Implement support for HSPI overlap mode

[pablo-mendoza]

Hey this implement Issue #1062. Allows activation of HSPI overlap mode. I tested this with a 23LC1024 memory and it worked fine. But couldn't make it work with an SD card. The SD card was getting confused by the sharing of the SPI bus.

[codecov-io]

Codecov Report

Merging #3189 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #3189   +/-   ##
======================================
  Coverage    27.6%   27.6%           
======================================
  Files          20      20           
  Lines        3655    3655           
  Branches      678     678           
======================================
  Hits         1009    1009           
  Misses       2468    2468           
  Partials      178     178

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ca3a172...cdfd347. Read the comment docs.

[igrr]

The file used to be formatted with 4 spaces, could you please adjust indentation in your changes?

[igrr]

I would rather suggest keeping just miso/miso/sck/ss arguments. You can determine _pinSet value internally.

Another point, do Arduino libraries typically call SPI.begin internally? If so, maybe adding an independent .pins method would be a more portable choice. That way, one could first call SPI.pins in the sketch and then call .begin method of another library which would do SPI.begin internally.

[igrr]

If going with begin method, suggest at least making it take the same arguments as it does in the ESP32 library:
https://github.com/espressif/arduino-esp32/blob/master/libraries/SPI/src/SPI.h

[pablo-mendoza]

I think I submitted the updated changes (I suck at git).

I like your idea of adding an interface to setup the SPI before the call to SPI.being, as you say most libraries just call it internally.

I'm kind of wary of this SPI::pins interface as, in absence of SoftwareSPI there's just two magical set of pins that work. And even if we implement SoftSPI all three modes are different enough that I'd rather the caller set explicitly where they want normal HSPI, overlapped HSPI or SoftwareSPI.

There are a lot of caveats in overlap mode that I'm in doubt that any library designed for Arduino(avr) is going to work out of the box. First and foremost you can't use any random GPIO for the SS line in overlap mode, you MUST use GPI0 as Hardware CS, otherwise you would likely be asserting your GPIO CC when the flash is using the pins.

Now since you are using hardware CS it will deassert your device after every write/transfer. Since most arduino libraries are only doing single byte read/transfers the devices will be constantly asserted/deasserted, but at least the 23LC1024 I used to test this expects CS to be LOW for the entire transfer of a whole address/write so you need to convert existing libraries to use SPI.writeBytes/SPI.transferBytes otherwise they will not work.

Let me know what you think.

[pablo-mendoza]

Also I didn't updated the documentation my in latest changes. I would do that once we agree on an interface.

[igrr]

Okay, this version with pins method looks good to me. Please re-indent again, some lines still have tabs.

[pablo-mendoza]

Done, I removed the tabs, updated the doc and squashed all the commits back into one.