Expose setting to select SPI bus for ESP32

[sidoh]

ESP32s have multiple SPI busses.

With GxEPD2, the user is supposed to configure the global SPI instance, which it then uses.

To change the SPI bus, one must do the following:

SPI.end();
SPI.begin(13, 12, 14, 15); // replace these with the appropriate SPI pins

[Ivanverdonck]

Hi,

Where does this code need to be added?
I have a Waveshare ESP32 driver board. I tried adding this to the setup(), but this did not work.

I use a waveshare - GDEW075Z09 7.5" b/w/r
Is it possible to use the red color?

Kind regards,
Ivan

[sidoh]

Hi Ivan,

If you're making the modification yourself, it should be enough to drop it somewhere in main.cpp (initDisplay is probably a good place https://github.com/sidoh/epaper_templates/blob/master/src/main.cpp#L54).

You might need to adjust the other pins as well (dc, rst, busy).

Unfortunately not currently possible to use the multi-color displays.

[nullstalgia]

Notes:

SPI.end();
SPI.begin(13, 12, 14, 15); // replace these with the appropriate SPI pins

Can go both above and below the current initDisplay() code. Example from the E-Paper driver lib.

I personally do it above, but that's just me.

---

Also, this library requires the default hardware SPI bus pins. My tests with changing those SPI pins ends up with the display doing nothing.

There is an internal fork for using Software SPI, but the author does not recommend that.

Luckily, the ESP32 has a spare bus (as shown by @sidoh above) that works fine when using it's set of pins.

SPI1 isn't usually allowed to be used by users, as it's commonly used for SPI RAM (PSRAM), and SPI0 is the main system flash.

(If you wish, you can set up the PSRAM bus, but I would not recommend it)

As such, I put forth this suggestion for selecting the 2 free busses. This would fit best on the Hardware tab in the Settings page.

[nullstalgia]

I started a little bit yesterday, but I got chumped when it came to the Web interface once again 😅

The main bit that matters is this:

...
void initDisplay() {
  #if defined(ESP32)
    if(settings.hardware.spi_bus != HSPI){
        if (settings.hardware.spi_bus == VSPI){
            SPI.end();
            SPI.begin(18, 23, 19, 5);
        }
    }
  #endif
  if (display) {
    delete display;
    display = NULL;
  }
...

And in case you're not using an editor that shows the definitions of HSPI/VSPI easily, here are screenshots from VSCode

[nullstalgia]

@sidoh, we should be good to close this if you feel the new features are satisfactory. :)