STM32 TFT not displaying solid color

Question

I am trying to use this display with an STM32F0 using SPI. I begin by setting up the peripherals using the following

RCC->AHBENR |= RCC_AHBENR_GPIOBEN;
RCC->APB1ENR |= RCC_APB1ENR_SPI2EN;

GPIOB->MODER |= (0x2 << (2*12)) + (0x2 << (2*13)) + (0x2 << (2*15)) +
                (0x1 << (2*11)) + (0x1 << (2*10));

SPI2->CR1 |= SPI_CR1_BIDIMODE + SPI_CR1_BIDIOE + SPI_CR1_MSTR + SPI_CR1_BR;
SPI2->CR2 |= SPI_CR2_SSOE + SPI_CR2_NSSP;
SPI2->CR1 |= SPI_CR1_SPE;

In other words, I enable the clock to the peripherals, enable alternate funtions for the SPI NSS, MOSI, and SCK pins, as well as for the manually controlled D/CX and RST pins. I enable bidirectional mode and enable the SPI. I then initialize the LCD using commands adapted from Crystalfontz' Arduino example code (which I will not post to save space). However, once the initialization is done, the screen displays the following.

Clearly, this is not what I want. I attempt to fill the screen using the following functions.

void SPI_sendCommand(uint8_t command) {
    CLR_RS;
    while (!(SPI2->SR & SPI_SR_TXE));
    SPI2->DR = command;
    while (!(SPI2->SR & SPI_SR_TXE));
}

void SPI_sendData(uint8_t data) {
    SET_RS;
    while (!(SPI2->SR & SPI_SR_TXE));
    SPI2->DR = data;
    while (!(SPI2->SR & SPI_SR_TXE));
}
void setDisplayWindow(int x0, int y0, int x1, int y1) {
    SPI_sendCommand(ST7789_CASET);   // Column Address Set
    SPI_sendData(x0>>8); // X address start:
    SPI_sendData(x0);        // 0 <= XS <= X
    SPI_sendData(x1>>8); // X address end:
    SPI_sendData(x1);        // S <= XE <= X

    SPI_sendCommand(ST7789_RASET); //Row address set
    SPI_sendData(y0>>8); // Y address start:
    SPI_sendData(y0);        // 0 <= YS <= Y
    SPI_sendData(y1>>8); // Y address start:
    SPI_sendData(y1);        // S <= YE <= Y

    SPI_sendCommand(ST7789_RAMWR); //write data
}
void fillLCD(uint8_t R, uint8_t G, uint8_t B) {
    setDisplayWindow(0, 0, 239, 239);
    SET_RS;
    for (h = 0; h < 240; h++) {
        for (w = 0; w < 240; w++) {
            while (!(SPI2->SR & SPI_SR_TXE));
            SPI2->DR = R;
            while (!(SPI2->SR & SPI_SR_TXE));
            SPI2->DR = G;
            while (!(SPI2->SR & SPI_SR_TXE));
            SPI2->DR = B;
            while (!(SPI2->SR & SPI_SR_TXE));
        }
      }
    CLR_RS;
}

where CLR_RS and SET_RS clear and set the D/CX pin, respectively. These functions do not do their job, but are almost identical to the ones in the example code. My pins are set up as follows.

1  - GND                2  - Vcc (3.3 V)
3  - Open               4  - Open
5  - GND                6  - Vcc
7  - Vcc                8  - GND
9  - PB13 (SCL)         10 - PB15 (MOSI)
11 - Open               12 - PB11 (D/CX)
13 - PB12 (NSS)         14 - GND
15 - PB10 (RST)         16 - GND
17 - Open               18 - GND

I believe the issue may be with how I write data bytes to the SPI, as commands that don't take parameters, like putting the display in sleep mode, work, while commands that take parameters, like changing the brightness, do not work. Does anyone have any idea how I can get just a solid color to display on this?

Answer 1

After getting this working on an MSP430 using nearly identical code, and staring hard at the oscilloscope, I realized that the SPI peripheral of the STM32 was performing 'data packing' on my bytes, resulting in 16 cycles per transfer rather than 8. I resolved the issue by using this method of setting SPI2->DR.

*((uint8_t *)&SPI2->DR) = (uint8_t)data;

Answer 2

first of all you disable the CS before the transmition is over. while (!(SPI2->SR & SPI_SR_TXE)); will not work. You need to wait for TC flag before disabling the CS.

This is one of the most common mistakes