Trouble using Seeed XIAO ESP32-C3 with 7.5" BW display

[xiugaze]

Hi,
I have a thread open on the Arduino forum discussing this issue here, but I was pointed to this discussion page for additional help.

I have a basic sketch using this display working on an Espressif S3 development board. Here is the stripped down bare-minimum working sketch:

#define MAX_DISPLAY_BUFFER_SIZE 65536ul
#define MAX_HEIGHT(EPD) (EPD::HEIGHT <= MAX_DISPLAY_BUFFER_SIZE / (EPD::WIDTH / 8) ? EPD::HEIGHT : MAX_DISPLAY_BUFFER_SIZE / (EPD::WIDTH / 8))
GxEPD2_BW<GxEPD2_750_T7, MAX_HEIGHT(GxEPD2_750_T7)> display(GxEPD2_750_T7(GxEPD2_750_T7(15, 1, 26, 4)));
SPIClass hspi(HSPI);

void fill_black() {
  display.setFullWindow();
  display.firstPage();
  do
  {
    display.fillScreen(GxEPD_BLACK);
  }
  while (display.nextPage());

}

void display_init() {
  hspi.begin(13, 12, 14, 15); 
  display.epd2.selectSPI(hspi, SPISettings(4000000, MSBFIRST, SPI_MODE0));
  display.init(115200);
  display.setRotation(1); // portrait
  Serial.println("display initialized");
}
void setup() {
  Serial.begin(9600);
  while(!Serial) {};
  delay(3000);
  display_init();
  fill_black();
}

I know that there are some issues with this sketch. First, I understand that the usage of SPIClass::begin() that I took from the ESP32 Driver example sketch was in place to compensate for a weird pin assignment on the Waveshare ESP32 driver board. I understand that the idiomatic way to do this is to simply call display.init(), which will use the SPI pins defined in Pins_Arduino.h. However, this sketch works to fill the screen as intended anyway.

However, I am attempting to get this same sketch running on a Seeed XIAO ESP32-C3 development board. I've tried multiple permutations of the same sketch using different display initialization code without success.

I have been told on the Arduino forum that just calling GxEPD2_BW::init(115200) is the idiomatic way to set up the display and SPI bus. From reading through the source for SPIClass::begin, I think that this uses the SPI pins defined in Pins_Arduino.h, which, for this board, are

static const uint8_t SS    = 20;
static const uint8_t MOSI  = 10;
static const uint8_t MISO  = 9;
static const uint8_t SCK   = 8;

However, using the following initialization code doesn't work.

void display_init() 
  display.init(115200);
  display.setRotation(1); // portrait
  Serial.println("display initialized");
}

I have also tried inserting the following before display.init() in my display_init() function without success:

hspi.begin(13, 12, 14, 15); // shot in the dark

// following four should all do the same exact thing. 
hspi.begin(SCK, MISO, MOSI, SS); 
hspi.begin();
hspi.begin(-1, -1, -1, -1);
hspi.begin(D8, D9, D10, D7); 

I know that the display is not damaged because I have switched back to the S3 development board which works fine. As additional context, #74 suggests that at least one person has tried to get a Waveshare display connected to a XIAO C3 board over SPI successfully, seemingly using the exact same pins that I am trying to use.

Thanks in advance, any help is appreciated.

[xiugaze]

To clarify further, here is the pin mapping I am using between the board and the Waveshare driver HAT:

D20 (SS/CS) -> CS
D10 (MOSI) -> DIN
D8 (SCK/CLK) -> CLK
D4 -> DC
D5 -> RST
D6 -> BUSY

and the display constructor looks like:

GxEPD2_BW<GxEPD2_750_T7, MAX_HEIGHT(GxEPD2_750_T7)> display(GxEPD2_750_T7(/* CS */ SS, /* DC */ D4, /* RST */ D5, /* BUSY */ D6));

[G6EJD]

Also don't use Dnumber nomenclature use the actual GPIO numbers so just 10 or 8 etc.
I notice in your examples the PIN numbers didn't match what's available on the board.

[xiugaze]

From https://wiki.seeedstudio.com/XIAO_ESP32C3_Getting_Started/#hardware-overview:

From pins_arduino.h:

static const uint8_t SS    = 20;
static const uint8_t MOSI  = 10;
static const uint8_t MISO  = 9;
static const uint8_t SCK   = 8;
/* ... */
static const uint8_t D0 = 2;
static const uint8_t D1 = 3;
static const uint8_t D2 = 4;
static const uint8_t D3 = 5;
static const uint8_t D4 = 6;
static const uint8_t D5 = 7;
static const uint8_t D6 = 21;
static const uint8_t D7 = 20;
static const uint8_t D8 = 8;
static const uint8_t D9 = 9;
static const uint8_t D10 = 10;

D<number> is defined for the digital pins, and identifiers are defined for the SPI pins.

