SPI won't work

HiFive1 Rev B
1

Hello everyone. I’m trying to communicate to a FLASH Memory (W25Q64) via SPI, but it won’t work. I’ve tried with multiple modules.
I’m sending a message of four bytes (90h;00;00;00) to which the module should answer with its manufacturer/device ID in 2 bytes.
This is the code I’m using. I’m not able to check with an oscilloscope given that I haven’t got one.

int main (void)
{

    set_freq_320MHz();

    uint16_t sckdiv;
    sckdiv = cpu_freq / (2 * 80000) - 1;

    GPIO_REG(GPIO_IOF_EN) |= (1 << GPIO_SPI1_MISO);
    GPIO_REG(GPIO_IOF_SEL) &= ~(1 << GPIO_SPI1_MISO);

    GPIO_REG(GPIO_IOF_EN) |= (1 << GPIO_SPI1_MOSI);
    GPIO_REG(GPIO_IOF_SEL) &= ~(1 << GPIO_SPI1_MOSI);

    GPIO_REG(GPIO_IOF_EN) |= (1 << GPIO_SPI1_SCK);
    GPIO_REG(GPIO_IOF_SEL) &= ~(1 << GPIO_SPI1_SCK);

    GPIO_REG(GPIO_IOF_EN) |= (1 << GPIO_SPI1_SS0);
    GPIO_REG(GPIO_IOF_SEL) &= ~(1 << GPIO_SPI1_SS0);

    GPIO_REG(GPIO_IOF_EN) |= (1 << 2);
    GPIO_REG(GPIO_IOF_SEL) &= ~(1 << 2);
    SPI1_REG(SPI_REG_CSDEF) = 0xFFFFFFFFUL;

    SPI1_REG(SPI_REG_CSID) = 0;
    SPI1_REG(SPI_REG_CSMODE) = SPI_CSMODE_HOLD;

    uint8_t instr[8] = {0x90, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
    uint8_t recv[2];

    SPI1_REG(SPI_REG_CSDEF) &= ~(1 << 0);

    for(int i = 0; i < 4; i++) {
    	while (SPI1_REG(SPI_REG_TXFIFO) & SPI_TXFIFO_FULL)
    	{
    		asm volatile("nop");
    	}
    	SPI1_REG(SPI_REG_TXFIFO) = instr[i];

        while (SPI1_REG(SPI_REG_RXFIFO) <= 0xFF)
            ;
    }

    unsigned long data;

    for(int i = 0; i < 2; i++) {
    	while (1) {
            data = SPI1_REG(SPI_REG_RXFIFO);  // Read the RX register EXACTLY once
                if (data <= 0xFF) {  
                    break;
                }
            }
    	recv[i] = (char) (data & 0xFF);
    }


    SPI1_REG(SPI_REG_CSDEF) |= (1 << 0);

    while (1)
    {
    }

    return 0;
}

EDIT:
The amount of data received before the RXFIFO becomes empty is exactly of the amount requested.
E.g. Request Manufacturer/Device ID, 2 bytes (0x00) received
Power Up Device, 0 bytes received, as per datasheet
But this happens only if I detach the CS from hardware control and pull high/low the relevant GPIO pin. If it is in HW control, using HOLD, it receives nothing.

2

Is it possible that this accidentally consumes the result as well? Might want to adapt it to only read one byte at most.

3

I already tried that. I just keep receiving zeros

EDIT:
The amount of data received before the RXFIFO becomes empty is exactly of the amount requested.
E.g. Request Manufacturer/Device ID, 2 bytes (0x00) received
Power Up Device, 0 bytes received, as per datasheet