistent with Fast at the end.

I'm pretty excited about this bit-banding thing... have not experimented with that but it sounds super powerful for fast access.

[pkourany]

Oh, I like the bit banding. Nice catch @satishgn. @ScruffR, the whole port write IS fast and doing it with bit banding would not be faster IMO. But for single bit operations, to the user, it would be transparent via @m-mcgowan 's API but under the hood it would be as fast as it gets. @satishgn, I would love to see your propose implementation.

[m-mcgowan]

We can expand with port writes as another PR. Is everyone happy with this as it is so it can be included for the imminent 0.4.2 release?

[pkourany]

I agree, do as another PR

[technobly]

Has anyone really tested this? Personally I have not had the time but really want to before we release it.

[ScruffR]

@technobly, tested what? Bit-banding or my portSetMasked()?
The latter is tested on the Core and the books tell that this should work on the Photon just the same, but I haven't tested it - due to lack if HW ;-)

@m-mcgowan, I'm fine with that 👍

[technobly]

Tested the speed of inline functions setting and clearing GPIO, vs macros we are currently using. Anyone have a scope besides me?

[pkourany]

@technobly, I have a scope and logic analyzer but I can only test late tonight or tomorrow. What did you test on (Core vs Photon) and what were the timings? Can you post your test code so I can duplicate?

[technobly]

Easiest thing to do is look at v006 of the NeoPixel library with a scope. First verify my documented timings with a scope for WS2812B with Photon and Core, not logic analyzer. Then swap out the macros for these new inline functions. Appreciate the help Paul!

[m-mcgowan]

Hi Everone, I'm preparing a 0.4.2 release, so going to merge this in. If any bugfixes are needed, we can discuss those as separate issues.