[G6EJD]

display(GxEPD2_750_T7(/* CS */ SS,

Not CS as you've defined? So it uses the predefined SS

[xiugaze]

Not sure what you mean by "CS as you've defined", but SS resolves to the pin definition in pins_arduino.h, which is SS = 20.

[G6EJD]

You said:
D20 (SS/CS) -> CS
D10 (MOSI) -> DIN
D8 (SCK/CLK) -> CLK
D4 -> DC
D5 -> RST
D6 -> BUSY

And were using:
GxEPD2_BW<GxEPD2_750_T7, MAX_HEIGHT(GxEPD2_750_T7)> display(GxEPD2_750_T7(/* CS / SS, / DC / D4, / RST / D5, / BUSY */ D6));

[G6EJD]

You have to define the spi bus using what you've defined:

static const uint8_t SS = 20;
static const uint8_t MOSI = 10;
static const uint8_t MISO = 9;
static const uint8_t SCK = 8;

And of course make sure the display is connected to those pins. I've used the C3 variant without any issues.

[xiugaze]

I'm not defining those pin identifiers, those are defined and included in Pins_Arduino.h. I'm not sure what you mean by "define the SPI bus". Do I need to call SPIClass::begin using those pin identifiers? Regardless, I've tried both ways with no success. If you could show code that you've gotten working with this board, that would be great. Here's the source for SPIClass::begin, which seems to default to the pin definitions for SS, MOSI, MISO, and SCK defined in Pins_Arduino.h when no arguments are passed:

void SPIClass::begin(int8_t sck, int8_t miso, int8_t mosi, int8_t ss)
{
    if(_spi) {
        return;
    }

    if(!_div) {
        _div = spiFrequencyToClockDiv(_freq);
    }

    _spi = spiStartBus(_spi_num, _div, SPI_MODE0, SPI_MSBFIRST);
    if(!_spi) {
        return;
    }

    if(sck == -1 && miso == -1 && mosi == -1 && ss == -1) {
#if CONFIG_IDF_TARGET_ESP32S2 || CONFIG_IDF_TARGET_ESP32S3
        _sck = (_spi_num == FSPI) ? SCK : -1;
        _miso = (_spi_num == FSPI) ? MISO : -1;
        _mosi = (_spi_num == FSPI) ? MOSI : -1;
        _ss = (_spi_num == FSPI) ? SS : -1;
#elif CONFIG_IDF_TARGET_ESP32C3
        _sck = SCK;
        _miso = MISO;
        _mosi = MOSI;
        _ss = SS;
#else
        _sck = (_spi_num == VSPI) ? SCK : 14;
        _miso = (_spi_num == VSPI) ? MISO : 12;
        _mosi = (_spi_num == VSPI) ? MOSI : 13;
        _ss = (_spi_num == VSPI) ? SS : 15;
#endif
    } else {
        _sck = sck;
        _miso = miso;
        _mosi = mosi;
        _ss = ss;
    }

    spiAttachSCK(_spi, _sck);
    spiAttachMISO(_spi, _miso);
    spiAttachMOSI(_spi, _mosi);

}

[G6EJD]

Yes you need to define the spi bus pins regardless of what the IDE is doing, so spi.begin(SCK, MISO, MOSI, SS);

static const uint8_t SS = 20;
static const uint8_t MOSI = 10;
static const uint8_t MISO = 9;
static const uint8_t SCK = 8;

I'm using the 7.5" B/W display.

I'm working away just now, so don't have access to the source code.

My experience is your display type is not what you think and therefore are selecting the wrong display object, or there's a wiring fault.

[xiugaze]

Thank you for your quick responses and for your attempts to help. Unfortunately I don't think you are correct as far as manually calling spi.begin().

• A call to GxEPD2_BW::init() actually calls GxEPD2_EPD::init() in GxEPD2_EPD.cpp
• GxEPDG2_EPD::init() calls _pSPIx->begin() (notably with no arguments).
• _pSPIx->begin() (in SPI.cpp which includes Arduino.h which includes pins_arduino.h, which defines SCK, MISO, MOSI, and SS as above) with no arguments does (for C3 boards):

_sck = SCK;
_miso = MISO;
_mosi = MOSI;
_ss = SS;

/* ... */

spiAttachSCK(_spi, _sck);
spiAttachMISO(_spi, _miso);
spiAttachMOSI(_spi, _mosi);

So in short, display.init() should just initialize SPI properly with the same pins that I am using.
Additionally, while you might be right that I'm using the wrong constructor for this display, I would hedge a bet that either I am not using the wrong one, or it doesn't matter, since the sketch I showed above works properly on an S3-based development board.

[xiugaze]

Quick update on this: I got some XIAO-S3 boards in today and tried with the same sketch, same pins. Worked like a charm. I am wondering if I just have a bad C3 board. Here's the full working sketch for reference.

#define MAX_DISPLAY_BUFFER_SIZE 65536ul
#define MAX_HEIGHT(EPD) (EPD::HEIGHT <= MAX_DISPLAY_BUFFER_SIZE / (EPD::WIDTH / 8) ? EPD::HEIGHT : MAX_DISPLAY_BUFFER_SIZE / (EPD::WIDTH / 8))
GxEPD2_BW<GxEPD2_750_T7, MAX_HEIGHT(GxEPD2_750_T7)> display(GxEPD2_750_T7(/* CS */ D7, /* DC */ D4, /* RST */ D5, /* BUSY */ D6));

void setup() {
  Serial.begin(9600);
  while(!Serial) {};
  delay(3000);

  display_init();
  fill_black();
}

void loop() { }

void display_init() {
  display.init(115200);
  display.setRotation(1); // portrait
  Serial.println("display initialized");
}

void fill_black() {
  display.setFullWindow();
  display.firstPage();
  do
  {
    display.fillScreen(GxEPD_BLACK);
  }
  while (display.nextPage());
}

[ZinggJM]

Do both processors use the same strapping pins?

[ZinggJM]

I would need to know what connection module you use.
Is it the Waveshare HAT with level converters? You may need to add 10k resistors to the strapping pins.

I suggest you try with GxEPD2_Example or GxEPD2_HelloWorld. Report diagnostic output from Serial Monitor.

I don't have these XIAOs, but I think I have a C3. So as last resort I could also try. Maybe later.

[G6EJD]

I'm back at home now: My setup for the XIAO ESP32C3 and GxEPD2
// Connections for XIAO ESP32C3
static const uint8_t EPD_BUSY = D5;
static const uint8_t EPD_CS = D1;
static const uint8_t EPD_RST = D0;
static const uint8_t EPD_DC = D3;
static const uint8_t EPD_SCK = D8;
static const uint8_t EPD_MISO = -1; // Master-In Slave-Out not used, as no data from display
static const uint8_t EPD_MOSI = D10;

GxEPD2_BW<GxEPD2_426_GDEQ0426T82, GxEPD2_426_GDEQ0426T82::HEIGHT> display(GxEPD2_426_GDEQ0426T82(/CS=D8/ EPD_CS, /DC=D3/ EPD_DC, /RST=D4/ EPD_RST, /BUSY=D2/ EPD_BUSY)); // GDEQ0426T82 480x800, SSD1677 (P426010-MF1-A)

And:
SPI.begin(EPD_SCK, EPD_MISO, EPD_MOSI, EPD_CS); // re-configure SPI bus

[ZinggJM]

Hi @G6EJD , thank you for your contribution!

And for showing how to re-map SPI pins of the global SPI instance, before calling display.init(...).
Explanation: display.init() will also call SPI.begin(), but this call does nothing if it has been called before, and no SPI.end() is called in-between.

I would be interested in learning your reason to use different SPI pins than the default.
(because of the adapter board, I assume).

[G6EJD]

I wasn't using the default I2C bus so chose D5 for CS, but could have used D2, but I'm using the DS18B20 a one-wire interface. All other pins are default for the SPI bus. I could have used the default SPI pins defined in the IDE but always define them myself so I can use the same nomenclature across programme versions.

I've used nearly all display types in existence (at least supported by your library) with the XIAO interface board with no issues.

[G6EJD]

This is what I sue for the XIAO boards, saves a lot of effort:

https://thepihut.com/products/epaper-breakout-board

[ZinggJM]

Thank you for the link!

But this board doesn't have a switch or other means to adapt the RESE resistor of the booster circuit.
The value should be 0.47 ohms for UltraChip controllers, 2ohms or 3ohms for SSD controllers.

I just got an e-mail from Seeed; they also have an adapter board, matching for XIAOs. I didn't look at it yet.